Med Sci Sports Exerc. 1995 Aug;27(8):1203-9.
Delecluse C, Van Coppenolle H, Willems E, Van Leemputte M, Diels R, Goris M.
The purpose of this study is to analyze the effect of high-resistance (HR) and high-velocity (HV) training on the different phases of 100-m sprint performance. Two training groups (HR and HV) were compared with two control groups (RUN and PAS). The HR (N = 22) and HV group (N = 21) trained 3 d.wk-1 for 9 wk: two strength training sessions (HR or HV) and one running session. There was a run control group (RUN, N = 12) that also participated in the running sessions (1 d.wk-1) and a passive control group (PAS, N = 11). Running speed over a 100-m sprint was recorded every 2 m. By means of a principal component analysis on all speed variables, three phases were distinguished: initial acceleration (0-10 m), building-up running speed to a maximum (10-36 m), and maintaining maximum speed in the second part of the run (36-100 m). HV training resulted in improved initial acceleration (P < 0.05 compared with RUN, PAS, and HR), a higher maximum speed (P < 0.05 compared with PAS), and a decreased speed endurance (P < 0.05 compared to RUN and PAS). The HV group improved significantly in total 100 m time (P < 0.05 compared with the RUN and PAS groups). The HR program resulted in an improved initial acceleration phase (P < 0.05 compared with PAS).
Saturday, August 2, 2008
Thursday, July 24, 2008
Effects of weighted vests and sled towing on sprint kinematics.
Sports Biomech. 2008 May;7(2):160-72.
Sprint running has been described as consisting of an acceleration phase, a maximum speed phase, and a deceleration phase. In sporting activities such as soccer, rugby, and football, sprint efforts are typically of short duration (e.g. 10–20m) (Spencer, Bishop, Dawson, and Goodman,2005). Therefore, the ability to develop maximal sprint speed in as short a time as possible (i.e. acceleration) may be of greatest significance in those sporting activities (Cronin and Hansen, 2006). Hay (1985) supported such a contention stating that, in many sporting activities, the success enjoyed by athletes is directly related to their ability to increase or decrease their speed rapidly.
An athlete’s ability to accelerate is dependent upon various factors, including technique (kinematics) and the force production capability (kinetics) of the body, in particular the lower limb musculature. Examples of kinematic factors that are considered important to sprint acceleration performance include step frequency and step length (Hunter, Marshall, and McNair, 2004), the duration of the stance phase, the position of foot strike relative to a vertical line through the athlete’s centre of mass, knee flexion angle at and immediately after footstrike, the magnitude of hip extension at toe-off, and the angle of take-off of the athlete’s centre of mass at toe-off. Examples of kinetic factors that are considered important to sprint acceleration performance include horizontal propulsive impulse of the ground reaction force.
Procedures
Sprint times for 10 and 30m were recorded for all runs filmed. Testing consisted of videoing (sagittal plane) athletes sprinting over a distance of 30m, from a standing start. Baseline film of an unresisted 30-m sprint was collected first to provide a baseline measure of sprint kinematics. Athletes were then filmed with two different loads (15% and 20% of body mass) wearing the vest, and with two different loads (15% and 20% of bodymass) towing a sled. Each athlete was therefore tested a total of five times (once for each condition) with 8-min rests between trials; the order of resisted conditions was randomized to avoid any test order bias. The load of 15% of body mass was chosen as it is commonly used for vest sprinting and sled towing, whereas the load of 20% was chosen to examine the effect of a heavier external load on sprint kinematics. Starting position for all sprints was standardized with athletes starting with the left foot forward. The left toe was placed 0.5m behind the starting line. The right toe was placed approximately level with the heel of the left foot.
Data analysis
The kinematics examined can be divided into two categories: step variables and joint angles. Step variables included step length (point of foot strike of one foot to the point of foot strike of the contralateral foot), step frequency (number of steps per second), stance phase duration (the time spent on the ground during each step), and swing phase duration (the time that the foot was not in contact with the ground). The joint kinematics examined included trunk, thigh, knee, and ankle joint angles at the beginning and at the end of the stance phase (i.e. footstrike and toe-off).
Results
Sprint times
The mean 10-m times ranged from 1.72s to 2.06s. Baseline 10-m times were significantly faster than in all the loaded conditions. Significantly slower 10-m sprint times were found for sled towing at 20% of body mass compared with both vest conditions, and for sled towing at 15% of body mass compared with vest sprinting at 15% of body mass. The differences in 10-m sprint times within the two vest conditions, within the two sled conditions, and between the sled (15% body mass) and vest (20% body mass) were found to be non-significant.
The 30-m times became slower as load increased in both the vest and sled conditions. The mean 30-m times ranged from 4.12s for the baseline sprint to 4.90s when towing a sled loaded at 20% of body mass. Baseline times were significantly faster than in all the loaded conditions. All other comparisons at 30m were found to differ significantly. That is, the heavier loads were slower within conditions and both sled loads were slower than both vest loads at 30m.
A significant training technique–distance effect was also found. The effect of resisted technique was different between 10 and 30m. Sled towing resulted in a greater overall sprint time (by 18.0–22.9%) at 10m compared with vest sprinting (by 7.5-10.0%). The effect of sled towing decreased (by 14.7–18.9%) as distance increased. However, the effect of the vests at both loads increased (by 9.3–11.7%) as distance increased.
Step variables
There was an increase in step length through the acceleration phase of sprinting. Significant technique and distance effects were found for step length. Step length differed significantly between baseline and all loaded conditions at all three distances (5, 15, and 25m). Step length during sled towing at 20% of body mass was significantly different from sled towing at 15% of body mass and both vest loads at all distances.
Significant differences were also observed with step frequency. Significant decreases (by 2.7–6.1%) in step frequency between the baseline sprint and all loaded conditions were found.
Stance phase and swing phase
Stance phase duration and swing phase duration showed a significant distance effect. Mean stance phase duration decreased as the athletes progressed over the 30-m distance. This was coupled with concurrent increases in swing phase duration. The stance phase duration was longer than the swing phase duration in the baseline condition at 5 and 15m but not at 25m. However, for all loaded conditions at all distances, swing phase duration did not exceed stance phase duration.
Stance phase duration and swing phase duration were found to differ significantly across technique. Stance phase duration in all loaded conditions was significantly greater than in the baseline condition at all distances from the start. The 20% of body mass loads with the sled and vest resulted in significantly longer stance phases compared with the sled at 15% of body mass at all distances from the start; however, there was no significant difference between the two vest loads. Swing phase duration was significantly shorter for all conditions compared with baseline values. However, there was a significant difference between the sled at 15% of body mass and vest and sled at 20% of body mass.
Joint kinematics
The trunk angles at foot strike during vest sprinting with 20% of body mass were significantly smaller (i.e. more upright) than those at baseline at all three distances from the start. Trunk angles at both foot strike and toe-off during sled towing with 15% and 20% of body mass were significantly greater than those at baseline and vest sprinting with 15% and 20% of body mass at all three distances from the start.
Discussion and Implications
Previous researchers have suggested that resisted sprinting techniques may have both acute and longitudinal effects on sprint technique. In the present study, we found that sled towing and vest sprinting influenced sprint kinematics during the acceleration phase of sprinting and that significant differences exist between the two resisted sprint-training techniques on some kinematic variables. As statistical analysis showed no athlete type effect, these findings can be applied to a variety of populations including athletes participating in team sports (such as rugby union) and both beach and track sprinting.
Sprint times and step variables
The effect of external load on sprint times was significant. Both sled towing and vest sprinting resulted in decreased sprint performance (i.e. increased sprint times of 7–23%) compared with unresisted sprinting in this study. To the authors’ knowledge, this is the first study to report the effect of vest loading on sprint times, whereas previous research has consistently reported decreased sprint performance during sled towing when compared with unresisted sprinting. However, the magnitudes of performance decrements differed across the studies (increases of 9-29%), which can be attributed to the differences in the load added, the sprint distance, the training levels of the athletes, and the design of the towing device used.
A greater effect on performance was observed when towing a sled compared with vest sprinting, when the same relative load was used. This finding is most likely related to the additional force required to overcome the effects of friction between the sled and the track surface. When the athlete attempts to move the sled, the ground exerts a horizontal force on the sled called the “force of static friction”. This frictional force acts in the opposite direction to the applied force; that is, it opposes the force that the athlete is applying. Once this force is overcome (by the athlete exerting a force greater than the force of static friction), the sled will begin to move. Therefore, in the initial stages of the sprint, the performance of the athlete was decreased significantly as he or she attempted to overcome the friction of the sled. Once the force of static friction was overcome, the effect of the towing load was decreased, as indicated by the 18% and 22.9% performance decreases for the 15% of body mass and 20% of body mass loads respectively at 10m, which were greater than the 14.7% and 18.9% decreases observed at 30m. A different pattern was observed during vest sprinting, with the performance decrease being greater at 30m than at 10m (7.5% and 10% decreases at 10m vs. 9.3% and 11.7% at 30m). These results suggest that the athletes had less additional force to overcome in the early stages of the sprint during vest sprinting; however, as they developed speed, the need to control the additional mass around their trunk resulted in decreased performance.
In this study, trunk angles during sled towing were significantly greater than at both baseline and in the vest condition at all distances from the start. This finding is consistent with previous research by Letzelter et al. (1995) and Lockie et al. (2003), who found similar trends of increasing trunk lean as the external load increased during sled towing. As suggested by Lockie et al. (2003) and Cronin and Hansen (2006), such a body position (i.e. large trunk lean) during sled towing seems to be specific to sprint acceleration movements. Therefore, sled towing may have the potential to overload the body in a manner specific to sprint acceleration and may be effective in improving sprint acceleration ability. In fact, a recent study by Zafeiridis et al. (2005) supports this hypothesis by showing that 8 weeks of sled towing improved sprint performance in the acceleration phase (0–20m) but not in the maximum speed phase (20–50m).
Greater trunk angles at foot strike during sled towing may decrease the braking forces associated with landing. A number of authors (Alexander,1989; Hunter et al., 2005; Mann and Herman,1985; Mann et al.,1982) have commented that to minimize the negative effect of horizontal and vertical braking on velocity, foot strike underneath and not in front of the athlete’s centre of mass is preferable during sprinting (i.e. the landing distance is smaller). During sled towing, an increase in trunk angle, without a concurrent increase in thigh flexion, allows foot strike to occur closer to the athlete’s centre of mass, possibly reducing braking and increasing the time for the production of propulsive forces. Similarly, if an athlete runs more upright without a concurrent decrease in thigh flexion at foot strike, foot strike will occur further from the body’s centre of mass resulting in an increase in braking forces. Therefore, it is possible that braking forces were greater during baseline and vest sprinting than sled towing. Further studies that collect force data together with kinematics are needed to confirm these thoughts.
Although thigh angles at foot strike were not significantly different between the two training modalities, thigh angles at toe-off were significantly smaller (i.e. greater thigh extension) during sled towing than during vest sprinting. Several authors have commented that thigh extension provides the most significant propulsive forces during sprinting (Jonhagen, Nemeth, and Eriksson, 1994; Mann, 1981; Wiemann and Tidow, 1995). Whether increased thigh extension during the stance phase is desirable during sprinting is a point of much debate. Mann and Herman (1985) suggested that an abbreviated thigh extension is more desirable, as the increased ground contact required to increase thigh extension and subsequent increase in stance phase duration has a negative impact on step frequency. Interestingly in the current study, increased stance phase duration was found during sled towing. Other authors (Hay, 1985; Vonstein, 1996) have suggested that maximum thigh extension during ground support will increase propulsive forces thus increasing step length, and is therefore a desirable characteristic in sprint technique.
Sled towing resulted in significantly greater knee angles (i.e. less extension, greater flexion) at foot strike compared with baseline and vest sprinting at all stages of the 30-m sprint. Therefore, during sled towing there was greater knee flexion at foot strike and no change in extension at toe-off. This suggests that during sled towing propulsive forces may act through a greater range, and possibly comprise a greater proportion of the stance phase. Ito and colleagues (Ito, Komi, Sjoden, Bosco, and Karlsson,1983) suggested that during the stance phase of running, the most significant braking forces are associated with eccentric contraction of the knee extensors and ankle plantar flexors. In the current study, at both 5 and 15m from the start, sled towing resulted in limited additional knee flexion after foot strike (during the braking phase of stance). At 25m from the start there was an increase in knee flexion after foot strike, but only with the 15% of body mass load. Given that braking forces after foot strike are associated with knee flexion, its absence during sled towing may also indicate kinetic changes that warrant further investigation.
Although not the main focus of this study, it is of interest for future research to examine how the point of attachment or direction of resistance forces from vest or sled could influence the alterations of sprint kinematics. In sled towing, the length of the rope as well as the height of the rope attachment on an athlete (e.g. waist belt vs. shoulder harness) could change the angle of pull. In vest sprinting, the distribution of added weights could influence the position of the centre of mass. Such factors are likely to influence acute sprint kinematics and loading patterns, and may have potential implication for long-term training adaptations.
Conclusion
Sled towing and vest sprinting both resulted in acute changes in sprint kinematics during the acceleration phase of sprinting, but in a different manner when the same relative load (% of body mass) was added. These acute kinematic differences may reflect the different manner in which the two techniques overload the body and therefore provide insight into possible differential mechanisms by which vest and sled towing may act to improve sprint acceleration performance. Vest sprinting has less of an effect on trunk angle, with the athlete remaining more upright, and consequently long-term changes in sprint techniques are less likely. Furthermore, vest sprinting may result in a greater load on the eccentric braking phase at the beginning of the stance phase. As braking forces are a more significant component of the stance phase during the maximum speed phase of sprinting, it seems that vest sprinting may be a more appropriate mode of resistance training for the latter stages of the acceleration phase and the maximum speed phase. Sled towing resulted in greater thigh extension and trunk lean, enabling the athletes to place themselves in an optimal position to maximize propulsive and minimize braking forces. Furthermore, as the duration of the propulsive phase is greater during the stance phase of acceleration, sled towing may be a more appropriate training modality for the early stages of the acceleration phase of sprinting.
Sprint running has been described as consisting of an acceleration phase, a maximum speed phase, and a deceleration phase. In sporting activities such as soccer, rugby, and football, sprint efforts are typically of short duration (e.g. 10–20m) (Spencer, Bishop, Dawson, and Goodman,2005). Therefore, the ability to develop maximal sprint speed in as short a time as possible (i.e. acceleration) may be of greatest significance in those sporting activities (Cronin and Hansen, 2006). Hay (1985) supported such a contention stating that, in many sporting activities, the success enjoyed by athletes is directly related to their ability to increase or decrease their speed rapidly.
An athlete’s ability to accelerate is dependent upon various factors, including technique (kinematics) and the force production capability (kinetics) of the body, in particular the lower limb musculature. Examples of kinematic factors that are considered important to sprint acceleration performance include step frequency and step length (Hunter, Marshall, and McNair, 2004), the duration of the stance phase, the position of foot strike relative to a vertical line through the athlete’s centre of mass, knee flexion angle at and immediately after footstrike, the magnitude of hip extension at toe-off, and the angle of take-off of the athlete’s centre of mass at toe-off. Examples of kinetic factors that are considered important to sprint acceleration performance include horizontal propulsive impulse of the ground reaction force.
Procedures
Sprint times for 10 and 30m were recorded for all runs filmed. Testing consisted of videoing (sagittal plane) athletes sprinting over a distance of 30m, from a standing start. Baseline film of an unresisted 30-m sprint was collected first to provide a baseline measure of sprint kinematics. Athletes were then filmed with two different loads (15% and 20% of body mass) wearing the vest, and with two different loads (15% and 20% of bodymass) towing a sled. Each athlete was therefore tested a total of five times (once for each condition) with 8-min rests between trials; the order of resisted conditions was randomized to avoid any test order bias. The load of 15% of body mass was chosen as it is commonly used for vest sprinting and sled towing, whereas the load of 20% was chosen to examine the effect of a heavier external load on sprint kinematics. Starting position for all sprints was standardized with athletes starting with the left foot forward. The left toe was placed 0.5m behind the starting line. The right toe was placed approximately level with the heel of the left foot.
Data analysis
The kinematics examined can be divided into two categories: step variables and joint angles. Step variables included step length (point of foot strike of one foot to the point of foot strike of the contralateral foot), step frequency (number of steps per second), stance phase duration (the time spent on the ground during each step), and swing phase duration (the time that the foot was not in contact with the ground). The joint kinematics examined included trunk, thigh, knee, and ankle joint angles at the beginning and at the end of the stance phase (i.e. footstrike and toe-off).
Results
Sprint times
The mean 10-m times ranged from 1.72s to 2.06s. Baseline 10-m times were significantly faster than in all the loaded conditions. Significantly slower 10-m sprint times were found for sled towing at 20% of body mass compared with both vest conditions, and for sled towing at 15% of body mass compared with vest sprinting at 15% of body mass. The differences in 10-m sprint times within the two vest conditions, within the two sled conditions, and between the sled (15% body mass) and vest (20% body mass) were found to be non-significant.
The 30-m times became slower as load increased in both the vest and sled conditions. The mean 30-m times ranged from 4.12s for the baseline sprint to 4.90s when towing a sled loaded at 20% of body mass. Baseline times were significantly faster than in all the loaded conditions. All other comparisons at 30m were found to differ significantly. That is, the heavier loads were slower within conditions and both sled loads were slower than both vest loads at 30m.
A significant training technique–distance effect was also found. The effect of resisted technique was different between 10 and 30m. Sled towing resulted in a greater overall sprint time (by 18.0–22.9%) at 10m compared with vest sprinting (by 7.5-10.0%). The effect of sled towing decreased (by 14.7–18.9%) as distance increased. However, the effect of the vests at both loads increased (by 9.3–11.7%) as distance increased.
Step variables
There was an increase in step length through the acceleration phase of sprinting. Significant technique and distance effects were found for step length. Step length differed significantly between baseline and all loaded conditions at all three distances (5, 15, and 25m). Step length during sled towing at 20% of body mass was significantly different from sled towing at 15% of body mass and both vest loads at all distances.
Significant differences were also observed with step frequency. Significant decreases (by 2.7–6.1%) in step frequency between the baseline sprint and all loaded conditions were found.
Stance phase and swing phase
Stance phase duration and swing phase duration showed a significant distance effect. Mean stance phase duration decreased as the athletes progressed over the 30-m distance. This was coupled with concurrent increases in swing phase duration. The stance phase duration was longer than the swing phase duration in the baseline condition at 5 and 15m but not at 25m. However, for all loaded conditions at all distances, swing phase duration did not exceed stance phase duration.
Stance phase duration and swing phase duration were found to differ significantly across technique. Stance phase duration in all loaded conditions was significantly greater than in the baseline condition at all distances from the start. The 20% of body mass loads with the sled and vest resulted in significantly longer stance phases compared with the sled at 15% of body mass at all distances from the start; however, there was no significant difference between the two vest loads. Swing phase duration was significantly shorter for all conditions compared with baseline values. However, there was a significant difference between the sled at 15% of body mass and vest and sled at 20% of body mass.
Joint kinematics
The trunk angles at foot strike during vest sprinting with 20% of body mass were significantly smaller (i.e. more upright) than those at baseline at all three distances from the start. Trunk angles at both foot strike and toe-off during sled towing with 15% and 20% of body mass were significantly greater than those at baseline and vest sprinting with 15% and 20% of body mass at all three distances from the start.
The thigh angles in sled conditions with both 15% and 20% of body mass at toe-off were significantly smaller (i.e. greater thigh extension) than those in the vest conditions with both 15% and 20% of body mass at all three distances.
Knee angles at foot strike were significantly greater (i.e. greater knee flexion) in both sled conditions than in both vest conditions and the baseline sprint at all three distances from the start. No significant differences were observed between sprint conditions in knee angles at peak flexion and at toe-off.
Ankle angles at foot strike were significantly greater at 15 and 25m from the start than at 5m from the start.
Previous researchers have suggested that resisted sprinting techniques may have both acute and longitudinal effects on sprint technique. In the present study, we found that sled towing and vest sprinting influenced sprint kinematics during the acceleration phase of sprinting and that significant differences exist between the two resisted sprint-training techniques on some kinematic variables. As statistical analysis showed no athlete type effect, these findings can be applied to a variety of populations including athletes participating in team sports (such as rugby union) and both beach and track sprinting.
