EACH BODY SEGMENT FUNCTION DURING THE SUPPORT PHASE OF THE DROP JUMP

Abstract

INTRODUCTION: The purpose of this study was to investigate each body segment function in the takeoff motion of the drop jump. Ten male athletes performed a drop jump with the height of 40cm. They were instructed to use arm action. Their takeoff motions were filmed at 20OHz with a high speed camera. Two-dimensional coordinates were obtained by digitizing the motion with a sampling frequency of 20OHz. The data was filtered with a Butterworth digital filter at 8.5Hz. BSP of Chandler et al. (1975) were used to estimate the segmental centers of gravity and the mass center of the whole body. This data were used to calculate the generated momenta of the arms trunk (head and trunk), takeoff legs, thighs, shanks and feet in the vertical direction using method of Ae et al. (1985). Accelerative forces were calculated generated momenta by numerical differentiation. RESULTS: The arms showed a positive (but small) accelerative force (accelerating the body upward) in the early half of the support phase, and a small negative force (checking the body downward) in the later half. The trunk showed a negative accelerative force immediately after the touchdown, then gave a twopeaked pattern of positive force in the midpoint of phase and a negative force in the phase immediately before the takeoff. The takeoff legs showed the positive accelerative force throughout the overall takeoff phase, which is especially large immediately after the touchdown and before the takeoff. The force of the takeoff legs was larger than that of other parts. The thighs showed a negative accelerative force immediately after touchdown, then gave a two-peaked pattern of positive one in the midpoint of phase, and the negative one. The thighs showed the same pattern as the trunk. The shanks gave both positive and negative force alternately during takeoff. The feet showed the positive accelerative force throughout the overall takeoff phase, having the larger one immediately after the touchdown and before the takeoff. CONCLUSIONS: The arms are charged with the function of accelerating the body upward in the early half of the support phase. The trunk takes the charge of accelerating around the midpoint of phase. The takeoff legs have the accelerating function throughout the overall takeoff phase. The thighs are charged with the function around the midpoint, the shanks in the phase immediately after the touchdown and before the takeoff, and the feet during the overall takeoff phase. The positive force of the feet is especially large in the phase immediately after the touchdown and before the takeoff, which accelerate the body upward.