Relationships between run-up speed and external force acting on the center of mass in the running single-leg jump

Abstract

The purpose of this study was to clarify the relationship between the change in direction of the velocity of center of mass (CoM) and the force acting on the center of mass during the take-off phase in a running single-leg jump (RSLJ) with different run-up speed and jumping task. Nine male collegiate jumpers performed RSLJ in two tasks, to jump forward and upward, respectively, with four different run-up speeds. Three-dimensional coordinates of the end positions of the body segments and the ground reaction force (GRF) were obtained using the motion capture system and force platform. The GRF and gravity acting on the CoM were divided into the normal and tangential force relative to the velocity of CoM. The amount of change in direction of CoM velocity was significantly correlated with the normal impulse during take-off phase. As run-up speed or take-off angle increase, the normal impulse and the negative tangential impulse increased in the first phase of take-off. The normal impulse in the second phase was decreased by the shortening of support time in the faster run-up speed. These results suggested that it is important for the change in CoM velocity direction to increase the normal force in the first phase of the take-off and it might be useful for the evaluation of the RSLJ by means of dividing the force into normal and tangential components relative to the velocity.