Sprint times and step variables
The effect of external load on sprint times was significant. Both sled towing and vest sprinting resulted in decreased sprint performance (i.e. increased sprint times of 7–23%) compared with unresisted sprinting in this study. To the authors’ knowledge, this is the first study to report the effect of vest loading on sprint times, whereas previous research has consistently reported decreased sprint performance during sled towing when compared with unresisted sprinting. However, the magnitudes of performance decrements differed across the studies (increases of 9-29%), which can be attributed to the differences in the load added, the sprint distance, the training levels of the athletes, and the design of the towing device used.
A greater effect on performance was observed when towing a sled compared with vest sprinting, when the same relative load was used. This finding is most likely related to the additional force required to overcome the effects of friction between the sled and the track surface. When the athlete attempts to move the sled, the ground exerts a horizontal force on the sled called the “force of static friction”. This frictional force acts in the opposite direction to the applied force; that is, it opposes the force that the athlete is applying. Once this force is overcome (by the athlete exerting a force greater than the force of static friction), the sled will begin to move. Therefore, in the initial stages of the sprint, the performance of the athlete was decreased significantly as he or she attempted to overcome the friction of the sled. Once the force of static friction was overcome, the effect of the towing load was decreased, as indicated by the 18% and 22.9% performance decreases for the 15% of body mass and 20% of body mass loads respectively at 10m, which were greater than the 14.7% and 18.9% decreases observed at 30m. A different pattern was observed during vest sprinting, with the performance decrease being greater at 30m than at 10m (7.5% and 10% decreases at 10m vs. 9.3% and 11.7% at 30m). These results suggest that the athletes had less additional force to overcome in the early stages of the sprint during vest sprinting; however, as they developed speed, the need to control the additional mass around their trunk resulted in decreased performance.
The increased sprint times (decreased sprint speed) during the resisted conditions was predominantly the result of decreased step length, with only small decreases in step frequency. With respect to sled towing, these results are consistent with previous studies, whereas no previous literature could be found regarding changes in step variables during vest sprinting.
Sled towing had a greater effect on step variables than did vest sprinting. However, again this only reached statistical significance when comparing sled towing and vest sprinting at 20% of body mass. The more marked effect of sled towing than vest sprinting on step variables at the same relative load (20% of body mass) was indicative of the extra frictional forces provided by this type of loading technique. It may also be a result of the changes in angle and height of take-off of the body’s centre of mass, which was indicated by joint kinematic data to be significantly adjusted during sled towing. The increased trunk flexion, and the increased thigh and knee extension at toe-off, are likely to have led to an anterior and inferior shift of the athlete’s centre of mass, resulting in lower horizontal trajectory of the athlete’s centre of mass.
Joint kinematics
The effects of the two different resisted sprinting techniques on step variables were very similar. That is, step length and step frequency were decreased while stance phase duration was increased. However, the data related to joint kinematics for the vest and sled conditions were significantly different. Due to the paucity of research into the kinematic effects of sled towing and particularly vest sprinting, very few of these findings have been reported previously.In this study, trunk angles during sled towing were significantly greater than at both baseline and in the vest condition at all distances from the start. This finding is consistent with previous research by Letzelter et al. (1995) and Lockie et al. (2003), who found similar trends of increasing trunk lean as the external load increased during sled towing. As suggested by Lockie et al. (2003) and Cronin and Hansen (2006), such a body position (i.e. large trunk lean) during sled towing seems to be specific to sprint acceleration movements. Therefore, sled towing may have the potential to overload the body in a manner specific to sprint acceleration and may be effective in improving sprint acceleration ability. In fact, a recent study by Zafeiridis et al. (2005) supports this hypothesis by showing that 8 weeks of sled towing improved sprint performance in the acceleration phase (0–20m) but not in the maximum speed phase (20–50m).
Greater trunk angles at foot strike during sled towing may decrease the braking forces associated with landing. A number of authors (Alexander,1989; Hunter et al., 2005; Mann and Herman,1985; Mann et al.,1982) have commented that to minimize the negative effect of horizontal and vertical braking on velocity, foot strike underneath and not in front of the athlete’s centre of mass is preferable during sprinting (i.e. the landing distance is smaller). During sled towing, an increase in trunk angle, without a concurrent increase in thigh flexion, allows foot strike to occur closer to the athlete’s centre of mass, possibly reducing braking and increasing the time for the production of propulsive forces. Similarly, if an athlete runs more upright without a concurrent decrease in thigh flexion at foot strike, foot strike will occur further from the body’s centre of mass resulting in an increase in braking forces. Therefore, it is possible that braking forces were greater during baseline and vest sprinting than sled towing. Further studies that collect force data together with kinematics are needed to confirm these thoughts.
Although thigh angles at foot strike were not significantly different between the two training modalities, thigh angles at toe-off were significantly smaller (i.e. greater thigh extension) during sled towing than during vest sprinting. Several authors have commented that thigh extension provides the most significant propulsive forces during sprinting (Jonhagen, Nemeth, and Eriksson, 1994; Mann, 1981; Wiemann and Tidow, 1995). Whether increased thigh extension during the stance phase is desirable during sprinting is a point of much debate. Mann and Herman (1985) suggested that an abbreviated thigh extension is more desirable, as the increased ground contact required to increase thigh extension and subsequent increase in stance phase duration has a negative impact on step frequency. Interestingly in the current study, increased stance phase duration was found during sled towing. Other authors (Hay, 1985; Vonstein, 1996) have suggested that maximum thigh extension during ground support will increase propulsive forces thus increasing step length, and is therefore a desirable characteristic in sprint technique.
Sled towing resulted in significantly greater knee angles (i.e. less extension, greater flexion) at foot strike compared with baseline and vest sprinting at all stages of the 30-m sprint. Therefore, during sled towing there was greater knee flexion at foot strike and no change in extension at toe-off. This suggests that during sled towing propulsive forces may act through a greater range, and possibly comprise a greater proportion of the stance phase. Ito and colleagues (Ito, Komi, Sjoden, Bosco, and Karlsson,1983) suggested that during the stance phase of running, the most significant braking forces are associated with eccentric contraction of the knee extensors and ankle plantar flexors. In the current study, at both 5 and 15m from the start, sled towing resulted in limited additional knee flexion after foot strike (during the braking phase of stance). At 25m from the start there was an increase in knee flexion after foot strike, but only with the 15% of body mass load. Given that braking forces after foot strike are associated with knee flexion, its absence during sled towing may also indicate kinetic changes that warrant further investigation.
Although not the main focus of this study, it is of interest for future research to examine how the point of attachment or direction of resistance forces from vest or sled could influence the alterations of sprint kinematics. In sled towing, the length of the rope as well as the height of the rope attachment on an athlete (e.g. waist belt vs. shoulder harness) could change the angle of pull. In vest sprinting, the distribution of added weights could influence the position of the centre of mass. Such factors are likely to influence acute sprint kinematics and loading patterns, and may have potential implication for long-term training adaptations.
Conclusion
Sled towing and vest sprinting both resulted in acute changes in sprint kinematics during the acceleration phase of sprinting, but in a different manner when the same relative load (% of body mass) was added. These acute kinematic differences may reflect the different manner in which the two techniques overload the body and therefore provide insight into possible differential mechanisms by which vest and sled towing may act to improve sprint acceleration performance. Vest sprinting has less of an effect on trunk angle, with the athlete remaining more upright, and consequently long-term changes in sprint techniques are less likely. Furthermore, vest sprinting may result in a greater load on the eccentric braking phase at the beginning of the stance phase. As braking forces are a more significant component of the stance phase during the maximum speed phase of sprinting, it seems that vest sprinting may be a more appropriate mode of resistance training for the latter stages of the acceleration phase and the maximum speed phase. Sled towing resulted in greater thigh extension and trunk lean, enabling the athletes to place themselves in an optimal position to maximize propulsive and minimize braking forces. Furthermore, as the duration of the propulsive phase is greater during the stance phase of acceleration, sled towing may be a more appropriate training modality for the early stages of the acceleration phase of sprinting.
Wednesday, July 23, 2008
Resisted Sprint Training for the Acceleration Phase of Sprinting
Strength and Conditioning Journal - August 2006
Volume 28,Number 4,pages 42–51
Sprinting has previously been described as consisting of a series of phases: an acceleration phase from 0 to 10 m, a transition phase, and then a maximum velocity phase from 36 to 100m during a 100-m sprint. Mero et al. described the acceleration phase as being in the first 30–50 m, followed by a maximum velocity phase and a phase of deceleration. However, for many sporting activities such as soccer, rugby, football, netball, and basketball, maximum velocity is not always attained, and repeated short sprints are more common. As such, the ability to develop velocity in as short a time as possible (acceleration) may be of most importance to performance in many sporting activities. Furthermore, it is thought that acceleration and maximum velocity are relatively separate and specific qualities. Therefore, it is the development of the acceleration phase of sprinting that would seem to be of greatest benefit to many sports people and is the subsequent focus of this article.
Biomechanics of the Acceleration Phase
Kinematics
Sprint velocity is a product of step length and step frequency. Step length and step frequency are both increased to enhance velocity during the acceleration phase (see Figure 1) of sprinting. Each step comprises a stance phase and a swing phase. The time that the foot is in contact with the ground during the stride cycle is termed the stance phase, and the swing phase is from ipsilateral foot strike to ipsilateral toe-off. The acceleration phase of sprinting is characterized by a relatively long stance phase as the runner endeavors to generate velocity. The stance phase comprises 2 distinct components, braking and propulsion. The relative contributions of braking and propulsion to the stance phase differ during the acceleration phase of sprinting compared to the maximum velocity phase. During the acceleration phase, the stance phase is largely made up of a propulsive component, with minimal braking forces at foot strike. However, in the maximum velocity phase, braking constitutes up to 43% of the stance phase. Mero found that when the athlete was accelerating, the braking phase constituted only 12.9% of the stance phase, and the remainder was associated with propulsion.
With respect to sprinting technique, the acceleration phase has been found to differ significantly from the maximum velocity phase of sprinting. Mero and colleagues reported that during the first few strides in sprinting, the body’s center of gravity undergoes a posterior shift, from an anterior position at foot strike to a position posterior to the point of foot strike. Seagrave, based on coaching observations, has suggested that during the initial stages of the acceleration phase the body should be at an angle of approximately 45° to the surface of the ground. As the sprinter’s velocity increases, the body becomes more upright.
An athlete’s sprinting technique is determined by the angles of the trunk, thigh, knee, and ankle. There is considerable variation in the literature regarding thigh angle (angle between the thigh segment and a vertical line from the ground) during sprint running. Frishberg reported a foot strike thigh angle of 29.9° at 50 m from a sprint start. In contrast, Letzelter and colleagues reported a mean thigh angle of 22.6°at 30 m from a sprint start. The literature is inconclusive as to whether thigh angle varies considerably between the acceleration and maximum velocity phases of sprinting. Williams in reviewing the literature reported foot-strike thigh angles ranging from 20.8° to 30° and stated that thigh angle did not seem to change appreciably with increasing running speed. There is also variation in the literature regarding optimal thigh angle at toe-off. Mann and Herman stated that more efficient sprinters terminated the nonproductive latter part of the stance phase and began recovery more quickly, whereas Hay believed that the thigh should move through as great a range as possible and that failure of the thigh to do so was a common fault in sprinting.
Knee flexion at foot strike has been reported to range between 10° and 30°. Following foot strike, the knee flexes further to absorb the energy associated with the ground reaction forces generated at foot strike. This flexion following foot strike was reported by Jacobs and colleagues to be on average approximately 15°. Mann and Herman reported a mean foot strike knee angle of 13° 180 m into a 200-m race. This is in contrast to Jacobs and colleagues and Paradisis and Cooke who reported mean foot-strike knee angles of 30° and 35° respectively during the acceleration phase. This suggests that knee flexion at foot strike is greater during the acceleration phase when compared to maximum velocity sprinting. A lack of literature regarding ankle kinematics during sprinting makes comparisons between the acceleration and maximum-velocity phases difficult.
Researchers comparing slow and fast field sport athletes over the first 3 steps of a 15-m sprint found that the fast group had significantly lower (approximately 11-13%) left and right foot contact times, increased stride frequency (approximately 9%), and lower knee extension angles (approximately 11°). It was concluded that those players who were relatively fast during the acceleration phase achieved this by reduced knee extension angles and ground contact times, which increased stride frequency.
Kinetics
Larger propulsive forces (526 N horizontally and 431 N vertically) are exerted during the longer stance phase while accelerating. Horizontal propulsive forces during the first ground contact have been reported to be 46% greater than those observed once maximum velocity is achieved. Vertical propulsive forces have been shown to be similar during the acceleration phase and the maximum velocity phase of sprinting. Braking forces during the acceleration phase have been reported to be relatively small, –153 N horizontally, and a net force of 148 N vertically, compared with –445 N horizontally and 1,707 N vertically during the maximum velocity phase of sprinting. Plamondon and Roy found that vertical braking forces decreased between steps 1 and 12, whereas horizontal braking forces increased up to the 12th stride, where they started to plateau.
EMG Activity
Limited research has been undertaken on the sequencing and degree of muscle activation across the acceleration and maximum speed phases of sprinting. It has been suggested that the hamstrings play an important role during the propulsive phase of stance, extending the thigh. Mero and Komi suggested that knee extensor activity during the propulsive phase of stance during maximum velocity sprinting was limited. However, the propulsive role of the knee extensors during the acceleration phase may be greater. Wieman and Tidow found that during the first few steps of sprinting, the vastus lateralis showed significantly greater activation during the stance phase compared to activity observed at maximum velocity. This increase in vastus lateralis activation was accompanied by a significant decrease in hamstring activation during the stance phase. Harland and Steele also reported an increase in EMG activity of the vastus medialis during the sprint start. These findings suggest that the quadriceps are relatively more important for the acceleration phase as compared to the maximum velocity phase. Delecluse and colleagues stated that although there was still a significant body lean during the acceleration phase, there was less reliance on the stretch-shorten cycle (SSC) and the knee extensors were the main accelerators.
Resisted Sprinting
The preceding literature review has suggested some significant differences between the acceleration and maximum speed phases of sprinting. During the acceleration phase, there is a longer stance phase, greater knee and trunk flexion at foot strike, greater propulsive forces, and possibly greater EMG activity in the knee extensors. It follows that these factors should be taken into consideration when choosing the mode of training for the acceleration phase of sprinting. As such, resisted sprint training has become a popular training method, with many sports teams and track athletes to develop acceleration. It is thought that such techniques increase neural activation and hence muscular force output of the leg, resulting in an increase in stride length over time. However, whether this is actually the case has not been empirically proven. It may be that each of these resisted techniques provides a different training stimulus and therefore each may be better suited for training different phases of sprinting. This contention is discussed in the ensuing sections.
Limb Loading
Limb loading involves the attachment of weights to the extremities of the athlete in order to provide overload while sprinting. The loads are typically placed at the ends of the distal segments and thus are likely to increase the moment of inertia considerably and subsequently increase the muscle activity re-quired during motion. Two studies have examined the effects of limb loading. Ropret et al. studied the effect of arm and leg loading on sprinting velocity, step length, and step frequency. Arm loading up to a maximum of 0.66 kg did not have a significant effect on the athlete’s sprinting velocity, step length, or step frequency. In contrast, leg loading at 0.6, 1.2, and 1.8 kg had a significant effect on performance. A load of 1.8 kg significantly reduced sprinting velocity. Step length remained the same, so the decrease in velocity was attributed to a decrease in step frequency.
Similar findings were reported by Martin, who compared the effects of loading the foot by adding lead to specially developed running shoes and loading the thighs by wearing lead-weighted bike pants during treadmill running. It was found that foot loading and thigh loading lengthened step length, increased recovery time of the contralateral limb, and increased swing phase duration. However, this effect was statistically significant with ankle joint loading only. Therefore, this study illustrated how the increased inertial forces associated with distal loading resulted in a greater effect on running technique, especially in terms of decreasing step frequency.
From these studies it would seem that loading of the distal segment of the lower limb at the ankle joints decreased velocity and that the mechanism of velocity decrease was likely to have been through a decrease in step frequency, whereas step length remained relatively unaffected. To the authors’ knowledge, there are to date no training studies examining the long-term adaptations using this training technique.
Uphill Running
Some practitioners have suggested that uphill running will place increased load on the thigh extensor muscles as athletes try to maximize step length. Because thigh extensor activity is thought to be important in the propulsive phase of sprinting, the associated gain in strength is thought to increase the athlete’s step length when sprinting on a flat surface. Dintiman et al., based on observations, suggested that the hill incline should be at a grade that does not compromise running form. They suggested, based on their training experience, the use of steeper inclines to improve the start and acceleration phases of sprinting (8-10° in 2.5-3.5 seconds) and progressively reduced inclines for longer sprint training.
Kunz and Kaufman concluded that uphill running might result in longitudinal adaptations, increasing step length, and shortening the stance phase during sprinting on a flat surface.
Paradisis and Cooke also compared the kinematics and kinetics of sprinting on a flat surface to sprinting up a 3° slope. It was found that velocity was significantly decreased (3%) when sprinting uphill compared to sprinting on a flat surface. The researchers observed that the decrease in velocity was primarily attributable to a decrease in step length, which decreased by 5.2%. These researchers also found significant changes in body position between sprinting uphill and on a flat surface. Trunk flexion was significantly increased, and the shank angle (the angle between the lower leg and the running surface) was reduced at both foot strike and toe-off. Thigh-to-thigh angle (the angle between the right and left thigh segments) was significantly decreased at foot strike and knee angle was significantly decreased at toe-off. A significant decrease in landing distance (the distance between a vertical line through the athlete’s center of gravity and the point of foot strike) was also noted. Paradisis and Cooke suggested that these kinematic changes resulted in an increase in the contribution of the propulsive phase to the stance phase during uphill sprinting. Once more, the long-term application of such training has not been investigated.
Weighted Vests
The use of weighted vests while sprinting is another method of providing resistance during training. Vest sprinting with loads of 15 and 20% of body mass has increased sprint times at 10 m (7.5 and 10%, respectively) and at 30 m (9.3 and 11.7%, respectively). It was suggested that the athletes had less additional force to overcome in the early stages of the sprint during vest sprinting, but that as they developed velocity, the need to control the additional mass around the trunk resulted in decreased performance. The increase in sprint times was attributed to decreased step length and step frequency and to increased stance times. However, the joint kinematics was similar between loaded and unloaded conditions.
A series of longitudinal studies have investigated the practice of applying extra mass to the body of elite athletes for prolonged periods of time. The first in this series of investigations attempted to create a “hypergravity” situation by loading the athlete for a 3-week period with a vest that equated to 13% of the athlete’s body mass. The load was worn from morning to evening, including training sessions. Training included jump training and weight training that did not deviate from normal training for the 3-week trial period other than by the additional load of the weighted vest. Following training, a significant increase in lower limb explosive power measured during squat jumps and drop jumps (approximately 10%) was found. Furthermore, a significant right shift of the force-velocity curve measured during squat jumping was observed. It was concluded that the high-gravity conditions influenced the muscle mechanics of even well-trained athletes.
Bosco examined the force-velocity relationship of the lower limb musculature in 5 international-level male jumpers over a 13-month period. During the first 12 months of training, in which the athletes did not wear vests, no improvements in the measured variables were found. However, after 3 weeks of a simulated hypergravity situation in which the athlete wore 11% of his body mass, a significant shift of the force-velocity curve to the right was observed during loaded squat jump assessment. The utilization of the weighted vest also resulted in an increase in average drop jump performance from 0.48 m to 0.55 m. Bosco did not examine whether the mechanisms behind the improvements found were neural or muscular. However, it was noted that after the high-gravity conditioning, execution time for the SSC during drop jumping and 15-second jumps was decreased, and force development was improved. Both of these tests assessed fast SSC movements as found during sprint running. Bosco suggested that this improvement in fast SSC performance might be a result of increased stiffness of the leg extensor musculature.
Another study by Bosco and colleagues further investigated the effects of vest training by using sprinters performing jump and sprint training with a load of 7-8% of their body mass. As in previous studies, the athletes wore the extra load for 3 weeks from morning until evening, including during training times. Normal training volumes were otherwise unchanged. As found in previous studies, the force-velocity curve was observed to shift to the right. Therefore, the ability of those subjects who wore vests to produce greater force at higher velocities dramatically improved with this form of conditioning. No significant changes were found in the control group.
