Kinetics factors of the lower limb joints decelerating running velocity in the last phase of 100 m race

Abstract

The purpose of the present study was to clarify the factors involved in deceleration in the last phase of a 100 m sprint by comparing the kinetics of the lower limb joints between the maximal running velocity phase (Max) and the deceleration phase (Dec). Five male collegiate sprinters, running 60 m and 100 m at maximal effort, were videotaped with high-speed cameras (250 fps) and the ground reaction force (1000 Hz) was measured at the 50-m and 85-m points. The kinematics and kinetics of the lower limb joints were then calculated. The results were as follows: 1) The deceleration of running velocity was due to a decrease of stride frequency. 2) In the Dec, braking impulse increased, but propulsion impulse decreased significantly. 3) Significant decreases were found in joint torque and negative power exerted by ankle plantar flexors. 4) Hip negative work exerted by hip joint torque in the late support phase tended to decrease, and it is thought that this decrease affected the delay of hip-flex movement during the early recovery phase. These results reveal that the function of the ankle has a direct influence on deceleration, and suggest that the negative work exerted by hip joint torque during the support phase may help to maintain hip-flex movement during the early recovery phase in the final phase of the 100-m sprint.