External mechanical work done during the acceleration stage of maximal sprint running and its association with...

This study aimed to elucidate how external mechanical work done during maximal acceleration sprint running changes with increasing running velocity and is associated with running performance. In twelve young males, work done at each step over 50 m from the start was calculated from mechanical energy changes in horizontal anterior-posterior and vertical directions and was divided into braking (-W_kap and -W_v, respectively) and propulsive (+W_kap and +W_v, respectively) phases. The maximal running velocity (V_max) appeared at 35.87±7.76 m and the time required to run 50 m (T_{50 m}) was 7.11±0.54 s. At 80% V_max or higher, +W_kap largely decreased and -W_kap abruptly increased. The change in the difference between +W_kap and |-W_kap| (ΔW_kap) at every step was relatively small at 70% V_max or lower. Total work done over 50 m was 82.4±7.5 J kg^-1 for +W_kap, 36.2±4.4 J kg^-1 for |-W_kap|, 14.3±1.9 J kg^-1 for +W_v, and 10.4±1.2 J kg^-1 for |-W_v|. The total ΔW_kap over 50 m was more strongly correlated with T_50 m (r=-0.946, P<0.0001) than the corresponding associations for the other work variables. These results indicate that in maximal sprint running over 50 m, work done during the propulsive phase in the horizontal anterior-posterior direction accounts for the majority of the total external work done during the acceleration stage, and maximizing it while suppressing work done during the braking phase is essential to achieve a high running performance.