Bosco and colleagues did not study factors related to sprint mechanics or sprint performance. However, it is possible that a vest worn during sprinting might increase the vertical force at each ground contact, thereby increasing the eccentric load on the extensor muscles during the braking phase. This effect may serve to increase the muscles’ capacity to store elastic energy and improve power output.
Resisted Towing
The towing of weighted devices such as sleds and tires is the most common method of providing towing resistance for the enhancement of sprint performance, although the use of parachutes has also been documented. Faccioni, again based on coaching observations, suggested that using towing as a form of resistance may increase the load on the athlete’s torso and therefore may require more stabilization. This training stimulus may increase pelvic stabilization, which may have a positive effect on sprint performance.
Letzelter et al. studied the acute effect that different loads had on performance variables with a group of female sprinters during sled towing. They found that a 2.5-kg load resulted in an 8% decrease in performance over 30 m, and 10 kg resulted in a 22% decrease in sprint performance. Step length was affected to a far greater extent than step frequency by the increased resistance. As the load increased, decreasing step length accounted for a greater proportion of decreasing velocity. The variable affected most by increasing resistance was stance phase duration, which increased significantly with all loads. Increased loads also caused increased upper-body lean and increased thigh angle at both the beginning and the end of the stance phase. This increased thigh angle reflects the increased need for force production during the prolonged stance phase. Unfortunately, this study did not quantify towing loads relative to body mass or provide anthropometric data on the subjects. It is therefore difficult to relate the results found to previously recommended loading guidelines.
Lockie et al. studied the effect of sled towing on acceleration-phase sprinting kinematics in field-sport athletes. Athletes towed weighted sleds with loads equaling 12.6 and 32.2% of their body mass over a 15-m distance. Sled towing resulted in a decrease in stride length of 10 and 24% for the 12.6 and 32.2% loads respectively. Stride frequency was significantly decreased compared to baseline with both towing loads, but there was no significant difference between the 2 towing loads. The duration of the stance phase was also significantly increased during the towing conditions. Trunk flexion and hip range of motion were also significantly increased compared to baseline with both towing loads. Knee joint range of motion was increased for load 1 only on stride 1 of the sprint. The authors concluded that the heavier load led to a greater disruption of running kinematics, and recommended training with lighter loads.
Kafer and colleagues studied the effects of resisted and assisted training on sprint times over 20-, 40-, and 60-m distances. A weighted sled was used to provide resistance, and a bungee cord (rubber rope) to provide assistance. The training groups included an assisted group, a resisted group, a group combining the 2 techniques, and a control group performing unloaded sprint training. The resisted group recorded an average improvement of 0.08 seconds and 0.35 seconds in sprint times over 20- and 60-m distances respectively. The combined group was significantly faster posttraining over both 40 m (0.19 seconds) and 60 m (0.34 seconds). The control group and the assisted group displayed significant improvements between pretraining and posttraining only over 60 m (0.08 and 0.27 seconds, respectively). It was suggested that the generic improvements in 60-m sprint performance were attributable to the subjects’ being rugby union players, who were unfamiliar with running the longer distances that are required only occasionally in their sport. Between group comparisons showed that only the combined resisted-assisted group was significantly faster than the control group posttraining. The mechanisms behind improvements in performance were not investigated. It was suggested, however, that a possible reason for the improvement was that the increased resistance from the sled resulted in increased force production to develop and maintain velocity. The researchers speculated that this effect would increase the load associated with the SSC, increasing muscle stiffness and vertical force at each ground contact. Further research examining mechanical adaptations with resisted towing is required in order to examine mechanisms behind any improvements in sprinting performance.
In terms of the loading parameters, towing loads of less than 10% of body mass have been recommended, but this is based on practical observations rather than research. Kafer and colleagues suggested that a load less than 15% of the athlete’s body mass will not affect the sprinter’s technique, but they also stated that the evidence was anecdotal and not scientifically substantiated. Seagrave believed that the load should be determined by the extent to which performance is affected. If performance variables decrease by more than 10%, the load being used is too great and will have a detrimental effect on sprinting technique.
Frictional forces contribute to the resistance experienced by the athlete when towing a sled. It is difficult to quantify these frictional forces. The magnitude of the frictional force (coefficient of friction) is dependent on the mass on the sled and on the characteristics of the ground surface and the sled. It is relatively independent of the total surface area and is also independent at velocities between 0.01 and several m/s. For training purposes, the load on the sled and the surface over which it is moving will be the variables that can be most easily manipulated to change the frictional force and hence the resistance against which the athlete is working. Therefore, when assigning load during sled towing, coaches not only must be conscious of how much mass they are adding to the sled, but also must be aware of the characteristics of the surface on which they are towing. For example, towing on grass is likely to result in a different coefficient of kinetic friction from towing on a track. Furthermore, James has shown that the coefficient of kinetic friction was less for wet steel than for dry steel. The same is likely to be the case for a track surface with a decrease in frictional force when towing on a wet track.
It is possible that during resisted sprinting, different loads could be used for training the different phases of the sprint. It has been suggested that greater resistance should be used for training the acceleration phase and light loads for increasing the maximum velocity phase. Increased loads that increase forward body lean and increase stance phase duration may be beneficial to the acceleration phase of sprinting. However, there is a lack of information on the kinematic, kinetic, and EMG differences between loading parameters and their effects. Therefore, these thoughts are also based on anecdotal evidence.
Practical Applications for Resisted Sprinting
As described previously, different phases of the sprint generate different kinematic, kinetic, and EMG responses. The acceleration phase, for example, is characterized by a longer stance phase, a large proportion of which is propulsion. During the acceleration phase, there is greater trunk flexion, greater knee flexion at foot strike, and greater recruitment of the knee extensor musculature. Taking into consideration the principle of specificity in strength and power training, it follows that those modes of training that replicate these characteristics should be utilized. It is clear that different resistance training methods overload the body in a different manner, and therefore the training effect provided by each of the resisted training techniques results in a specific adaptation.
One method of providing this specificity in resistance training is to add load to the athlete while sprinting. The adjustments in sprinting technique made during towing and uphill running seem to replicate the acceleration phase more closely than do other resisted techniques. Both these techniques increase trunk lean, stance duration, and the need for horizontal force production during the propulsive phase of stance. Hill sprinting will also increase the need for horizontal propulsive forces, although the need to counter the grade may also result in an increased need for vertical propulsion. The specific need for increased propulsive forces may make modes of resistance such as resisted towing and hill sprinting more appropriate for training the acceleration phase of sprinting, in which propulsive force production comprises a large proportion of the
stance phase.
Weighted vests provide overload in a different manner, by increasing the vertical load during foot strike, increasing the braking forces, and perhaps overloading the SSC to better effect. As such, weighted-vest training may have better applications for maximum velocity adaptation. Nonetheless, such training may also have an application to the training of the acceleration phase of sprinting by increasing eccentric strength and muscle stiffness and therefore decreasing the duration of the stance phase. It is not clear whether this type of overload or the greater horizontal overload provided by resisted towing results in greater increases in acceleration phase performance. Likewise, the optimal load to be used during resisted sprinting has not been determined. That is, it may be that greater resistance should be used for training the acceleration phase and light loads for increasing the maximum velocity phase. However, the practitioner should be aware that there is a risk that too much load may result in technique adjustments that could compromise the athlete’s sprinting technique.
Resisted sprinting provides a highly specific and convenient method of training muscular power for the acceleration phase of sprinting. Table 1 attempts to summarize some of the information into a format that may assist the training of athletes. However, the reader needs to be mindful that most evidence in this area is anecdotal, with very few randomized controlled designs validating the most desirable mode of resistance training, the mechanisms behind improvements in the acceleration phase, the possible negative effect on technique, and the optimal training loads. Answers to these questions are necessary if resisted sprinting is to be utilized effectively by coaches and athletes.
Volume 28,Number 4,pages 42–51
Sprinting has previously been described as consisting of a series of phases: an acceleration phase from 0 to 10 m, a transition phase, and then a maximum velocity phase from 36 to 100m during a 100-m sprint. Mero et al. described the acceleration phase as being in the first 30–50 m, followed by a maximum velocity phase and a phase of deceleration. However, for many sporting activities such as soccer, rugby, football, netball, and basketball, maximum velocity is not always attained, and repeated short sprints are more common. As such, the ability to develop velocity in as short a time as possible (acceleration) may be of most importance to performance in many sporting activities. Furthermore, it is thought that acceleration and maximum velocity are relatively separate and specific qualities. Therefore, it is the development of the acceleration phase of sprinting that would seem to be of greatest benefit to many sports people and is the subsequent focus of this article.
Biomechanics of the Acceleration Phase
Kinematics
Sprint velocity is a product of step length and step frequency. Step length and step frequency are both increased to enhance velocity during the acceleration phase (see Figure 1) of sprinting. Each step comprises a stance phase and a swing phase. The time that the foot is in contact with the ground during the stride cycle is termed the stance phase, and the swing phase is from ipsilateral foot strike to ipsilateral toe-off. The acceleration phase of sprinting is characterized by a relatively long stance phase as the runner endeavors to generate velocity. The stance phase comprises 2 distinct components, braking and propulsion. The relative contributions of braking and propulsion to the stance phase differ during the acceleration phase of sprinting compared to the maximum velocity phase. During the acceleration phase, the stance phase is largely made up of a propulsive component, with minimal braking forces at foot strike. However, in the maximum velocity phase, braking constitutes up to 43% of the stance phase. Mero found that when the athlete was accelerating, the braking phase constituted only 12.9% of the stance phase, and the remainder was associated with propulsion.
With respect to sprinting technique, the acceleration phase has been found to differ significantly from the maximum velocity phase of sprinting. Mero and colleagues reported that during the first few strides in sprinting, the body’s center of gravity undergoes a posterior shift, from an anterior position at foot strike to a position posterior to the point of foot strike. Seagrave, based on coaching observations, has suggested that during the initial stages of the acceleration phase the body should be at an angle of approximately 45° to the surface of the ground. As the sprinter’s velocity increases, the body becomes more upright.
An athlete’s sprinting technique is determined by the angles of the trunk, thigh, knee, and ankle. There is considerable variation in the literature regarding thigh angle (angle between the thigh segment and a vertical line from the ground) during sprint running. Frishberg reported a foot strike thigh angle of 29.9° at 50 m from a sprint start. In contrast, Letzelter and colleagues reported a mean thigh angle of 22.6°at 30 m from a sprint start. The literature is inconclusive as to whether thigh angle varies considerably between the acceleration and maximum velocity phases of sprinting. Williams in reviewing the literature reported foot-strike thigh angles ranging from 20.8° to 30° and stated that thigh angle did not seem to change appreciably with increasing running speed. There is also variation in the literature regarding optimal thigh angle at toe-off. Mann and Herman stated that more efficient sprinters terminated the nonproductive latter part of the stance phase and began recovery more quickly, whereas Hay believed that the thigh should move through as great a range as possible and that failure of the thigh to do so was a common fault in sprinting.
Knee flexion at foot strike has been reported to range between 10° and 30°. Following foot strike, the knee flexes further to absorb the energy associated with the ground reaction forces generated at foot strike. This flexion following foot strike was reported by Jacobs and colleagues to be on average approximately 15°. Mann and Herman reported a mean foot strike knee angle of 13° 180 m into a 200-m race. This is in contrast to Jacobs and colleagues and Paradisis and Cooke who reported mean foot-strike knee angles of 30° and 35° respectively during the acceleration phase. This suggests that knee flexion at foot strike is greater during the acceleration phase when compared to maximum velocity sprinting. A lack of literature regarding ankle kinematics during sprinting makes comparisons between the acceleration and maximum-velocity phases difficult.
Researchers comparing slow and fast field sport athletes over the first 3 steps of a 15-m sprint found that the fast group had significantly lower (approximately 11-13%) left and right foot contact times, increased stride frequency (approximately 9%), and lower knee extension angles (approximately 11°). It was concluded that those players who were relatively fast during the acceleration phase achieved this by reduced knee extension angles and ground contact times, which increased stride frequency.
Kinetics
Larger propulsive forces (526 N horizontally and 431 N vertically) are exerted during the longer stance phase while accelerating. Horizontal propulsive forces during the first ground contact have been reported to be 46% greater than those observed once maximum velocity is achieved. Vertical propulsive forces have been shown to be similar during the acceleration phase and the maximum velocity phase of sprinting. Braking forces during the acceleration phase have been reported to be relatively small, –153 N horizontally, and a net force of 148 N vertically, compared with –445 N horizontally and 1,707 N vertically during the maximum velocity phase of sprinting. Plamondon and Roy found that vertical braking forces decreased between steps 1 and 12, whereas horizontal braking forces increased up to the 12th stride, where they started to plateau.
EMG Activity
Limited research has been undertaken on the sequencing and degree of muscle activation across the acceleration and maximum speed phases of sprinting. It has been suggested that the hamstrings play an important role during the propulsive phase of stance, extending the thigh. Mero and Komi suggested that knee extensor activity during the propulsive phase of stance during maximum velocity sprinting was limited. However, the propulsive role of the knee extensors during the acceleration phase may be greater. Wieman and Tidow found that during the first few steps of sprinting, the vastus lateralis showed significantly greater activation during the stance phase compared to activity observed at maximum velocity. This increase in vastus lateralis activation was accompanied by a significant decrease in hamstring activation during the stance phase. Harland and Steele also reported an increase in EMG activity of the vastus medialis during the sprint start. These findings suggest that the quadriceps are relatively more important for the acceleration phase as compared to the maximum velocity phase. Delecluse and colleagues stated that although there was still a significant body lean during the acceleration phase, there was less reliance on the stretch-shorten cycle (SSC) and the knee extensors were the main accelerators.
Resisted Sprinting
The preceding literature review has suggested some significant differences between the acceleration and maximum speed phases of sprinting. During the acceleration phase, there is a longer stance phase, greater knee and trunk flexion at foot strike, greater propulsive forces, and possibly greater EMG activity in the knee extensors. It follows that these factors should be taken into consideration when choosing the mode of training for the acceleration phase of sprinting. As such, resisted sprint training has become a popular training method, with many sports teams and track athletes to develop acceleration. It is thought that such techniques increase neural activation and hence muscular force output of the leg, resulting in an increase in stride length over time. However, whether this is actually the case has not been empirically proven. It may be that each of these resisted techniques provides a different training stimulus and therefore each may be better suited for training different phases of sprinting. This contention is discussed in the ensuing sections.
Limb Loading
Limb loading involves the attachment of weights to the extremities of the athlete in order to provide overload while sprinting. The loads are typically placed at the ends of the distal segments and thus are likely to increase the moment of inertia considerably and subsequently increase the muscle activity re-quired during motion. Two studies have examined the effects of limb loading. Ropret et al. studied the effect of arm and leg loading on sprinting velocity, step length, and step frequency. Arm loading up to a maximum of 0.66 kg did not have a significant effect on the athlete’s sprinting velocity, step length, or step frequency. In contrast, leg loading at 0.6, 1.2, and 1.8 kg had a significant effect on performance. A load of 1.8 kg significantly reduced sprinting velocity. Step length remained the same, so the decrease in velocity was attributed to a decrease in step frequency.
Similar findings were reported by Martin, who compared the effects of loading the foot by adding lead to specially developed running shoes and loading the thighs by wearing lead-weighted bike pants during treadmill running. It was found that foot loading and thigh loading lengthened step length, increased recovery time of the contralateral limb, and increased swing phase duration. However, this effect was statistically significant with ankle joint loading only. Therefore, this study illustrated how the increased inertial forces associated with distal loading resulted in a greater effect on running technique, especially in terms of decreasing step frequency.
From these studies it would seem that loading of the distal segment of the lower limb at the ankle joints decreased velocity and that the mechanism of velocity decrease was likely to have been through a decrease in step frequency, whereas step length remained relatively unaffected. To the authors’ knowledge, there are to date no training studies examining the long-term adaptations using this training technique.
Uphill Running
Some practitioners have suggested that uphill running will place increased load on the thigh extensor muscles as athletes try to maximize step length. Because thigh extensor activity is thought to be important in the propulsive phase of sprinting, the associated gain in strength is thought to increase the athlete’s step length when sprinting on a flat surface. Dintiman et al., based on observations, suggested that the hill incline should be at a grade that does not compromise running form. They suggested, based on their training experience, the use of steeper inclines to improve the start and acceleration phases of sprinting (8-10° in 2.5-3.5 seconds) and progressively reduced inclines for longer sprint training.
Kunz and Kaufman concluded that uphill running might result in longitudinal adaptations, increasing step length, and shortening the stance phase during sprinting on a flat surface.
Paradisis and Cooke also compared the kinematics and kinetics of sprinting on a flat surface to sprinting up a 3° slope. It was found that velocity was significantly decreased (3%) when sprinting uphill compared to sprinting on a flat surface. The researchers observed that the decrease in velocity was primarily attributable to a decrease in step length, which decreased by 5.2%. These researchers also found significant changes in body position between sprinting uphill and on a flat surface. Trunk flexion was significantly increased, and the shank angle (the angle between the lower leg and the running surface) was reduced at both foot strike and toe-off. Thigh-to-thigh angle (the angle between the right and left thigh segments) was significantly decreased at foot strike and knee angle was significantly decreased at toe-off. A significant decrease in landing distance (the distance between a vertical line through the athlete’s center of gravity and the point of foot strike) was also noted. Paradisis and Cooke suggested that these kinematic changes resulted in an increase in the contribution of the propulsive phase to the stance phase during uphill sprinting. Once more, the long-term application of such training has not been investigated.
Weighted Vests
The use of weighted vests while sprinting is another method of providing resistance during training. Vest sprinting with loads of 15 and 20% of body mass has increased sprint times at 10 m (7.5 and 10%, respectively) and at 30 m (9.3 and 11.7%, respectively). It was suggested that the athletes had less additional force to overcome in the early stages of the sprint during vest sprinting, but that as they developed velocity, the need to control the additional mass around the trunk resulted in decreased performance. The increase in sprint times was attributed to decreased step length and step frequency and to increased stance times. However, the joint kinematics was similar between loaded and unloaded conditions.
A series of longitudinal studies have investigated the practice of applying extra mass to the body of elite athletes for prolonged periods of time. The first in this series of investigations attempted to create a “hypergravity” situation by loading the athlete for a 3-week period with a vest that equated to 13% of the athlete’s body mass. The load was worn from morning to evening, including training sessions. Training included jump training and weight training that did not deviate from normal training for the 3-week trial period other than by the additional load of the weighted vest. Following training, a significant increase in lower limb explosive power measured during squat jumps and drop jumps (approximately 10%) was found. Furthermore, a significant right shift of the force-velocity curve measured during squat jumping was observed. It was concluded that the high-gravity conditions influenced the muscle mechanics of even well-trained athletes.
Bosco examined the force-velocity relationship of the lower limb musculature in 5 international-level male jumpers over a 13-month period. During the first 12 months of training, in which the athletes did not wear vests, no improvements in the measured variables were found. However, after 3 weeks of a simulated hypergravity situation in which the athlete wore 11% of his body mass, a significant shift of the force-velocity curve to the right was observed during loaded squat jump assessment. The utilization of the weighted vest also resulted in an increase in average drop jump performance from 0.48 m to 0.55 m. Bosco did not examine whether the mechanisms behind the improvements found were neural or muscular. However, it was noted that after the high-gravity conditioning, execution time for the SSC during drop jumping and 15-second jumps was decreased, and force development was improved. Both of these tests assessed fast SSC movements as found during sprint running. Bosco suggested that this improvement in fast SSC performance might be a result of increased stiffness of the leg extensor musculature.
Another study by Bosco and colleagues further investigated the effects of vest training by using sprinters performing jump and sprint training with a load of 7-8% of their body mass. As in previous studies, the athletes wore the extra load for 3 weeks from morning until evening, including during training times. Normal training volumes were otherwise unchanged. As found in previous studies, the force-velocity curve was observed to shift to the right. Therefore, the ability of those subjects who wore vests to produce greater force at higher velocities dramatically improved with this form of conditioning. No significant changes were found in the control group.
Bosco and colleagues did not study factors related to sprint mechanics or sprint performance. However, it is possible that a vest worn during sprinting might increase the vertical force at each ground contact, thereby increasing the eccentric load on the extensor muscles during the braking phase. This effect may serve to increase the muscles’ capacity to store elastic energy and improve power output.
