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

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 (- and , respectively) and propulsive ( and , respectively) phases. The maximal running velocity () appeared at 35.87±7.76 m and the time required to run 50 m () was 7.11±0.54 s. At 80% or higher, largely decreased and abruptly increased. The change in the difference between and || (Δ) at every step was relatively small at 70% or lower. Total work done over 50 m was 82.4±7.5 J kg for , 36.2±4.4 J kg for ||, 14.3±1.9 J kg for , and 10.4±1.2 J kg for ||. The total Δ over 50 m was more strongly correlated with (=-0.946, <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.