Interrelationships between different loads in resisted sprints, half-squat 1 RM and kinematic variables in trained...

Resisted sprint running is a common training method for improving sprint-specific strength. It is well-known that an athlete's time to complete a sled-towing sprint increases linearly with increasing sled load. However, to our knowledge, the relationship between the maximum load in sled-towing sprint and the sprint time is unknown, The main purpose of this research was to analyze the relationship between the maximum load in sled-towing sprint, half-squat maximal dynamic strength and the velocity in the acceleration phase in 20-m sprint. A second aim was to compare sprint performance when athletes ran under different conditions: un-resisted and towing sleds. Twenty-one participants (17.86 ± 2.27 years; 1.77 ± 0.06 m and 69.24 ± 7.20 kg) completed a one repetition maximum test (1 RM) from a half-squat position (159.68 ± 22.61 kg) and a series of sled-towing sprints with loads of 0, 5, 10, 15, 20, 25, 30% body mass (Bm) and the maximum resisted sprint load. No significant correlation (P<0.05) was found between half-squat 1 RM and the sprint time in different loaded conditions. Conversely, significant correlations (P<0.05) were found between maximum load in resisted sprint and sprint time (20-m sprint time, r=-0.71; 5% Bm, r=-0.73; 10% Bm, r=-0.53; 15% Bm, r=-0.55; 20% Bm, r=-0.65; 25% Bm, r=-0.44; 30% Bm, r=-0.63; MaxLoad, r= 0.93). The sprinting velocity significantly decreased by 4-22% with all load increases. Stride length (SL) also decreased (17%) significantly across all resisted conditions. In addition, there were significant differences in stride frequency (SF) with loads over 15% Bm. It could be concluded that the knowledge of the individual maximal load in resisted sprint and the effects on the sprinting kinematic with different loads, could be interesting to determinate the optimal load to improve the acceleration phase at sprint running.