Resisted Towing
The towing of weighted devices such as sleds and tires is the most common method of providing towing resistance for the enhancement of sprint performance, although the use of parachutes has also been documented. Faccioni, again based on coaching observations, suggested that using towing as a form of resistance may increase the load on the athlete’s torso and therefore may require more stabilization. This training stimulus may increase pelvic stabilization, which may have a positive effect on sprint performance.
Letzelter et al. studied the acute effect that different loads had on performance variables with a group of female sprinters during sled towing. They found that a 2.5-kg load resulted in an 8% decrease in performance over 30 m, and 10 kg resulted in a 22% decrease in sprint performance. Step length was affected to a far greater extent than step frequency by the increased resistance. As the load increased, decreasing step length accounted for a greater proportion of decreasing velocity. The variable affected most by increasing resistance was stance phase duration, which increased significantly with all loads. Increased loads also caused increased upper-body lean and increased thigh angle at both the beginning and the end of the stance phase. This increased thigh angle reflects the increased need for force production during the prolonged stance phase. Unfortunately, this study did not quantify towing loads relative to body mass or provide anthropometric data on the subjects. It is therefore difficult to relate the results found to previously recommended loading guidelines.
Lockie et al. studied the effect of sled towing on acceleration-phase sprinting kinematics in field-sport athletes. Athletes towed weighted sleds with loads equaling 12.6 and 32.2% of their body mass over a 15-m distance. Sled towing resulted in a decrease in stride length of 10 and 24% for the 12.6 and 32.2% loads respectively. Stride frequency was significantly decreased compared to baseline with both towing loads, but there was no significant difference between the 2 towing loads. The duration of the stance phase was also significantly increased during the towing conditions. Trunk flexion and hip range of motion were also significantly increased compared to baseline with both towing loads. Knee joint range of motion was increased for load 1 only on stride 1 of the sprint. The authors concluded that the heavier load led to a greater disruption of running kinematics, and recommended training with lighter loads.
Kafer and colleagues studied the effects of resisted and assisted training on sprint times over 20-, 40-, and 60-m distances. A weighted sled was used to provide resistance, and a bungee cord (rubber rope) to provide assistance. The training groups included an assisted group, a resisted group, a group combining the 2 techniques, and a control group performing unloaded sprint training. The resisted group recorded an average improvement of 0.08 seconds and 0.35 seconds in sprint times over 20- and 60-m distances respectively. The combined group was significantly faster posttraining over both 40 m (0.19 seconds) and 60 m (0.34 seconds). The control group and the assisted group displayed significant improvements between pretraining and posttraining only over 60 m (0.08 and 0.27 seconds, respectively). It was suggested that the generic improvements in 60-m sprint performance were attributable to the subjects’ being rugby union players, who were unfamiliar with running the longer distances that are required only occasionally in their sport. Between group comparisons showed that only the combined resisted-assisted group was significantly faster than the control group posttraining. The mechanisms behind improvements in performance were not investigated. It was suggested, however, that a possible reason for the improvement was that the increased resistance from the sled resulted in increased force production to develop and maintain velocity. The researchers speculated that this effect would increase the load associated with the SSC, increasing muscle stiffness and vertical force at each ground contact. Further research examining mechanical adaptations with resisted towing is required in order to examine mechanisms behind any improvements in sprinting performance.
In terms of the loading parameters, towing loads of less than 10% of body mass have been recommended, but this is based on practical observations rather than research. Kafer and colleagues suggested that a load less than 15% of the athlete’s body mass will not affect the sprinter’s technique, but they also stated that the evidence was anecdotal and not scientifically substantiated. Seagrave believed that the load should be determined by the extent to which performance is affected. If performance variables decrease by more than 10%, the load being used is too great and will have a detrimental effect on sprinting technique.
Frictional forces contribute to the resistance experienced by the athlete when towing a sled. It is difficult to quantify these frictional forces. The magnitude of the frictional force (coefficient of friction) is dependent on the mass on the sled and on the characteristics of the ground surface and the sled. It is relatively independent of the total surface area and is also independent at velocities between 0.01 and several m/s. For training purposes, the load on the sled and the surface over which it is moving will be the variables that can be most easily manipulated to change the frictional force and hence the resistance against which the athlete is working. Therefore, when assigning load during sled towing, coaches not only must be conscious of how much mass they are adding to the sled, but also must be aware of the characteristics of the surface on which they are towing. For example, towing on grass is likely to result in a different coefficient of kinetic friction from towing on a track. Furthermore, James has shown that the coefficient of kinetic friction was less for wet steel than for dry steel. The same is likely to be the case for a track surface with a decrease in frictional force when towing on a wet track.
It is possible that during resisted sprinting, different loads could be used for training the different phases of the sprint. It has been suggested that greater resistance should be used for training the acceleration phase and light loads for increasing the maximum velocity phase. Increased loads that increase forward body lean and increase stance phase duration may be beneficial to the acceleration phase of sprinting. However, there is a lack of information on the kinematic, kinetic, and EMG differences between loading parameters and their effects. Therefore, these thoughts are also based on anecdotal evidence.
Practical Applications for Resisted Sprinting
As described previously, different phases of the sprint generate different kinematic, kinetic, and EMG responses. The acceleration phase, for example, is characterized by a longer stance phase, a large proportion of which is propulsion. During the acceleration phase, there is greater trunk flexion, greater knee flexion at foot strike, and greater recruitment of the knee extensor musculature. Taking into consideration the principle of specificity in strength and power training, it follows that those modes of training that replicate these characteristics should be utilized. It is clear that different resistance training methods overload the body in a different manner, and therefore the training effect provided by each of the resisted training techniques results in a specific adaptation.
One method of providing this specificity in resistance training is to add load to the athlete while sprinting. The adjustments in sprinting technique made during towing and uphill running seem to replicate the acceleration phase more closely than do other resisted techniques. Both these techniques increase trunk lean, stance duration, and the need for horizontal force production during the propulsive phase of stance. Hill sprinting will also increase the need for horizontal propulsive forces, although the need to counter the grade may also result in an increased need for vertical propulsion. The specific need for increased propulsive forces may make modes of resistance such as resisted towing and hill sprinting more appropriate for training the acceleration phase of sprinting, in which propulsive force production comprises a large proportion of the
stance phase.
Weighted vests provide overload in a different manner, by increasing the vertical load during foot strike, increasing the braking forces, and perhaps overloading the SSC to better effect. As such, weighted-vest training may have better applications for maximum velocity adaptation. Nonetheless, such training may also have an application to the training of the acceleration phase of sprinting by increasing eccentric strength and muscle stiffness and therefore decreasing the duration of the stance phase. It is not clear whether this type of overload or the greater horizontal overload provided by resisted towing results in greater increases in acceleration phase performance. Likewise, the optimal load to be used during resisted sprinting has not been determined. That is, it may be that greater resistance should be used for training the acceleration phase and light loads for increasing the maximum velocity phase. However, the practitioner should be aware that there is a risk that too much load may result in technique adjustments that could compromise the athlete’s sprinting technique.
Resisted sprinting provides a highly specific and convenient method of training muscular power for the acceleration phase of sprinting. Table 1 attempts to summarize some of the information into a format that may assist the training of athletes. However, the reader needs to be mindful that most evidence in this area is anecdotal, with very few randomized controlled designs validating the most desirable mode of resistance training, the mechanisms behind improvements in the acceleration phase, the possible negative effect on technique, and the optimal training loads. Answers to these questions are necessary if resisted sprinting is to be utilized effectively by coaches and athletes.
Saturday, July 12, 2008
Resisted Sprint Training
Effects of weighted vests and sled towing on sprint kinematics.
Sports Biomech. 2008 May;7(2):160-72.
In this study, we compared sprint kinematics of sled towing and vest sprinting with the same relative loads. Twenty athletes performed 30-m sprints in three different conditions: (a) un-resisted, (b) sled towing, and (c) vest sprinting. During sled towing and vest sprinting, external loads of 15% and 20% of body mass were used. Sprint times were recorded over 10 and 30 m. Sagittal-plane high-speed video data were recorded at 5, 15, and 25 m from the start. Relative to the un-resisted condition, sprint time increased (7.5 to 19.8%) in both resisted conditions, resulting mainly from decreased step length (-5.2 to -16.5%) with small decreases in step frequency (-2.7 to -6.1%). Sled towing increased stance phase duration (14.7 to 26.0%), trunk angle (12.5 to 71.5%), and knee angle (10.3 to 22.7%), and decreased swing phase duration (-4.8 to -15.2%) relative to the un-resisted condition. Vest sprinting increased stance phase duration (12.8 to 24.5%) and decreased swing phase duration (-8.4 to -14.4%) and trunk angle (-1.7 to -13.0%). There were significant differences between the two resisted conditions in trunk, thigh, and knee angles. We conclude that sled towing and vest sprinting have different effects on some kinematics and hence change the overload experienced by muscle groups.
Effects of three types of resisted sprint training devices on the kinematics of sprinting at maximum velocity.
J Strength Cond Res. 2008 May;22(3):890-7.
Resisted sprint running is a common training method for improving sprint-specific strength. For maximum specificity of training, the athlete's movement patterns during the training exercise should closely resemble those used when performing the sport. The purpose of this study was to compare the kinematics of sprinting at maximum velocity to the kinematics of sprinting when using three of types of resisted sprint training devices (sled, parachute, and weight belt). Eleven men and 7 women participated in the study. Flying sprints greater than 30 m were recorded by video and digitized with the use of biomechanical analysis software. The test conditions were compared using a 2-way analysis of variance with a post-hoc Tukey test of honestly significant differences. We found that the 3 types of resisted sprint training devices are appropriate devices for training the maximum velocity phase in sprinting. These devices exerted a substantial overload on the athlete, as indicated by reductions in stride length and running velocity, but induced only minor changes in the athlete's running technique. When training with resisted sprint training devices, the coach should use a high resistance so that the athlete experiences a large training stimulus, but not so high that the device induces substantial changes in sprinting technique. We recommend using a video overlay system to visually compare the movement patterns of the athlete in unloaded sprinting to sprinting with the training device. In particular, the coach should look for changes in the athlete's forward lean and changes in the angles of the support leg during the ground contact phase of the stride.
The effects of resisted sled-pulling sprint training on acceleration and maximum speed performance.
J Sports Med Phys Fitness. 2007 Mar;47(1):133. No abstract available.
The effects of resisted sprint training on acceleration performance and kinematics in soccer, rugby union, and Australian football players.
J Strength Cond Res. 2007 Feb;21(1):77-85.
Acceleration is a significant feature of game-deciding situations in the various codes of football. However little is known about the acceleration characteristics of football players, the effects of acceleration training, or the effectiveness of different training modalities. This study examined the effects of resisted sprint (RS) training (weighted sled towing) on acceleration performance (0-15 m), leg power (countermovement jump [CMJ], 5-bound test [5BT], and 50-cm drop jump [50DJ]), gait (foot contact time, stride length, stride frequency, step length, and flight time), and joint (shoulder, elbow, hip, and knee) kinematics in men (N = 30) currently playing soccer, rugby union, or Australian football. Gait and kinematic measurements were derived from the first and second strides of an acceleration effort. Participants were randomly assigned to 1 of 3 treatment conditions: (a) 8-week sprint training of two 1-h sessions x wk(-1) plus RS training (RS group, n = 10), (b) 8-week nonresisted sprint training program of two 1-h sessions x wk(-1) (NRS group, n = 10), or (c) control (n = 10). The results indicated that an 8-week RS training program (a) significantly improves acceleration and leg power (CMJ and 5BT) performance but is no more effective than an 8-week NRS training program, (b) significantly improves reactive strength (50DJ), and (c) has minimal impact on gait and upper- and lower-body kinematics during acceleration performance compared to an 8-week NRS training program. These findings suggest that RS training will not adversely affect acceleration kinematics and gait. Although apparently no more effective than NRS training, this training modality provides an overload stimulus to acceleration mechanics and recruitment of the hip and knee extensors, resulting in greater application of horizontal power.
The effects of resisted sled-pulling sprint training on acceleration and maximum speed performance.
J Sports Med Phys Fitness. 2005 Sep;45(3):284-90.
AIM: The purpose of the present study was to examine the effects of resisted (RS) and un-resisted (US) sprint training programs on acceleration and maximum speed performance. METHODS: Twenty-two male students (age 20.1+/-1.9 y, height 1.78+/-7 cm, and weight 73+/-2 kg) completed RS (n=11) or US (n=11) sprint training programs. The RS group followed a sprint-training program with 5 kg sled pulling and the US group followed a similar sprint-training program without sled pulling. The training program consisted of 4x20 m and 4x50 m maximal runs, and was applied 3 times/week for 8 weeks. Before and after the training programs the subjects performed a 50 m run and the running velocity of 0-10 m, 10-20 m, 20-40 m and 40-50 m was measured. In addition, stride length and stride frequency were evaluated at the 3(rd) stride in acceleration phase and between 42-47 m in maximum speed phase. RESULTS: The RS improved running velocity in the run sections 0-10 m and 0-20 m, while in US group the running velocity in all run sections in acceleration phase remained unchanged. In contrast, RS training had no effect on running velocity in maximum speed phase, whereas US improved running velocity in 20-40 m, 40-50 m, and 20-50 m run sections. Stride rate increased only after RS in acceleration phase (+7.1%), whereas stride length increased only after US in maximum speed phase (+5.5%). CONCLUSION: Sprint training with 5 kg sled pulling for 8 weeks improves acceleration performance (0-20), while un-resisted sprint training improves performance in maximum speed phase (20-40) in non-elite athletes. It appears that each phase of sprint run demands a specific training approach.
Effects of resisted sled towing on sprint kinematics in field-sport athletes.
J Strength Cond Res. 2003 Nov;17(4):760-7.
Weighted sled towing is a common resisted sprint training technique even though relatively little is known about the effects that such practice has on sprint kinematics. The purpose of this study was to explore the effects of sled towing on acceleration sprint kinematics in field-sport athletes. Twenty men completed a series of sprints without resistance and with loads equating to 12.6 and 32.2% of body mass. Stride length was significantly reduced by approximately 10 and approximately 24% for each load, respectively. Stride frequency also decreased, but not to the extent of stride length. In addition, sled towing increased ground contact time, trunk lean, and hip flexion. Upper-body results showed an increase in shoulder range of motion with added resistance. The heavier load generally resulted in a greater disruption to normal acceleration kinematics compared with the lighter load. The lighter load is likely best for use in a training program.
Effect of elastic-cord towing on the kinematics of the acceleration phase of sprinting.
J Strength Cond Res. 2003 Feb;17(1):72-5.
We studied the specificity of elastic-cord towing by measuring selected kinematics of the acceleration phase of sprinting. Nine collegiate sprinters ran two 20-m maximal sprints (MSs) and towed sprints (TSs) that were recorded on high-speed video (180 Hz). Sagittal plane kinematics of a 4-segment model of the right side of the body were digitized for a complete stride at the 15-m point for the fastest trial. Significant differences were observed for horizontal velocity of the center of mass (CoM), stride length (SL), and horizontal distance from the CoM of the foot to the CoM of the body. There was no significant difference in stride rate between the MS and TS conditions. Omega-squared analysis showed that elastic-cord towing accounted for most of the variance in acute changes in horizontal velocity (73%), SL (68%), and horizontal position of the CoM at foot contact (64%). Elastic-cord tow training resulted in significant acute changes in sprint kinematics in the acceleration phase of an MS that do not appear to be sprint specific. More research is needed on the specificity of TS training and long-term effects on sprinting performance.
A comparison of resistance running, normal sprint running, and supramaximal running was performed. Nineteen young, generally well-trained subjects were divided into 3 training groups: resistance, normal, and supramaximal groups. Resistance and supramaximal training was done using a towing device, providing extra resistance or propulsion forces, resulting in running speed differences of about 3.3% (supramaximal) and 8.5% (resistance), compared to normal sprinting. The training period was 6 weeks, with 3 training sessions per week (5 sprint-runs over 22 m). Running times were measured using photocells, and average step length and cadence were recorded by digital video. A small (0.5%) but significant overall pre-post difference was found in running velocity, but the 3 groups changed differently over the running conditions. All individual subjects improved sprinting velocity most on the trained form, at 1-2%, and thus, the principle of velocity specificity in sprint training was supported. This indicates that to obtain short-distance sprinting improvement in a short period of time, one may prefer normal sprinting over other training forms.
ASSISTED AND RESISTED METHODS FOR SPEED DEVELOPMENT
Sports Biomech. 2008 May;7(2):160-72.
In this study, we compared sprint kinematics of sled towing and vest sprinting with the same relative loads. Twenty athletes performed 30-m sprints in three different conditions: (a) un-resisted, (b) sled towing, and (c) vest sprinting. During sled towing and vest sprinting, external loads of 15% and 20% of body mass were used. Sprint times were recorded over 10 and 30 m. Sagittal-plane high-speed video data were recorded at 5, 15, and 25 m from the start. Relative to the un-resisted condition, sprint time increased (7.5 to 19.8%) in both resisted conditions, resulting mainly from decreased step length (-5.2 to -16.5%) with small decreases in step frequency (-2.7 to -6.1%). Sled towing increased stance phase duration (14.7 to 26.0%), trunk angle (12.5 to 71.5%), and knee angle (10.3 to 22.7%), and decreased swing phase duration (-4.8 to -15.2%) relative to the un-resisted condition. Vest sprinting increased stance phase duration (12.8 to 24.5%) and decreased swing phase duration (-8.4 to -14.4%) and trunk angle (-1.7 to -13.0%). There were significant differences between the two resisted conditions in trunk, thigh, and knee angles. We conclude that sled towing and vest sprinting have different effects on some kinematics and hence change the overload experienced by muscle groups.
Effects of three types of resisted sprint training devices on the kinematics of sprinting at maximum velocity.
J Strength Cond Res. 2008 May;22(3):890-7.
Resisted sprint running is a common training method for improving sprint-specific strength. For maximum specificity of training, the athlete's movement patterns during the training exercise should closely resemble those used when performing the sport. The purpose of this study was to compare the kinematics of sprinting at maximum velocity to the kinematics of sprinting when using three of types of resisted sprint training devices (sled, parachute, and weight belt). Eleven men and 7 women participated in the study. Flying sprints greater than 30 m were recorded by video and digitized with the use of biomechanical analysis software. The test conditions were compared using a 2-way analysis of variance with a post-hoc Tukey test of honestly significant differences. We found that the 3 types of resisted sprint training devices are appropriate devices for training the maximum velocity phase in sprinting. These devices exerted a substantial overload on the athlete, as indicated by reductions in stride length and running velocity, but induced only minor changes in the athlete's running technique. When training with resisted sprint training devices, the coach should use a high resistance so that the athlete experiences a large training stimulus, but not so high that the device induces substantial changes in sprinting technique. We recommend using a video overlay system to visually compare the movement patterns of the athlete in unloaded sprinting to sprinting with the training device. In particular, the coach should look for changes in the athlete's forward lean and changes in the angles of the support leg during the ground contact phase of the stride.
The effects of resisted sled-pulling sprint training on acceleration and maximum speed performance.
J Sports Med Phys Fitness. 2007 Mar;47(1):133. No abstract available.
The effects of resisted sprint training on acceleration performance and kinematics in soccer, rugby union, and Australian football players.
J Strength Cond Res. 2007 Feb;21(1):77-85.
Acceleration is a significant feature of game-deciding situations in the various codes of football. However little is known about the acceleration characteristics of football players, the effects of acceleration training, or the effectiveness of different training modalities. This study examined the effects of resisted sprint (RS) training (weighted sled towing) on acceleration performance (0-15 m), leg power (countermovement jump [CMJ], 5-bound test [5BT], and 50-cm drop jump [50DJ]), gait (foot contact time, stride length, stride frequency, step length, and flight time), and joint (shoulder, elbow, hip, and knee) kinematics in men (N = 30) currently playing soccer, rugby union, or Australian football. Gait and kinematic measurements were derived from the first and second strides of an acceleration effort. Participants were randomly assigned to 1 of 3 treatment conditions: (a) 8-week sprint training of two 1-h sessions x wk(-1) plus RS training (RS group, n = 10), (b) 8-week nonresisted sprint training program of two 1-h sessions x wk(-1) (NRS group, n = 10), or (c) control (n = 10). The results indicated that an 8-week RS training program (a) significantly improves acceleration and leg power (CMJ and 5BT) performance but is no more effective than an 8-week NRS training program, (b) significantly improves reactive strength (50DJ), and (c) has minimal impact on gait and upper- and lower-body kinematics during acceleration performance compared to an 8-week NRS training program. These findings suggest that RS training will not adversely affect acceleration kinematics and gait. Although apparently no more effective than NRS training, this training modality provides an overload stimulus to acceleration mechanics and recruitment of the hip and knee extensors, resulting in greater application of horizontal power.
The effects of resisted sled-pulling sprint training on acceleration and maximum speed performance.
J Sports Med Phys Fitness. 2005 Sep;45(3):284-90.
AIM: The purpose of the present study was to examine the effects of resisted (RS) and un-resisted (US) sprint training programs on acceleration and maximum speed performance. METHODS: Twenty-two male students (age 20.1+/-1.9 y, height 1.78+/-7 cm, and weight 73+/-2 kg) completed RS (n=11) or US (n=11) sprint training programs. The RS group followed a sprint-training program with 5 kg sled pulling and the US group followed a similar sprint-training program without sled pulling. The training program consisted of 4x20 m and 4x50 m maximal runs, and was applied 3 times/week for 8 weeks. Before and after the training programs the subjects performed a 50 m run and the running velocity of 0-10 m, 10-20 m, 20-40 m and 40-50 m was measured. In addition, stride length and stride frequency were evaluated at the 3(rd) stride in acceleration phase and between 42-47 m in maximum speed phase. RESULTS: The RS improved running velocity in the run sections 0-10 m and 0-20 m, while in US group the running velocity in all run sections in acceleration phase remained unchanged. In contrast, RS training had no effect on running velocity in maximum speed phase, whereas US improved running velocity in 20-40 m, 40-50 m, and 20-50 m run sections. Stride rate increased only after RS in acceleration phase (+7.1%), whereas stride length increased only after US in maximum speed phase (+5.5%). CONCLUSION: Sprint training with 5 kg sled pulling for 8 weeks improves acceleration performance (0-20), while un-resisted sprint training improves performance in maximum speed phase (20-40) in non-elite athletes. It appears that each phase of sprint run demands a specific training approach.
Effects of resisted sled towing on sprint kinematics in field-sport athletes.
J Strength Cond Res. 2003 Nov;17(4):760-7.
Weighted sled towing is a common resisted sprint training technique even though relatively little is known about the effects that such practice has on sprint kinematics. The purpose of this study was to explore the effects of sled towing on acceleration sprint kinematics in field-sport athletes. Twenty men completed a series of sprints without resistance and with loads equating to 12.6 and 32.2% of body mass. Stride length was significantly reduced by approximately 10 and approximately 24% for each load, respectively. Stride frequency also decreased, but not to the extent of stride length. In addition, sled towing increased ground contact time, trunk lean, and hip flexion. Upper-body results showed an increase in shoulder range of motion with added resistance. The heavier load generally resulted in a greater disruption to normal acceleration kinematics compared with the lighter load. The lighter load is likely best for use in a training program.
Effect of elastic-cord towing on the kinematics of the acceleration phase of sprinting.
J Strength Cond Res. 2003 Feb;17(1):72-5.
We studied the specificity of elastic-cord towing by measuring selected kinematics of the acceleration phase of sprinting. Nine collegiate sprinters ran two 20-m maximal sprints (MSs) and towed sprints (TSs) that were recorded on high-speed video (180 Hz). Sagittal plane kinematics of a 4-segment model of the right side of the body were digitized for a complete stride at the 15-m point for the fastest trial. Significant differences were observed for horizontal velocity of the center of mass (CoM), stride length (SL), and horizontal distance from the CoM of the foot to the CoM of the body. There was no significant difference in stride rate between the MS and TS conditions. Omega-squared analysis showed that elastic-cord towing accounted for most of the variance in acute changes in horizontal velocity (73%), SL (68%), and horizontal position of the CoM at foot contact (64%). Elastic-cord tow training resulted in significant acute changes in sprint kinematics in the acceleration phase of an MS that do not appear to be sprint specific. More research is needed on the specificity of TS training and long-term effects on sprinting performance.
Velocity specificity in early-phase sprint training.
J Strength Cond Res. 2006 Nov;20(4):833-7.
ASSISTED AND RESISTED METHODS FOR SPEED DEVELOPMENT
PART II - RESISTED SPEED METHODS
By Adrian Faccioni
RESISTANCE TRAINING
Any athlete wishing to increase running velocity must overcome the inertia of the body through the acceleration phase. In this phase, it is the strong extensors of the hip (gluteals and hamstrings), knee (quadriceps) and ankle (Gastrocnemius and Soleus) that are actively involved in the process (Chu & Korchemny 1989).
By Adrian Faccioni
RESISTANCE TRAINING
Any athlete wishing to increase running velocity must overcome the inertia of the body through the acceleration phase. In this phase, it is the strong extensors of the hip (gluteals and hamstrings), knee (quadriceps) and ankle (Gastrocnemius and Soleus) that are actively involved in the process (Chu & Korchemny 1989).
Mann & Sprague (1980), Mann (1981), Chapman & Caldwell (1983) and Chapmanet al (1984) all performed kinetic analyses on sprint performers and all concluded that the hip extensors produced the greatest muscle moments when analyzing hip, knee and ankle joint moments. (A muscle moment indicates the resultant muscle activity and details which muscle groups are dominating the activity). Therefore, to maximize horizontal velocity in both the acceleration and top running velocity phases, it is the hip extensor muscle groups that resistance training must target to increase their force output.
A second component of sprinting performance that can be targeted with resistance training is the minimizing of the drop of centre of gravity with each ground contact. The centre of gravity should not sink too low through the ground contact phase. The stronger the extensor muscle groups in the lower limb, the less drop in centre of gravity during the ground contact phase (Chu & Korchemny 1989). The less flexion of these joints, the greater the stretch reflex that will be activated, resulting in greater concentric contraction during the driving phase of each stride (Asmussen & Bond-Peterson 1974, Cavagna 1977).
The components of strength required for maximizing sprint performance are maximum -strength, and speed-strength components, explosive-strength, and reactive-strength (stretch-shortening cycle). It has been well documented that one of the best methods to increase maximal-strength is through low-repetition (1 to 10) and high-intensity (70 to 120%) weight training. (Berger, 1962a, b, Atha1981, Anderson & Kearney, 1982, Schmidtbleicher 1985).
It is from a sound strength base that the speed-strength components explosive- and reactive -strength can be developed through movement-specific training regimes using a variety of different methods. Each method is designed to increase the stress placed upon the major extensor muscle groups. The increased force production by these muscle groups is then transferred to greater stride length which, when combined with an optimal stride rate, will lead to an increase in horizontal velocity (m/s).
WEIGHTED VEST RUNNING
A study by Bosco et al (1986) looked at the effect of increasing body weight (7 to 8%) on sprint athletes over a three-week period, training 3 to 5 sessions per week. The added resistance through weighted vests was worn from morning to evening and the athletes were tested for jumping and running on a treadmill, pre and post experiment. The jump tests included squat jumps (SJ), counter-movement jump, drop jump and 15 seconds continuous jumps on a resistive platform. The SJ improved from 42.9cm to 47.4cm and as the correlation between maximal running velocity and SJ has been measured at 0.68 (Mero et al 1981), the increased loading would have a positive effect upon force production and running speed.
Another positive effect of weight vest running is that the added mass would increase the vertical force at each ground contact. This would increase the stress placed on the stretch-shortening cycle (reactive strength) function of the muscle and would improve muscle stiffness at ground contact (Komi 1986). This would improve the muscle’s capacity to tolerate greater stretch loads, store more elastic energy and improve power output, which may be seen in an increase in stride length. Whilst this study suggested the wearing of a weighted vest all day, it was only a three-week project, and over a longer period it could be assumed that loading only during training sessions would have a similar effect.
UPHILL RUNNING
Kunz & Kaufmann (1981) completed a biomechanical study on maximal running up a 3% incline. They found the velocity to be slower than that of level ground running (8.35m/s to 8.85m/s) and biomechanically the subjects performed the runs with shorter stride lengths and longer ground contact times. The authors feel that uphill running will increase the stress placed on the hip extensor muscle groups as the athlete will attempt to maximize stride length, therefore increasing this component on the flat surface.
They also feel this training method will develop a shorter ground contact time if the athlete emphasizes fast push off to conquer the effects of the positive grade. An incline of greater than 3% would still be beneficial in developing the forceful hip extensor movements required but will be less specific in the simulation of the specific technical movements of the sprint
action.
SAND AND WATER RUNNING
Whilst both environments are ideal to increase the resistance placed upon a running athlete, they both have limited application to increasing stride length (utilization of hip extensors). The resistance in running in these two conditions leads to a greater activation of the hip flexors rather than the hip extensors. In shallow water running (20 to 30cm), the main emphasis is to get the leg out of the water. When running in soft sand, the ability to apply great extension force is diminished and the increase in speed is through an increase in stride rate through a shorter stride and faster hip flexion activity.
TOWING (RESISTED)
Towing either a sled, tire, speed chute or other weighted device over set distances are frequently used methods to develop running speed. The basis behind these methods is to increase the movement resistance requiring the athlete to increase force output (especially in the hip, knee and ankle extensors) to continue to run at speed. Studies by Behm (1991), Hakkinen et al (1985), Komi et al (1982) and Hakkinen & Komi (1985) all suggest that the improvement of a particular action (e.g. sprinting speed) is directly related to the similarity of movement in the training regime and the velocity specificity of the movement.
The two major towing methods used in Australia are that of tire or sled towing and the use of the speed chute (Speed Chute Australia). The benefits of using a tire or sled are that it is quite easy to change the size of the tire from small to large (thereby increasing the resistance), or using a tire with weights placed inside to increase resistance. A sled can be easily designed that allows weights to be secured, again making the resistance greater. It is important to have a long attachment to the towed device (10m), as shorter attachments can restrict the flat sliding of the device, leading to bouncing of the tire or sled as the athlete increases speed.
The second method, that of speed chute towing requires the use of a combination of small parachutes depending on the amount of resistance needed. Advantages of this device is that it is easily transported and the chute size can be changed very quickly. The chutes can be easily released mid-flight, allowing the athlete to finish a repetition with no increased resistance, giving the athlete the sensation of increased speed. A major disadvantage is that the chutes do not stay directly behind the athlete during the repetition. They move about from side to side (even more so in windy conditions) and can make it very difficult for the athlete to run at any great speed as he/she is trying to keep balance throughout each repetition. This may be of some use to team sport athletes, who are attempting to sprint whilst having to dodge and weave between opposing players, but for the purpose of purely increasing running speed, they have limited application.
SPEED-STRENGTH JUMPS (PLYOMETRICS)
Behm (1991), Hakkinen etal(1985), Komi et al (1982) and Hakkinen & Komi (1985) Smith & Melton (1981), Caiozzo et al (1981), Coyle et al (1981), and Kanehisa & Miyashita (1983a, b) all detailed research showing that high velocity, light resistance training led to a speed-specific enhancement of the neuromuscular system. This enhancement increased the subjects’ abilities to move small resistances with speed (such as own body weight) as shown by performance levels in the high velocity portion of a force- velocity curve.
These researchers measured squat jumps, counter-movement jumps, standing long jump, and isometric rate of force production with results indicating that adaptation was different to that achieved from heavy force to the ground, therefore requiring an increase in the early portion of the force production curve (increased rate of force production). The training modality can include long alternate leg bounds, double and single leg hops, hurdle jumps, and sandpit jumps. The movements can be dynamic in nature depending on the phase of training (Preparation phase — less intensity, Competition phase — more intensity, less volume).
WEIGHTED VEST RUNNING
A study by Bosco et al (1986) looked at the effect of increasing body weight (7 to 8%) on sprint athletes over a three-week period, training 3 to 5 sessions per week. The added resistance through weighted vests was worn from morning to evening and the athletes were tested for jumping and running on a treadmill, pre and post experiment. The jump tests included squat jumps (SJ), counter-movement jump, drop jump and 15 seconds continuous jumps on a resistive platform. The SJ improved from 42.9cm to 47.4cm and as the correlation between maximal running velocity and SJ has been measured at 0.68 (Mero et al 1981), the increased loading would have a positive effect upon force production and running speed.
Another positive effect of weight vest running is that the added mass would increase the vertical force at each ground contact. This would increase the stress placed on the stretch-shortening cycle (reactive strength) function of the muscle and would improve muscle stiffness at ground contact (Komi 1986). This would improve the muscle’s capacity to tolerate greater stretch loads, store more elastic energy and improve power output, which may be seen in an increase in stride length. Whilst this study suggested the wearing of a weighted vest all day, it was only a three-week project, and over a longer period it could be assumed that loading only during training sessions would have a similar effect.
UPHILL RUNNING
Kunz & Kaufmann (1981) completed a biomechanical study on maximal running up a 3% incline. They found the velocity to be slower than that of level ground running (8.35m/s to 8.85m/s) and biomechanically the subjects performed the runs with shorter stride lengths and longer ground contact times. The authors feel that uphill running will increase the stress placed on the hip extensor muscle groups as the athlete will attempt to maximize stride length, therefore increasing this component on the flat surface.
They also feel this training method will develop a shorter ground contact time if the athlete emphasizes fast push off to conquer the effects of the positive grade. An incline of greater than 3% would still be beneficial in developing the forceful hip extensor movements required but will be less specific in the simulation of the specific technical movements of the sprint
action.
SAND AND WATER RUNNING
Whilst both environments are ideal to increase the resistance placed upon a running athlete, they both have limited application to increasing stride length (utilization of hip extensors). The resistance in running in these two conditions leads to a greater activation of the hip flexors rather than the hip extensors. In shallow water running (20 to 30cm), the main emphasis is to get the leg out of the water. When running in soft sand, the ability to apply great extension force is diminished and the increase in speed is through an increase in stride rate through a shorter stride and faster hip flexion activity.
TOWING (RESISTED)
Towing either a sled, tire, speed chute or other weighted device over set distances are frequently used methods to develop running speed. The basis behind these methods is to increase the movement resistance requiring the athlete to increase force output (especially in the hip, knee and ankle extensors) to continue to run at speed. Studies by Behm (1991), Hakkinen et al (1985), Komi et al (1982) and Hakkinen & Komi (1985) all suggest that the improvement of a particular action (e.g. sprinting speed) is directly related to the similarity of movement in the training regime and the velocity specificity of the movement.
The two major towing methods used in Australia are that of tire or sled towing and the use of the speed chute (Speed Chute Australia). The benefits of using a tire or sled are that it is quite easy to change the size of the tire from small to large (thereby increasing the resistance), or using a tire with weights placed inside to increase resistance. A sled can be easily designed that allows weights to be secured, again making the resistance greater. It is important to have a long attachment to the towed device (10m), as shorter attachments can restrict the flat sliding of the device, leading to bouncing of the tire or sled as the athlete increases speed.
The second method, that of speed chute towing requires the use of a combination of small parachutes depending on the amount of resistance needed. Advantages of this device is that it is easily transported and the chute size can be changed very quickly. The chutes can be easily released mid-flight, allowing the athlete to finish a repetition with no increased resistance, giving the athlete the sensation of increased speed. A major disadvantage is that the chutes do not stay directly behind the athlete during the repetition. They move about from side to side (even more so in windy conditions) and can make it very difficult for the athlete to run at any great speed as he/she is trying to keep balance throughout each repetition. This may be of some use to team sport athletes, who are attempting to sprint whilst having to dodge and weave between opposing players, but for the purpose of purely increasing running speed, they have limited application.
SPEED-STRENGTH JUMPS (PLYOMETRICS)
Behm (1991), Hakkinen etal(1985), Komi et al (1982) and Hakkinen & Komi (1985) Smith & Melton (1981), Caiozzo et al (1981), Coyle et al (1981), and Kanehisa & Miyashita (1983a, b) all detailed research showing that high velocity, light resistance training led to a speed-specific enhancement of the neuromuscular system. This enhancement increased the subjects’ abilities to move small resistances with speed (such as own body weight) as shown by performance levels in the high velocity portion of a force- velocity curve.
These researchers measured squat jumps, counter-movement jumps, standing long jump, and isometric rate of force production with results indicating that adaptation was different to that achieved from heavy force to the ground, therefore requiring an increase in the early portion of the force production curve (increased rate of force production). The training modality can include long alternate leg bounds, double and single leg hops, hurdle jumps, and sandpit jumps. The movements can be dynamic in nature depending on the phase of training (Preparation phase — less intensity, Competition phase — more intensity, less volume).
Monday, June 30, 2008
Repeated Sprint Ability
Effect of recovery mode on repeated sprint ability in young basketball players.
J Strength Cond Res. 2008 May;22(3):923-9.
The aim of this study was to examine the effect of recovery mode on repeated sprint ability in young basketball players. Sixteen basketball players (age, 16.8 +/- 1.2 years; height, 181.3 +/- 5.7 cm; body mass, 73 +/- 10 kg; VO2max, 59.5 +/- 7.9 mL x kg(-1) x min(-1)) performed in random order over 2 separate occasions 2 repeated sprint ability protocols consisting of 10 x 30-m shuttle run sprints with 30 seconds of passive or active (running at 50% of maximal aerobic speed) recovery. Results showed that fatigue index (FI) during the active protocol was significantly greater than in the passive condition (5.05 +/- 2.4, and 3.39 +/- 2.3, respectively, p < 0.001). No significant association was found between VO2peak and FI and sprint total time (TT) in either repeated sprint protocols. Blood lactate concentration at 3 minutes post exercise was not significantly different between the 2 recovery conditions. The results of this study show that during repeated sprinting, passive recovery enabled better performance, reducing fatigue. Consequently, the use of passive recovery is advisable during competition in order to limit fatigue as a consequence of repeated high intensity exercise.
Relationship between measured maximal oxygen uptake and aerobic endurance performance with running repeated sprint ability in young elite soccer players.
J Sports Med Phys Fitness. 2007 Dec;47(4):401-7.
AIM: The aim of the study was to determine the relationships between maximal oxygen uptake (VO(2max)) in a maximal treadmill run and the aerobic endurance performance in the 20-m multistage shuttle run (MST) test, with the performance indices obtained in the running repeated sprint ability (rRSA) test, in elite youth soccer players. METHODS: Thirty-seven adolescent male outfield players performed on separate days and in random order the treadmill run test and the MST, to obtain their measured VO(2max) and aerobic endurance performance (via the number of completed shuttles in the MST), respectively. Players also completed the rRSA test of 6x20-m all-out sprints, interspersed with 20 s of active recovery. RESULTS: There was a significant moderate correlation between measured VO(2max) (in L . min(-1) and mL . kg(-1) . min(-1)) and MST results (r=0.43 and 0.54, P<0.05, respectively). There was no significant correlation between measured VO(2max) and aerobic endurance performance with any of the performance indices in the rRSA test (all P>0.05). CONCLUSION: The moderate association between the measured VO(2max) and MST suggests that both tests were plausibly measuring different aspects of a player's aerobic fitness. The lack of association between measured VO(2max) and aerobic endurance performance in the MST with performance in the rRSA suggests that aerobic fitness per se is poorly associated with performance in the rRSA in elite youth soccer players.
Sprint vs. Interval Training in Football.
Int J Sports Med. 2007 Dec 17. [Epub ahead of print]
The aim of this study was to compare the effects of high-intensity aerobic interval and repeated-sprint ability (RSA) training on aerobic and anaerobic physiological variables in male football players. Forty-two participants were randomly assigned to either the interval training group (ITG, 4 x 4 min running at 90 - 95 % of HR (max); n = 21) or repeated-sprint training group (RSG, 3 x 6 maximal shuttle sprints of 40 m; n = 21). The following outcomes were measured at baseline and after 7 weeks of training: maximum oxygen uptake, respiratory compensation point, football-specific endurance (Yo-Yo Intermittent Recovery Test, YYIRT), 10-m sprint time, jump height and power, and RSA. Significant group x time interaction was found for YYIRT (p = 0.003) with RSG showing greater improvement (from 1917 +/- 439 to 2455 +/- 488 m) than ITG (from 1846 +/- 329 to 2077 +/- 300 m). Similarly, a significant interaction was found in RSA mean time (p = 0.006) with only the RSG group showing an improvement after training (from 7.53 +/- 0.21 to 7.37 +/- 0.17 s). No other group x time interactions were found. Significant pre-post changes were found for absolute and relative maximum oxygen uptake and respiratory compensation point (p < 0.05). These findings suggest that the RSA training protocol used in this study can be an effective training strategy for inducing aerobic and football-specific training adaptations.
J Strength Cond Res. 2008 May;22(3):923-9.
The aim of this study was to examine the effect of recovery mode on repeated sprint ability in young basketball players. Sixteen basketball players (age, 16.8 +/- 1.2 years; height, 181.3 +/- 5.7 cm; body mass, 73 +/- 10 kg; VO2max, 59.5 +/- 7.9 mL x kg(-1) x min(-1)) performed in random order over 2 separate occasions 2 repeated sprint ability protocols consisting of 10 x 30-m shuttle run sprints with 30 seconds of passive or active (running at 50% of maximal aerobic speed) recovery. Results showed that fatigue index (FI) during the active protocol was significantly greater than in the passive condition (5.05 +/- 2.4, and 3.39 +/- 2.3, respectively, p < 0.001). No significant association was found between VO2peak and FI and sprint total time (TT) in either repeated sprint protocols. Blood lactate concentration at 3 minutes post exercise was not significantly different between the 2 recovery conditions. The results of this study show that during repeated sprinting, passive recovery enabled better performance, reducing fatigue. Consequently, the use of passive recovery is advisable during competition in order to limit fatigue as a consequence of repeated high intensity exercise.
Relationship between measured maximal oxygen uptake and aerobic endurance performance with running repeated sprint ability in young elite soccer players.
J Sports Med Phys Fitness. 2007 Dec;47(4):401-7.
AIM: The aim of the study was to determine the relationships between maximal oxygen uptake (VO(2max)) in a maximal treadmill run and the aerobic endurance performance in the 20-m multistage shuttle run (MST) test, with the performance indices obtained in the running repeated sprint ability (rRSA) test, in elite youth soccer players. METHODS: Thirty-seven adolescent male outfield players performed on separate days and in random order the treadmill run test and the MST, to obtain their measured VO(2max) and aerobic endurance performance (via the number of completed shuttles in the MST), respectively. Players also completed the rRSA test of 6x20-m all-out sprints, interspersed with 20 s of active recovery. RESULTS: There was a significant moderate correlation between measured VO(2max) (in L . min(-1) and mL . kg(-1) . min(-1)) and MST results (r=0.43 and 0.54, P<0.05, respectively). There was no significant correlation between measured VO(2max) and aerobic endurance performance with any of the performance indices in the rRSA test (all P>0.05). CONCLUSION: The moderate association between the measured VO(2max) and MST suggests that both tests were plausibly measuring different aspects of a player's aerobic fitness. The lack of association between measured VO(2max) and aerobic endurance performance in the MST with performance in the rRSA suggests that aerobic fitness per se is poorly associated with performance in the rRSA in elite youth soccer players.
Sprint vs. Interval Training in Football.
Int J Sports Med. 2007 Dec 17. [Epub ahead of print]
The aim of this study was to compare the effects of high-intensity aerobic interval and repeated-sprint ability (RSA) training on aerobic and anaerobic physiological variables in male football players. Forty-two participants were randomly assigned to either the interval training group (ITG, 4 x 4 min running at 90 - 95 % of HR (max); n = 21) or repeated-sprint training group (RSG, 3 x 6 maximal shuttle sprints of 40 m; n = 21). The following outcomes were measured at baseline and after 7 weeks of training: maximum oxygen uptake, respiratory compensation point, football-specific endurance (Yo-Yo Intermittent Recovery Test, YYIRT), 10-m sprint time, jump height and power, and RSA. Significant group x time interaction was found for YYIRT (p = 0.003) with RSG showing greater improvement (from 1917 +/- 439 to 2455 +/- 488 m) than ITG (from 1846 +/- 329 to 2077 +/- 300 m). Similarly, a significant interaction was found in RSA mean time (p = 0.006) with only the RSG group showing an improvement after training (from 7.53 +/- 0.21 to 7.37 +/- 0.17 s). No other group x time interactions were found. Significant pre-post changes were found for absolute and relative maximum oxygen uptake and respiratory compensation point (p < 0.05). These findings suggest that the RSA training protocol used in this study can be an effective training strategy for inducing aerobic and football-specific training adaptations.
Sprinting
The use of various strength-power tests as predictors of sprint running performance.
J Sports Med Phys Fitness. 2008 Mar;48(1):49-54.
The present findings suggest that the ability to produce force quickly, as measured by the time to achieve 60% of maximum voluntary contraction is related to sprinting performance, with the coefficient of determination accounting for 53% of the variance in the data. These data also show that sprinting ability is linked with DJ performance, especially the drop jump from a height of 30 cm (11.8 in).
Effects of sprint and plyometric training on muscle function and athletic performance.
J Strength Cond Res. 2007 May;21(2):543-9.
We conclude that short-term sprint training produces similar or even greater training effects in muscle function and athletic performance than does conventional plyometric training. This study provides support for the use of sprint training as an applicable training method of improving explosive performance of athletes in general.
The relationship between maximal jump-squat power and sprint acceleration in athletes.
Eur J Appl Physiol. 2004 Jan;91(1):46-52.
Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.
Relationship between strength qualities and sprinting performance.
J Sports Med Phys Fitness. 1995 Mar;35(1):13-9.
The single best correlate of maximum sprinting speed was the force applied at 100 ms (relative to bodyweight) from the start of a loaded jumping action (concentric contraction) (r = 0.80, p = 0.0001). SSC measures and maximum absolute strength were more related to maximum sprinting speed than starting ability. It was concluded that strength qualities were related to sprinting performance and these relationships differed for starting and maximum speed sprinting.
The contribution of maximal force production to explosive movement among young collegiate athletes.
J Strength Cond Res. 2006 Nov;20(4):867-73.
Muscular strength, peak power output, vertical jumping ability, standing broad jump, agility, sprint acceleration, and sprint velocity were all shown to be very highly related. Further examination demonstrated that body mass-adjusted muscular strength is more highly related to performance measures than is absolute muscular strength.
A comparison of drop jump training methods: effects on leg extensor strength qualities and jumping performance.
Int J Sports Med. 1999 Jul;20(5):295-303.
It was concluded that DJ-H/t method was effective for the development of RS, but training with DJ-H was not intense and/or specific enough to stimulate gains in strength qualities of the leg extensors or jumping performance.
- key words: sprint running -
Effects of sprint and plyometric training on muscle function and athletic performance.
J Strength Cond Res. 2007 May;21(2):543-9.
We conclude that short-term sprint training produces similar or even greater training effects in muscle function and athletic performance than does conventional plyometric training. This study provides support for the use of sprint training as an applicable training method of improving explosive performance of athletes in general.
Aging, muscle fiber type, and contractile function in sprint-trained athletes.
J Appl Physiol. 2006 Sep;101(3):906-17. Epub 2006 May 11.
The sprint-trained athletes experienced the typical aging-related reduction in the size of fast fibers, a shift toward a slower MHC isoform profile, and a lower V(o) of type I MHC fibers, which played a role in the decline in explosive force production. However, the muscle characteristics were preserved at a high level in the oldest runners, underlining the favorable impact of sprint exercise on aging muscle.
Effects of hip flexor training on sprint, shuttle run, and vertical jump performance.
J Strength Cond Res. 2005 Aug;19(3):615-21.
Individuals in the training group improved hip flexion strength by 12.2% and decreased their 40-yd and shuttle run times by 3.8% and 9.0%, respectively. An increase in hip flexion strength can help to improve sprint and agility performance for physically active, untrained individuals.
Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players.
Br J Sports Med. 2004 Jun;38(3):285-8.
Maximal strength in half squats determines sprint performance and jumping height in high level soccer players. High squat strength did not imply reduced maximal oxygen consumption. Elite soccer players should focus on maximal strength training, with emphasis on maximal mobilisation of concentric movements, which may improve their sprinting and jumping performance.
Which starting style is faster in sprint running - standing or crouch start?
Sports Biomech. 2004 Jan;3(1):43-53.
Six university track team sprinters performed 2 x 3 x 50 m trials...during the first steps of the performance the standing start produced higher body centre of mass horizontal velocity than the crouch start. This may be due to the longer distance between the feet in the standing start, which caused longer push-off phases, and the work against gravity in the crouch start. However, this advantage in horizontal velocity disappeared by the 10 m mark, where similar velocities were recorded with both start styles. Further, there was no statistically significant difference between the two starting styles in horizontal velocity at the 25 m mark, nor in the time to reach the 25 m or 50 m mark.
Interaction of step length and step rate during sprint running.
Med Sci Sports Exerc. 2004 Feb;36(2):261-71.
A "negative interaction" between step length and step rate refers to an increase in one factor resulting in a decrease in the other...A wide range of step length and step rate combinations was evident, even for subgroups of athletes with similar sprint velocities. This was partly due to a negative interaction that existed between step length and step rate; that is, those athletes who used a longer step length tended to have a lower step rate and vice versa. Vertical velocity of takeoff was the most prominent source of the negative interaction.
The relationship between maximal jump-squat power and sprint acceleration in athletes.
Eur J Appl Physiol. 2004 Jan;91(1):46-52. Epub 2003 Sep 24.
This study investigated the relationship between sprint start performance (5-m time) and strength and power variables. Thirty male athletes [height: 183.8 (6.8) cm, and mass: 90.6 (9.3) kg; mean (SD)] each completed six 10-m sprints from a standing start...Three to six days later subjects completed three concentric jump squats, using a traditional and split technique, at a range of external loads from 30-70% of one repetition maximum (1RM)...Average and peak power were similar during the split squat and the traditional squat and both were significantly related to 5-m time ( r=-0.64 to -0.68, P<0.001)...Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.
Age-related differences in 100-m sprint performance in male and female master runners.
Med Sci Sports Exerc. 2003 Aug;35(8):1419-28.
There was a general decline in sprint performances with age, the decrease becoming more evident around 65-70 yr of age. The velocity during the different phases of the run declined on average from 5 to 6% per decade in males and from 5 to 7% per decade in females. Similarly, SL showed clear reductions with increasing age, whereas SR remained unchanged until the oldest age groups in both genders. Furthermore, the CT, which correlated with velocity, was significantly longer, and FT, which correlated with both velocity and SL, was shorter in older age groups. CONCLUSION: Our findings indicated that age-associated differences in velocity in elite master sprinters were similar in each phase of the 100-m run. The deterioration of the overall performance with age was primarily related to reduction in SL and increase in CT.
Effect of the movement speed of resistance training exercises on sprint and strength performance in concurrently training elite junior sprinters.
J Sports Sci. 2002 Dec;20(12):981-90.
The aim of this study was to determine the effects of 7 weeks of high- and low-velocity resistance training on strength and sprint running performance in nine male elite junior sprint runners (age 19.0+/-1.4 years, best 100 m times 10.89+/-0.21 s; mean +/- s). The athletes continued their sprint training throughout the study, but their resistance training programme was replaced by one in which the movement velocities of hip extension and flexion, knee extension and flexion and squat exercises varied according to the loads lifted (i.e. 30-50% and 70-90% of 1-RM in the high- and low-velocity training groups, respectively). There were no between-group differences in hip flexion or extension torque produced at 1.05, 4.74 or 8.42 rad x s(-1), 20 m acceleration or 20 m 'flying' running times, or 1-RM squat lift strength either before or after training. This was despite significant improvements in 20 m acceleration time (P < 0.01), squat strength (P < 0.05), isokinetic hip flexion torque at 4.74 rad x s(-1) and hip extension torque at 1.05 and 4.74 rad x s(-1) for the athletes as a whole over the training period. Although velocity-specific strength adaptations have been shown to occur rapidly in untrained and nonconcurrently training individuals, the present results suggest a lack of velocity-specific performance changes in elite concurrently training sprint runners performing a combination of traditional and semi-specific resistance training exercises.
Leg strength and stiffness as ability factors in 100 m sprint running.
J Sports Med Phys Fitness. 2002 Sep;42(3):274-81.
BACKGROUND: The purpose of this study was to determine the importance of leg strength and stiffness relative to i) 100 m sprint performance, ii) mean speed on the three phases of the 100 m race (30-60-100 m) and iii) the speed differences between these phases. METHODS: Nineteen regional to national level male sprinters competed in a 100 m race. Video analysis was used to determine mean velocity parameters. Two subgroups were created since some of the runners decreased their velocity during the third phase (G1), whereas others maintained or accelerated it (G2). Leg strength (concentric half-squats - counter movement jump) and stiffness (hopping) were determined. RESULTS: The mean performance over 100 m was 11.43 sec (10.72-12.87 sec). The concentric half-squats were related to 100 m (r=0.74, p<0.001) and to the mean speed of each phase (R=0.75, p<0.01). The counter movement jump was related to 100 m (r=0.57, p<0.05) and was the predictor of the first phase (r=0.66, p<0.01). The hopping test was the predictor of the two last phases (R=0.66, p<0.05). Athletes who had the greatest leg stiffness (G1) produced the highest acceleration between the first and the second phases, and presented a deceleration between the second and the third ones.
Long-term metabolic and skeletal muscle adaptations to short-sprint training: implications for sprint training and tapering.
Sports Med. 2001;31(15):1063-82. Review.
The adaptations of muscle to sprint training can be separated into metabolic and morphological changes. Enzyme adaptations represent a major metabolic adaptation to sprint training, with the enzymes of all three energy systems showing signs of adaptation to training and some evidence of a return to baseline levels with detraining. Myokinase and creatine phosphokinase have shown small increases as a result of short-sprint training in some studies and elite sprinters appear better able to rapidly breakdown phosphocreatine (PCr) than the sub-elite. No changes in these enzyme levels have been reported as a result of detraining. Similarly, glycolytic enzyme activity (notably lactate dehydrogenase, phosphofructokinase and glycogen phosphorylase) has been shown to increase after training consisting of either long (>10-second) or short (<10-second) sprints. Evidence suggests that these enzymes return to pre-training levels after somewhere between 7 weeks and 6 months of detraining. Mitochondrial enzyme activity also increases after sprint training, particularly when long sprints or short recovery between short sprints are used as the training stimulus. Morphological adaptations to sprint training include changes in muscle fibre type, sarcoplasmic reticulum, and fibre cross-sectional area. An appropriate sprint training programme could be expected to induce a shift toward type IIa muscle, increase muscle cross-sectional area and increase the sarcoplasmic reticulum volume to aid release of Ca(2+). Training volume and/or frequency of sprint training in excess of what is optimal for an individual, however, will induce a shift toward slower muscle contractile characteristics. In contrast, detraining appears to shift the contractile characteristics towards type IIb, although muscle atrophy is also likely to occur. Muscle conduction velocity appears to be a potential non-invasive method of monitoring contractile changes in response to sprint training and detraining. In summary, adaptation to sprint training is clearly dependent on the duration of sprinting, recovery between repetitions, total volume and frequency of training bouts. These variables have profound effects on the metabolic, structural and performance adaptations from a sprint-training programme and these changes take a considerable period of time to return to baseline after a period of detraining. However, the complexity of the interaction between the aforementioned variables and training adaptation combined with individual differences is clearly disruptive to the transfer of knowledge and advice from laboratory to coach to athlete.
Relationship of the stretch-shortening cycle to sprint performance in trained female athletes.
J Strength Cond Res. 2001 Aug;15(3):326-31.
Seventeen trained, female, high school, competitive sprinters completed the following tests: countermovement jump for vertical distance (CMJ), bounce drop jump for height with minimum ground contact time (BDJ index), and ground contact time (GCT) during the BDJ and a 5-step bound (5B) test...Sprint performances at 30-, 100-, and 300-m distances were assessed...Significant correlations (p < 0.05) existed between CMJ and 30-m (r = -0.60), 100-m (r = -0.64), and 300-m (r = -0.55) sprint times; BDJ index and 30-m (r = -0.79) and 100-m (r = -0.75) sprint times; and 5B test and 300-m sprint time (r = -0.54)...Results indicated that the BDJ index and CMJ tests were significantly related to sprint performances in female athletes.
Neural influences on sprint running: training adaptations and acute responses.
Sports Med. 2001;31(6):409-25. Review.
Performance in sprint exercise is determined by the ability to accelerate, the magnitude of maximal velocity and the ability to maintain velocity against the onset of fatigue. These factors are strongly influenced by metabolic and anthropometric components. Improved temporal sequencing of muscle activation and/or improved fast twitch fibre recruitment may contribute to superior sprint performance. Speed of impulse transmission along the motor axon may also have implications on sprint performance. Nerve conduction velocity (NCV) has been shown to increase in response to a period of sprint training. However, it is difficult to determine if increased NCV is likely to contribute to improved sprint performance. An increase in motoneuron excitability, as measured by the Hoffman reflex (H-reflex), has been reported to produce a more powerful muscular contraction, hence maximising motoneuron excitability would be expected to benefit sprint performance. Motoneuron excitability can be raised acutely by an appropriate stimulus with obvious implications for sprint performance. However, at rest H-reflex has been reported to be lower in athletes trained for explosive events compared with endurance-trained athletes. This may be caused by the relatively high, fast twitch fibre percentage and the consequent high activation thresholds of such motor units in power-trained populations. In contrast, stretch reflexes appear to be enhanced in sprint athletes possibly because of increased muscle spindle sensitivity as a result of sprint training. With muscle in a contracted state, however, there is evidence to suggest greater reflex potentiation among both sprint and resistance-trained populations compared with controls. Again this may be indicative of the predominant types of motor units in these populations, but may also mean an enhanced reflex contribution to force production during running in sprint-trained athletes. Fatigue of neural origin both during and following sprint exercise has implications with respect to optimising training frequency and volume. Research suggests athletes are unable to maintain maximal firing frequencies for the full duration of, for example, a 100m sprint. Fatigue after a single training session may also have a neural manifestation with some athletes unable to voluntarily fully activate muscle or experiencing stretch reflex inhibition after heavy training. This may occur in conjunction with muscle damage. Research investigating the neural influences on sprint performance is limited. Further longitudinal research is necessary to improve our understanding of neural factors that contribute to training-induced improvements in sprint performance.
Muscle power patterns in the mid-acceleration phase of sprinting.
J Sports Sci. 2001 Apr;19(4):263-72.
To assess the role of the lower limb joints in generating velocity in the mid-acceleration phase of sprinting, muscle power patterns of the hip, knee and ankle were determined. Six male sprinters with a mean 100 m time of 10.75 s performed repeated maximal sprints along a 35 m indoor track. A complete stride across a force platform, positioned at approximately 14 m into the sprint, was video-recorded for analysis. Smoothed coordinate data were obtained from manual digitization of (50 Hz) video images and were then interpolated to match the sampling rate of the recorded ground reaction force (1000 Hz). The moment at each joint was then calculated using inverse dynamics and multiplied by the angular velocity to determine the muscle power. The results showed a proximal-to-distal timing in the generation of peak extensor power during stance at the hip, the knee and then the ankle, with the plantar flexors producing the greatest peak power. Apart from a moderate power generation peak towards toe-off, knee power was negligible despite a large extensor moment throughout stance. The role of the knee thus appears to be one of maintaining the centre of mass height and enabling the power generated at the hip to be transferred to the ankle.
Leg power and hopping stiffness: relationship with sprint running performance.
Med Sci Sports Exerc. 2001 Feb;33(2):326-33.
PURPOSE: Although sprint performance undoubtedly involves muscle power, the stiffness of the leg also determines sprint performance while running at maximal velocity. Results that include both of these characteristics have not been directly obtained in previous studies on human runners. We have therefore studied the link between leg power, leg stiffness, and sprint performance. METHODS: The acceleration and maximal running velocity developed by 11 subjects (age 16 +/- 1) during a 40-m sprint were measured by radar. Their leg muscle volumes were estimated anthropometrically. Leg power was measured by an ergometric treadmill test and by a hopping test. Each subject executed a maximal sprint acceleration on the treadmill equipped with force and speed transducers, from which forward power was calculated. A hopping jump test was executed at 2 Hz on a force platform. Leg stiffness was calculated using the flight and contact times of the hopping test. RESULTS: The treadmill forward leg power was correlated with both the initial acceleration (r = 0.80, P < 0.01) and the maximal running velocity (r = 0.73, P < 0.05) during track sprinting. The leg stiffness calculated from hopping was significantly correlated with the maximal velocity but not with acceleration. CONCLUSION: Although muscle power is needed for acceleration and maintaining a maximal velocity in sprint performance, high leg stiffness may be needed for high running speed. The ability to produce a stiff rebound during the maximal running velocity could be explored by measuring the stiffness of a rebound during a vertical jump.
Starting from standing; why step backwards?
J Biomech. 2001 Feb;34(2):211-5.
At push-off, the mass centre of gravity of the body must be positioned in front of the foot to prevent a somersault. When starting a sprint from out the standing position the use of a step backwards is necessary for maximal acceleration. The aim of the present study was to quantify the positive contribution to push off from a backward step of the leg, which seems to be counterproductive. Ten subjects were instructed to sprint start in three different ways: (a) starting from the standing position just in front of the force platform on the subject's own initiative, (b) starting from the standing position on the force platform with no step backward allowed, and (c) starting out of the starting position with one leg in front of the force platform and the push-off leg on the force platform. A step backwards was observed in 95% of the starts from the standing position. The push-off force was highest in starting type (a), which had the shortest time to build up the push-off force. The results indicate a positive contribution to the force and power from a step backwards. We advocate developing a training program with special attention to the phenomenon step backwards.
Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?
Med Sci Sports Exerc. 2000 Mar;32(3):647-53.
PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.
Sprint performance is related to muscle fascicle length in male 100-m sprinters.
J Appl Physiol. 2000 Mar;88(3):811-6.
The purpose of this study was to investigate the relationship between muscle fascicle length and sprint running performance in 37 male 100-m sprinters. The sample was divided into two performance groups by the personal-best 100-m time: 10.00-10.90 s (S10; n = 22) and 11.00-11.70 s (S11; n = 15). Muscle thickness and fascicle pennation angle of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Standing height, body weight, and leg length were similar between groups. Muscle thickness was similar between groups for vastus lateralis and gastrocnemius medialis, but S10 had a significantly greater gastrocnemius lateralis muscle thickness. S10 also had a greater muscle thickness in the upper portion of the thigh, which, given similar limb lengths, demonstrates an altered "muscle shape." Pennation angle was always less in S10 than in S11. In all muscles, S10 had significantly greater fascicle length than did S11, which significantly correlated with 100-m best performance (r values from -0.40 to -0.57). It is concluded that longer fascicle length is associated with greater sprinting performance.
Changes in performance, muscle metabolites, enzymes and fibre types after short sprint training.
Eur J Appl Physiol Occup Physiol. 1998 Jul;78(2):163-9.
In contrast to endurance training, little research has been carried out to investigate the effects of short (< 10 s) sprint training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30-80 m at 90-100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance (maximal oxygen consumption; VO2max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 x 40 m sprints, 24 s recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis) were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and VO2max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.
Influence of strength training on sprint running performance. Current findings and implications for training.
Sports Med. 1997 Sep;24(3):147-56. Review.
Today, it is generally accepted that sprint performance, like endurance performance, can improve considerably with training. Strength training, especially, plays a key role in this process. Sprint performance will be viewed multidimensionally as an initial acceleration phase (0 to 10 m), a phase of maximum running speed (36 to 100 m) and a transition phase in between. Immediately following the start action, the powerful extensions of the hip, knee and ankle joints are the main accelerators of body mass. However, the hamstrings, the m. adductor magnus and the m. gluteus maximus are considered to make the most important contribution in producing the highest levels of speed. Different training methods are proposed to improve the power output of these muscles. Some of them aim for hypertrophy and others for specific adaptations of the nervous system. This includes general (hypertrophy and neuronal activation), velocity specific (speed-strength) and movement specific (sprint associated exercises) strength training. In developing training strategies, the coach has to keep in mind that strength, power and speed are inherently related to one another, because they are all the output of the same functional systems. As heavy resistance training results in a fibre type IIb into fibre type IIa conversion, the coach has to aim for an optimal balance between sprint specific and nonspecific training components. To achieve this they must take into consideration the specific strength training demands of each individual, based on performance capacity in each specific phase of the sprint.
Biomechanics of the sprint start.
Sports Med. 1997 Jan;23(1):11-20.
Many variables have been studied pertaining to the block sprint start. Research suggests that the adoption of a medium block spacing is preferred, with front and rear knee angles in the set position approximating 90 and 130 degrees, respectively, with the hips held moderately high. The sprinter must be capable of developing a high force rate combined with a high maximum force, especially in the horizontal direction. This ability to create high force underlies other important indicators of starting performance such as minimum block clearance time, maximum block leaving velocity and maximum block leaving acceleration. Once the sprinter has projected him/herself from the blocks at a low angle (40 to 45 degrees) relative to the ground, the following 2 post-block steps should occur with the total body centre of gravity ahead of the contacting foot at foot strike to minimise potential horizontal braking forces.
Influence of high-resistance and high-velocity training on sprint performance.
Med Sci Sports Exerc. 1995 Aug;27(8):1203-9.
The purpose of this study is to analyze the effect of high-resistance (HR) and high-velocity (HV) training on the different phases of 100-m sprint performance. Two training groups (HR and HV) were compared with two control groups (RUN and PAS). The HR (N = 22) and HV group (N = 21) trained 3 d.wk-1 for 9 wk: two strength training sessions (HR or HV) and one running session. There was a run control group (RUN, N = 12) that also participated in the running sessions (1 d.wk-1) and a passive control group (PAS, N = 11). Running speed over a 100-m sprint was recorded every 2 m. By means of a principal component analysis on all speed variables, three phases were distinguished: initial acceleration (0-10 m), building-up running speed to a maximum (10-36 m), and maintaining maximum speed in the second part of the run (36-100 m). HV training resulted in improved initial acceleration (P < 0.05 compared with RUN, PAS, and HR), a higher maximum speed (P < 0.05 compared with PAS), and a decreased speed endurance (P < 0.05 compared to RUN and PAS). The HV group improved significantly in total 100 m time (P < 0.05 compared with the RUN and PAS groups). The HR program resulted in an improved initial acceleration phase (P < 0.05 compared with PAS).
Relationship between strength qualities and sprinting performance.
J Sports Med Phys Fitness. 1995 Mar;35(1):13-9.
The purpose of this study was to investigate the relationship between strength measures and sprinting performance, and to determine if these relationships varied for different phases of sprint running. Twenty (11 males and 9 females) elite junior track and field athletes served as subjects. Athletes performed maximum sprints to 50 m from a block start and time to 2.5, 5, 10, 20, 30, 40 and 50 m were recorded by electronic timing gates. The resultant forces applied to the blocks were obtained from two force platforms. Twenty-seven measures of strength and speed-strength (absolute and relative to bodyweight) were collected from the height jumped and the force-time curve recorded from the takeoff phase of vertical jumping movements utilizing pure concentric, stretch shortening cycle (SSC) and isometric muscular contractions. Pearson correlation analysis revealed that the single best predictor of starting performance (2.5 m time) was the peak force (relative to bodyweight) generated during a jump from a 120 degree knee angle (concentric contraction) (r = 0.86, p = 0.0001). The single best correlate of maximum sprinting speed was the force applied at 100 ms (relative to bodyweight) from the start of a loaded jumping action (concentric contraction) (r = 0.80, p = 0.0001). SSC measures and maximum absolute strength were more related to maximum sprinting speed than starting ability. It was concluded that strength qualities were related to sprinting performance and these relationships differed for starting and maximum speed sprinting.
Sprint-training effects on some contractile properties of single skinned human muscle fibres.
Acta Physiol Scand. 1994 Nov;152(3):295-306.
The effects of sprint training on the contractile properties of human muscle fibres obtained by needle biopsy were investigated. Individual fibres were mechanically skinned and activated by Ca(2+)- and Sr(2+)-buffered solutions at pH 7.1, and allocated to distinct populations on the basis of their contractile characteristics. The majority of fibres sampled pre-training could be separated into the three major fibre groups: Populations I (24/70, 34%), II (25/70, 36%) and III (18/70, 26%), which exhibited characteristics similar to those of histochemically classified type I, IIA and IIB fibres, respectively. The remainder (3/70, 4%) represented another fibre group, with intermediate characteristics. The muscle fibres were also activated by Ca2+ at a reduced pH of 6.6, to mimic the intracellular acidification that occurs during intense exercise. Lowering pH increased the threshold for contraction by Ca2+, reduced Ca2+ sensitivity, and increased the steepness of the force-pCa relationship, in all fibres sampled from the three major fibre groups. Maximum force was not significantly reduced in any fibre population. In the post-training sample, the three major fibre types were present in different proportions: Populations I (10/52, 19%), II (20/52, 38.5%) and III (11/52, 21%). Three other fibre groups sampled in low numbers exhibited contractile characteristics intermediate between Population I and Population II. Following sprint training all of the three main fibre populations exhibited higher thresholds for contraction by, and lower sensitivities to, Sr2+ but not Ca2+, compared with the fibres sampled pre-training. Maximum force was significantly lower in Population II fibres after sprint training. At pH 6.6, post-trained Population III fibres exhibited even lower Ca2+ sensitivity, with concomitant increases in the threshold for contraction and force-pCa curve steepness.
The optimal training load for the development of dynamic athletic performance.
Med Sci Sports Exerc. 1993 Nov;25(11):1279-86.
This study was performed to determine which of three theoretically optimal resistance training modalities resulted in the greatest enhancement in the performance of a series of dynamic athletic activities. The three training modalities included 1) traditional weight training, 2) plyometric training, and 3) explosive weight training at the load that maximized mechanical power output. Sixty-four previously trained subjects were randomly allocated to four groups that included the above three training modalities and a control group. The experimental groups trained for 10 wk performing either heavy squat lifts, depth jumps, or weighted squat jumps. All subjects were tested prior to training, after 5 wk of training and at the completion of the training period. The test items included 1) 30-m sprint, 2) vertical jumps performed with and without a countermovement, 3) maximal cycle test, 4) isokinetic leg extension test, and 5) a maximal isometric test. The experimental group which trained with the load that maximized mechanical power achieved the best overall results in enhancing dynamic athletic performance recording statistically significant (P < 0.05) improvements on most test items and producing statistically superior results to the two other training modalities on the jumping and isokinetic tests.
Function of mono- and biarticular muscles in running.
Med Sci Sports Exerc. 1993 Oct;25(10):1163-73.
In this study the function of leg muscles during stretch-shortening cycles in fast running (6 m.s-1) was investigated. For a single stance phase, kinematics, ground reaction forces, and EMG were recorded. First, rough estimates of muscle force, obtained by shifting the EMG curves +90 ms, were correlated with origin-to-insertion velocity (VOI). Second, active state and internal muscle behavior were estimated by using a muscle model that was applied for soleus and gastrocnemius. High correlations were found between estimates of muscle force and VOI time curves for mono-articular hip, knee, and ankle extensor muscles. The correlation coefficients for biarticular muscles were low. The model results showed that active state of gastrocnemius was high during increase of origin-to-insertion length (LOI), whereas active state of soleus was low during the start of increase of LOI and rose to a plateau at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a compromise between minimizing energy dissipation and using the stretch-shortening cycle optimally. Furthermore, it was found that the net plantar flexion moment during running reached a value of 302 Nm, which was 158% and 127% higher than the peak values reached in maximal jump and sprint push-offs, respectively. It was argued that the higher mechanical output in running than in jumping could be ascribed to the utilization of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.
Biomechanics of sprint running. A review.
Sports Med. 1992 Jun;13(6):376-92. Review.
Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.
Activity of mono- and biarticular leg muscles during sprint running.
Eur J Appl Physiol Occup Physiol. 1985;54(5):524-32.
A cinematographic recording of the movements of the lower limbs together with simultaneous emg tracings from nine lower limb muscles were obtained from two male track sprinters during three phases of a 100 m sprint run. The extensor muscles of the hip joint were found to be the primary movers by acceleration of the body's center of gravity (C.G.) during the ground phase of the running cycle. The extensors of the knee joint were also important in this, but to a minor extent, while the plantar flexors of the ankle joint showed the least contribution. The biarticular muscles functioned in a way different from the monoarticular muscles in the sense that they perform eccentric work during the flight and recovery phases and concentric work during the whole ground phase (support), whereas the monoarticular muscles are restricted first to eccentric work and then to concentric work during the ground phase. Furthermore, the biarticular muscles show variation (and rate of variation) in muscle length to a larger extent than the monoarticular muscles. Paradoxical muscle actions appear to take place around the knee joint, where the hamstring muscles, m. gastrocnemius, m. vastus laterialis and m. vastus medialis act as synergists by extending the knee joint during the last part of the ground phase.
J Sports Med Phys Fitness. 2008 Mar;48(1):49-54.
The present findings suggest that the ability to produce force quickly, as measured by the time to achieve 60% of maximum voluntary contraction is related to sprinting performance, with the coefficient of determination accounting for 53% of the variance in the data. These data also show that sprinting ability is linked with DJ performance, especially the drop jump from a height of 30 cm (11.8 in).
Effects of sprint and plyometric training on muscle function and athletic performance.
J Strength Cond Res. 2007 May;21(2):543-9.
We conclude that short-term sprint training produces similar or even greater training effects in muscle function and athletic performance than does conventional plyometric training. This study provides support for the use of sprint training as an applicable training method of improving explosive performance of athletes in general.
The relationship between maximal jump-squat power and sprint acceleration in athletes.
Eur J Appl Physiol. 2004 Jan;91(1):46-52.
Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.
Relationship between strength qualities and sprinting performance.
J Sports Med Phys Fitness. 1995 Mar;35(1):13-9.
The single best correlate of maximum sprinting speed was the force applied at 100 ms (relative to bodyweight) from the start of a loaded jumping action (concentric contraction) (r = 0.80, p = 0.0001). SSC measures and maximum absolute strength were more related to maximum sprinting speed than starting ability. It was concluded that strength qualities were related to sprinting performance and these relationships differed for starting and maximum speed sprinting.
The contribution of maximal force production to explosive movement among young collegiate athletes.
J Strength Cond Res. 2006 Nov;20(4):867-73.
Muscular strength, peak power output, vertical jumping ability, standing broad jump, agility, sprint acceleration, and sprint velocity were all shown to be very highly related. Further examination demonstrated that body mass-adjusted muscular strength is more highly related to performance measures than is absolute muscular strength.
A comparison of drop jump training methods: effects on leg extensor strength qualities and jumping performance.
Int J Sports Med. 1999 Jul;20(5):295-303.
It was concluded that DJ-H/t method was effective for the development of RS, but training with DJ-H was not intense and/or specific enough to stimulate gains in strength qualities of the leg extensors or jumping performance.
- key words: sprint running -
Effects of sprint and plyometric training on muscle function and athletic performance.
J Strength Cond Res. 2007 May;21(2):543-9.
We conclude that short-term sprint training produces similar or even greater training effects in muscle function and athletic performance than does conventional plyometric training. This study provides support for the use of sprint training as an applicable training method of improving explosive performance of athletes in general.
Aging, muscle fiber type, and contractile function in sprint-trained athletes.
J Appl Physiol. 2006 Sep;101(3):906-17. Epub 2006 May 11.
The sprint-trained athletes experienced the typical aging-related reduction in the size of fast fibers, a shift toward a slower MHC isoform profile, and a lower V(o) of type I MHC fibers, which played a role in the decline in explosive force production. However, the muscle characteristics were preserved at a high level in the oldest runners, underlining the favorable impact of sprint exercise on aging muscle.
Effects of hip flexor training on sprint, shuttle run, and vertical jump performance.
J Strength Cond Res. 2005 Aug;19(3):615-21.
Individuals in the training group improved hip flexion strength by 12.2% and decreased their 40-yd and shuttle run times by 3.8% and 9.0%, respectively. An increase in hip flexion strength can help to improve sprint and agility performance for physically active, untrained individuals.
Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players.
Br J Sports Med. 2004 Jun;38(3):285-8.
Maximal strength in half squats determines sprint performance and jumping height in high level soccer players. High squat strength did not imply reduced maximal oxygen consumption. Elite soccer players should focus on maximal strength training, with emphasis on maximal mobilisation of concentric movements, which may improve their sprinting and jumping performance.
Which starting style is faster in sprint running - standing or crouch start?
Sports Biomech. 2004 Jan;3(1):43-53.
Six university track team sprinters performed 2 x 3 x 50 m trials...during the first steps of the performance the standing start produced higher body centre of mass horizontal velocity than the crouch start. This may be due to the longer distance between the feet in the standing start, which caused longer push-off phases, and the work against gravity in the crouch start. However, this advantage in horizontal velocity disappeared by the 10 m mark, where similar velocities were recorded with both start styles. Further, there was no statistically significant difference between the two starting styles in horizontal velocity at the 25 m mark, nor in the time to reach the 25 m or 50 m mark.
Interaction of step length and step rate during sprint running.
Med Sci Sports Exerc. 2004 Feb;36(2):261-71.
A "negative interaction" between step length and step rate refers to an increase in one factor resulting in a decrease in the other...A wide range of step length and step rate combinations was evident, even for subgroups of athletes with similar sprint velocities. This was partly due to a negative interaction that existed between step length and step rate; that is, those athletes who used a longer step length tended to have a lower step rate and vice versa. Vertical velocity of takeoff was the most prominent source of the negative interaction.
The relationship between maximal jump-squat power and sprint acceleration in athletes.
Eur J Appl Physiol. 2004 Jan;91(1):46-52. Epub 2003 Sep 24.
This study investigated the relationship between sprint start performance (5-m time) and strength and power variables. Thirty male athletes [height: 183.8 (6.8) cm, and mass: 90.6 (9.3) kg; mean (SD)] each completed six 10-m sprints from a standing start...Three to six days later subjects completed three concentric jump squats, using a traditional and split technique, at a range of external loads from 30-70% of one repetition maximum (1RM)...Average and peak power were similar during the split squat and the traditional squat and both were significantly related to 5-m time ( r=-0.64 to -0.68, P<0.001)...Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.
Age-related differences in 100-m sprint performance in male and female master runners.
Med Sci Sports Exerc. 2003 Aug;35(8):1419-28.
There was a general decline in sprint performances with age, the decrease becoming more evident around 65-70 yr of age. The velocity during the different phases of the run declined on average from 5 to 6% per decade in males and from 5 to 7% per decade in females. Similarly, SL showed clear reductions with increasing age, whereas SR remained unchanged until the oldest age groups in both genders. Furthermore, the CT, which correlated with velocity, was significantly longer, and FT, which correlated with both velocity and SL, was shorter in older age groups. CONCLUSION: Our findings indicated that age-associated differences in velocity in elite master sprinters were similar in each phase of the 100-m run. The deterioration of the overall performance with age was primarily related to reduction in SL and increase in CT.
Effect of the movement speed of resistance training exercises on sprint and strength performance in concurrently training elite junior sprinters.
J Sports Sci. 2002 Dec;20(12):981-90.
The aim of this study was to determine the effects of 7 weeks of high- and low-velocity resistance training on strength and sprint running performance in nine male elite junior sprint runners (age 19.0+/-1.4 years, best 100 m times 10.89+/-0.21 s; mean +/- s). The athletes continued their sprint training throughout the study, but their resistance training programme was replaced by one in which the movement velocities of hip extension and flexion, knee extension and flexion and squat exercises varied according to the loads lifted (i.e. 30-50% and 70-90% of 1-RM in the high- and low-velocity training groups, respectively). There were no between-group differences in hip flexion or extension torque produced at 1.05, 4.74 or 8.42 rad x s(-1), 20 m acceleration or 20 m 'flying' running times, or 1-RM squat lift strength either before or after training. This was despite significant improvements in 20 m acceleration time (P < 0.01), squat strength (P < 0.05), isokinetic hip flexion torque at 4.74 rad x s(-1) and hip extension torque at 1.05 and 4.74 rad x s(-1) for the athletes as a whole over the training period. Although velocity-specific strength adaptations have been shown to occur rapidly in untrained and nonconcurrently training individuals, the present results suggest a lack of velocity-specific performance changes in elite concurrently training sprint runners performing a combination of traditional and semi-specific resistance training exercises.
Leg strength and stiffness as ability factors in 100 m sprint running.
J Sports Med Phys Fitness. 2002 Sep;42(3):274-81.
BACKGROUND: The purpose of this study was to determine the importance of leg strength and stiffness relative to i) 100 m sprint performance, ii) mean speed on the three phases of the 100 m race (30-60-100 m) and iii) the speed differences between these phases. METHODS: Nineteen regional to national level male sprinters competed in a 100 m race. Video analysis was used to determine mean velocity parameters. Two subgroups were created since some of the runners decreased their velocity during the third phase (G1), whereas others maintained or accelerated it (G2). Leg strength (concentric half-squats - counter movement jump) and stiffness (hopping) were determined. RESULTS: The mean performance over 100 m was 11.43 sec (10.72-12.87 sec). The concentric half-squats were related to 100 m (r=0.74, p<0.001) and to the mean speed of each phase (R=0.75, p<0.01). The counter movement jump was related to 100 m (r=0.57, p<0.05) and was the predictor of the first phase (r=0.66, p<0.01). The hopping test was the predictor of the two last phases (R=0.66, p<0.05). Athletes who had the greatest leg stiffness (G1) produced the highest acceleration between the first and the second phases, and presented a deceleration between the second and the third ones.
Long-term metabolic and skeletal muscle adaptations to short-sprint training: implications for sprint training and tapering.
Sports Med. 2001;31(15):1063-82. Review.
The adaptations of muscle to sprint training can be separated into metabolic and morphological changes. Enzyme adaptations represent a major metabolic adaptation to sprint training, with the enzymes of all three energy systems showing signs of adaptation to training and some evidence of a return to baseline levels with detraining. Myokinase and creatine phosphokinase have shown small increases as a result of short-sprint training in some studies and elite sprinters appear better able to rapidly breakdown phosphocreatine (PCr) than the sub-elite. No changes in these enzyme levels have been reported as a result of detraining. Similarly, glycolytic enzyme activity (notably lactate dehydrogenase, phosphofructokinase and glycogen phosphorylase) has been shown to increase after training consisting of either long (>10-second) or short (<10-second) sprints. Evidence suggests that these enzymes return to pre-training levels after somewhere between 7 weeks and 6 months of detraining. Mitochondrial enzyme activity also increases after sprint training, particularly when long sprints or short recovery between short sprints are used as the training stimulus. Morphological adaptations to sprint training include changes in muscle fibre type, sarcoplasmic reticulum, and fibre cross-sectional area. An appropriate sprint training programme could be expected to induce a shift toward type IIa muscle, increase muscle cross-sectional area and increase the sarcoplasmic reticulum volume to aid release of Ca(2+). Training volume and/or frequency of sprint training in excess of what is optimal for an individual, however, will induce a shift toward slower muscle contractile characteristics. In contrast, detraining appears to shift the contractile characteristics towards type IIb, although muscle atrophy is also likely to occur. Muscle conduction velocity appears to be a potential non-invasive method of monitoring contractile changes in response to sprint training and detraining. In summary, adaptation to sprint training is clearly dependent on the duration of sprinting, recovery between repetitions, total volume and frequency of training bouts. These variables have profound effects on the metabolic, structural and performance adaptations from a sprint-training programme and these changes take a considerable period of time to return to baseline after a period of detraining. However, the complexity of the interaction between the aforementioned variables and training adaptation combined with individual differences is clearly disruptive to the transfer of knowledge and advice from laboratory to coach to athlete.
Relationship of the stretch-shortening cycle to sprint performance in trained female athletes.
J Strength Cond Res. 2001 Aug;15(3):326-31.
Seventeen trained, female, high school, competitive sprinters completed the following tests: countermovement jump for vertical distance (CMJ), bounce drop jump for height with minimum ground contact time (BDJ index), and ground contact time (GCT) during the BDJ and a 5-step bound (5B) test...Sprint performances at 30-, 100-, and 300-m distances were assessed...Significant correlations (p < 0.05) existed between CMJ and 30-m (r = -0.60), 100-m (r = -0.64), and 300-m (r = -0.55) sprint times; BDJ index and 30-m (r = -0.79) and 100-m (r = -0.75) sprint times; and 5B test and 300-m sprint time (r = -0.54)...Results indicated that the BDJ index and CMJ tests were significantly related to sprint performances in female athletes.
Neural influences on sprint running: training adaptations and acute responses.
Sports Med. 2001;31(6):409-25. Review.
Performance in sprint exercise is determined by the ability to accelerate, the magnitude of maximal velocity and the ability to maintain velocity against the onset of fatigue. These factors are strongly influenced by metabolic and anthropometric components. Improved temporal sequencing of muscle activation and/or improved fast twitch fibre recruitment may contribute to superior sprint performance. Speed of impulse transmission along the motor axon may also have implications on sprint performance. Nerve conduction velocity (NCV) has been shown to increase in response to a period of sprint training. However, it is difficult to determine if increased NCV is likely to contribute to improved sprint performance. An increase in motoneuron excitability, as measured by the Hoffman reflex (H-reflex), has been reported to produce a more powerful muscular contraction, hence maximising motoneuron excitability would be expected to benefit sprint performance. Motoneuron excitability can be raised acutely by an appropriate stimulus with obvious implications for sprint performance. However, at rest H-reflex has been reported to be lower in athletes trained for explosive events compared with endurance-trained athletes. This may be caused by the relatively high, fast twitch fibre percentage and the consequent high activation thresholds of such motor units in power-trained populations. In contrast, stretch reflexes appear to be enhanced in sprint athletes possibly because of increased muscle spindle sensitivity as a result of sprint training. With muscle in a contracted state, however, there is evidence to suggest greater reflex potentiation among both sprint and resistance-trained populations compared with controls. Again this may be indicative of the predominant types of motor units in these populations, but may also mean an enhanced reflex contribution to force production during running in sprint-trained athletes. Fatigue of neural origin both during and following sprint exercise has implications with respect to optimising training frequency and volume. Research suggests athletes are unable to maintain maximal firing frequencies for the full duration of, for example, a 100m sprint. Fatigue after a single training session may also have a neural manifestation with some athletes unable to voluntarily fully activate muscle or experiencing stretch reflex inhibition after heavy training. This may occur in conjunction with muscle damage. Research investigating the neural influences on sprint performance is limited. Further longitudinal research is necessary to improve our understanding of neural factors that contribute to training-induced improvements in sprint performance.
Muscle power patterns in the mid-acceleration phase of sprinting.
J Sports Sci. 2001 Apr;19(4):263-72.
To assess the role of the lower limb joints in generating velocity in the mid-acceleration phase of sprinting, muscle power patterns of the hip, knee and ankle were determined. Six male sprinters with a mean 100 m time of 10.75 s performed repeated maximal sprints along a 35 m indoor track. A complete stride across a force platform, positioned at approximately 14 m into the sprint, was video-recorded for analysis. Smoothed coordinate data were obtained from manual digitization of (50 Hz) video images and were then interpolated to match the sampling rate of the recorded ground reaction force (1000 Hz). The moment at each joint was then calculated using inverse dynamics and multiplied by the angular velocity to determine the muscle power. The results showed a proximal-to-distal timing in the generation of peak extensor power during stance at the hip, the knee and then the ankle, with the plantar flexors producing the greatest peak power. Apart from a moderate power generation peak towards toe-off, knee power was negligible despite a large extensor moment throughout stance. The role of the knee thus appears to be one of maintaining the centre of mass height and enabling the power generated at the hip to be transferred to the ankle.
Leg power and hopping stiffness: relationship with sprint running performance.
Med Sci Sports Exerc. 2001 Feb;33(2):326-33.
PURPOSE: Although sprint performance undoubtedly involves muscle power, the stiffness of the leg also determines sprint performance while running at maximal velocity. Results that include both of these characteristics have not been directly obtained in previous studies on human runners. We have therefore studied the link between leg power, leg stiffness, and sprint performance. METHODS: The acceleration and maximal running velocity developed by 11 subjects (age 16 +/- 1) during a 40-m sprint were measured by radar. Their leg muscle volumes were estimated anthropometrically. Leg power was measured by an ergometric treadmill test and by a hopping test. Each subject executed a maximal sprint acceleration on the treadmill equipped with force and speed transducers, from which forward power was calculated. A hopping jump test was executed at 2 Hz on a force platform. Leg stiffness was calculated using the flight and contact times of the hopping test. RESULTS: The treadmill forward leg power was correlated with both the initial acceleration (r = 0.80, P < 0.01) and the maximal running velocity (r = 0.73, P < 0.05) during track sprinting. The leg stiffness calculated from hopping was significantly correlated with the maximal velocity but not with acceleration. CONCLUSION: Although muscle power is needed for acceleration and maintaining a maximal velocity in sprint performance, high leg stiffness may be needed for high running speed. The ability to produce a stiff rebound during the maximal running velocity could be explored by measuring the stiffness of a rebound during a vertical jump.
Starting from standing; why step backwards?
J Biomech. 2001 Feb;34(2):211-5.
At push-off, the mass centre of gravity of the body must be positioned in front of the foot to prevent a somersault. When starting a sprint from out the standing position the use of a step backwards is necessary for maximal acceleration. The aim of the present study was to quantify the positive contribution to push off from a backward step of the leg, which seems to be counterproductive. Ten subjects were instructed to sprint start in three different ways: (a) starting from the standing position just in front of the force platform on the subject's own initiative, (b) starting from the standing position on the force platform with no step backward allowed, and (c) starting out of the starting position with one leg in front of the force platform and the push-off leg on the force platform. A step backwards was observed in 95% of the starts from the standing position. The push-off force was highest in starting type (a), which had the shortest time to build up the push-off force. The results indicate a positive contribution to the force and power from a step backwards. We advocate developing a training program with special attention to the phenomenon step backwards.
Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?
Med Sci Sports Exerc. 2000 Mar;32(3):647-53.
PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.
Sprint performance is related to muscle fascicle length in male 100-m sprinters.
J Appl Physiol. 2000 Mar;88(3):811-6.
The purpose of this study was to investigate the relationship between muscle fascicle length and sprint running performance in 37 male 100-m sprinters. The sample was divided into two performance groups by the personal-best 100-m time: 10.00-10.90 s (S10; n = 22) and 11.00-11.70 s (S11; n = 15). Muscle thickness and fascicle pennation angle of the vastus lateralis and gastrocnemius medialis and lateralis muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Standing height, body weight, and leg length were similar between groups. Muscle thickness was similar between groups for vastus lateralis and gastrocnemius medialis, but S10 had a significantly greater gastrocnemius lateralis muscle thickness. S10 also had a greater muscle thickness in the upper portion of the thigh, which, given similar limb lengths, demonstrates an altered "muscle shape." Pennation angle was always less in S10 than in S11. In all muscles, S10 had significantly greater fascicle length than did S11, which significantly correlated with 100-m best performance (r values from -0.40 to -0.57). It is concluded that longer fascicle length is associated with greater sprinting performance.
Changes in performance, muscle metabolites, enzymes and fibre types after short sprint training.
Eur J Appl Physiol Occup Physiol. 1998 Jul;78(2):163-9.
In contrast to endurance training, little research has been carried out to investigate the effects of short (< 10 s) sprint training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30-80 m at 90-100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance (maximal oxygen consumption; VO2max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 x 40 m sprints, 24 s recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis) were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and VO2max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.
Influence of strength training on sprint running performance. Current findings and implications for training.
Sports Med. 1997 Sep;24(3):147-56. Review.
Today, it is generally accepted that sprint performance, like endurance performance, can improve considerably with training. Strength training, especially, plays a key role in this process. Sprint performance will be viewed multidimensionally as an initial acceleration phase (0 to 10 m), a phase of maximum running speed (36 to 100 m) and a transition phase in between. Immediately following the start action, the powerful extensions of the hip, knee and ankle joints are the main accelerators of body mass. However, the hamstrings, the m. adductor magnus and the m. gluteus maximus are considered to make the most important contribution in producing the highest levels of speed. Different training methods are proposed to improve the power output of these muscles. Some of them aim for hypertrophy and others for specific adaptations of the nervous system. This includes general (hypertrophy and neuronal activation), velocity specific (speed-strength) and movement specific (sprint associated exercises) strength training. In developing training strategies, the coach has to keep in mind that strength, power and speed are inherently related to one another, because they are all the output of the same functional systems. As heavy resistance training results in a fibre type IIb into fibre type IIa conversion, the coach has to aim for an optimal balance between sprint specific and nonspecific training components. To achieve this they must take into consideration the specific strength training demands of each individual, based on performance capacity in each specific phase of the sprint.
Biomechanics of the sprint start.
Sports Med. 1997 Jan;23(1):11-20.
Many variables have been studied pertaining to the block sprint start. Research suggests that the adoption of a medium block spacing is preferred, with front and rear knee angles in the set position approximating 90 and 130 degrees, respectively, with the hips held moderately high. The sprinter must be capable of developing a high force rate combined with a high maximum force, especially in the horizontal direction. This ability to create high force underlies other important indicators of starting performance such as minimum block clearance time, maximum block leaving velocity and maximum block leaving acceleration. Once the sprinter has projected him/herself from the blocks at a low angle (40 to 45 degrees) relative to the ground, the following 2 post-block steps should occur with the total body centre of gravity ahead of the contacting foot at foot strike to minimise potential horizontal braking forces.
Influence of high-resistance and high-velocity training on sprint performance.
Med Sci Sports Exerc. 1995 Aug;27(8):1203-9.
The purpose of this study is to analyze the effect of high-resistance (HR) and high-velocity (HV) training on the different phases of 100-m sprint performance. Two training groups (HR and HV) were compared with two control groups (RUN and PAS). The HR (N = 22) and HV group (N = 21) trained 3 d.wk-1 for 9 wk: two strength training sessions (HR or HV) and one running session. There was a run control group (RUN, N = 12) that also participated in the running sessions (1 d.wk-1) and a passive control group (PAS, N = 11). Running speed over a 100-m sprint was recorded every 2 m. By means of a principal component analysis on all speed variables, three phases were distinguished: initial acceleration (0-10 m), building-up running speed to a maximum (10-36 m), and maintaining maximum speed in the second part of the run (36-100 m). HV training resulted in improved initial acceleration (P < 0.05 compared with RUN, PAS, and HR), a higher maximum speed (P < 0.05 compared with PAS), and a decreased speed endurance (P < 0.05 compared to RUN and PAS). The HV group improved significantly in total 100 m time (P < 0.05 compared with the RUN and PAS groups). The HR program resulted in an improved initial acceleration phase (P < 0.05 compared with PAS).
Relationship between strength qualities and sprinting performance.
J Sports Med Phys Fitness. 1995 Mar;35(1):13-9.
The purpose of this study was to investigate the relationship between strength measures and sprinting performance, and to determine if these relationships varied for different phases of sprint running. Twenty (11 males and 9 females) elite junior track and field athletes served as subjects. Athletes performed maximum sprints to 50 m from a block start and time to 2.5, 5, 10, 20, 30, 40 and 50 m were recorded by electronic timing gates. The resultant forces applied to the blocks were obtained from two force platforms. Twenty-seven measures of strength and speed-strength (absolute and relative to bodyweight) were collected from the height jumped and the force-time curve recorded from the takeoff phase of vertical jumping movements utilizing pure concentric, stretch shortening cycle (SSC) and isometric muscular contractions. Pearson correlation analysis revealed that the single best predictor of starting performance (2.5 m time) was the peak force (relative to bodyweight) generated during a jump from a 120 degree knee angle (concentric contraction) (r = 0.86, p = 0.0001). The single best correlate of maximum sprinting speed was the force applied at 100 ms (relative to bodyweight) from the start of a loaded jumping action (concentric contraction) (r = 0.80, p = 0.0001). SSC measures and maximum absolute strength were more related to maximum sprinting speed than starting ability. It was concluded that strength qualities were related to sprinting performance and these relationships differed for starting and maximum speed sprinting.
Sprint-training effects on some contractile properties of single skinned human muscle fibres.
Acta Physiol Scand. 1994 Nov;152(3):295-306.
The effects of sprint training on the contractile properties of human muscle fibres obtained by needle biopsy were investigated. Individual fibres were mechanically skinned and activated by Ca(2+)- and Sr(2+)-buffered solutions at pH 7.1, and allocated to distinct populations on the basis of their contractile characteristics. The majority of fibres sampled pre-training could be separated into the three major fibre groups: Populations I (24/70, 34%), II (25/70, 36%) and III (18/70, 26%), which exhibited characteristics similar to those of histochemically classified type I, IIA and IIB fibres, respectively. The remainder (3/70, 4%) represented another fibre group, with intermediate characteristics. The muscle fibres were also activated by Ca2+ at a reduced pH of 6.6, to mimic the intracellular acidification that occurs during intense exercise. Lowering pH increased the threshold for contraction by Ca2+, reduced Ca2+ sensitivity, and increased the steepness of the force-pCa relationship, in all fibres sampled from the three major fibre groups. Maximum force was not significantly reduced in any fibre population. In the post-training sample, the three major fibre types were present in different proportions: Populations I (10/52, 19%), II (20/52, 38.5%) and III (11/52, 21%). Three other fibre groups sampled in low numbers exhibited contractile characteristics intermediate between Population I and Population II. Following sprint training all of the three main fibre populations exhibited higher thresholds for contraction by, and lower sensitivities to, Sr2+ but not Ca2+, compared with the fibres sampled pre-training. Maximum force was significantly lower in Population II fibres after sprint training. At pH 6.6, post-trained Population III fibres exhibited even lower Ca2+ sensitivity, with concomitant increases in the threshold for contraction and force-pCa curve steepness.
The optimal training load for the development of dynamic athletic performance.
Med Sci Sports Exerc. 1993 Nov;25(11):1279-86.
This study was performed to determine which of three theoretically optimal resistance training modalities resulted in the greatest enhancement in the performance of a series of dynamic athletic activities. The three training modalities included 1) traditional weight training, 2) plyometric training, and 3) explosive weight training at the load that maximized mechanical power output. Sixty-four previously trained subjects were randomly allocated to four groups that included the above three training modalities and a control group. The experimental groups trained for 10 wk performing either heavy squat lifts, depth jumps, or weighted squat jumps. All subjects were tested prior to training, after 5 wk of training and at the completion of the training period. The test items included 1) 30-m sprint, 2) vertical jumps performed with and without a countermovement, 3) maximal cycle test, 4) isokinetic leg extension test, and 5) a maximal isometric test. The experimental group which trained with the load that maximized mechanical power achieved the best overall results in enhancing dynamic athletic performance recording statistically significant (P < 0.05) improvements on most test items and producing statistically superior results to the two other training modalities on the jumping and isokinetic tests.
Function of mono- and biarticular muscles in running.
Med Sci Sports Exerc. 1993 Oct;25(10):1163-73.
In this study the function of leg muscles during stretch-shortening cycles in fast running (6 m.s-1) was investigated. For a single stance phase, kinematics, ground reaction forces, and EMG were recorded. First, rough estimates of muscle force, obtained by shifting the EMG curves +90 ms, were correlated with origin-to-insertion velocity (VOI). Second, active state and internal muscle behavior were estimated by using a muscle model that was applied for soleus and gastrocnemius. High correlations were found between estimates of muscle force and VOI time curves for mono-articular hip, knee, and ankle extensor muscles. The correlation coefficients for biarticular muscles were low. The model results showed that active state of gastrocnemius was high during increase of origin-to-insertion length (LOI), whereas active state of soleus was low during the start of increase of LOI and rose to a plateau at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a compromise between minimizing energy dissipation and using the stretch-shortening cycle optimally. Furthermore, it was found that the net plantar flexion moment during running reached a value of 302 Nm, which was 158% and 127% higher than the peak values reached in maximal jump and sprint push-offs, respectively. It was argued that the higher mechanical output in running than in jumping could be ascribed to the utilization of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.
Biomechanics of sprint running. A review.
Sports Med. 1992 Jun;13(6):376-92. Review.
Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.
Activity of mono- and biarticular leg muscles during sprint running.
Eur J Appl Physiol Occup Physiol. 1985;54(5):524-32.
A cinematographic recording of the movements of the lower limbs together with simultaneous emg tracings from nine lower limb muscles were obtained from two male track sprinters during three phases of a 100 m sprint run. The extensor muscles of the hip joint were found to be the primary movers by acceleration of the body's center of gravity (C.G.) during the ground phase of the running cycle. The extensors of the knee joint were also important in this, but to a minor extent, while the plantar flexors of the ankle joint showed the least contribution. The biarticular muscles functioned in a way different from the monoarticular muscles in the sense that they perform eccentric work during the flight and recovery phases and concentric work during the whole ground phase (support), whereas the monoarticular muscles are restricted first to eccentric work and then to concentric work during the ground phase. Furthermore, the biarticular muscles show variation (and rate of variation) in muscle length to a larger extent than the monoarticular muscles. Paradoxical muscle actions appear to take place around the knee joint, where the hamstring muscles, m. gastrocnemius, m. vastus laterialis and m. vastus medialis act as synergists by extending the knee joint during the last part of the ground phase.
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