Influence of different initial angles of the trunk segment on the relationship of the body's center of gravity and the joint torque of lower extremity during vertical jumping take-off

Abstract

This study was designed to investigate the relationship of the body's center of gravity (CG) and the joint torque of rhe lower extremities during take-off movement with different initial postures in the jump. Three initial postures were employed: an unconstrained posture (N), posture with head+arms+trunk (HAT) segment perpendicular to the ground (L) and posture with the HAT segment parallel to the ground (T). The experiment consisted of two stages. In the first stage, one subject executed jumps using maximal effort with the three initial postures. Joint torque was calculated by the inverse dynamics approach method. In the second stage, computer simulation was executed by inputting manipulated joint torque amplitude. The kinematics of the CG as calculated in the simulated jumps were compared among N, L, and T postures. In comparison of L and N postures, with the L posture the ratio of work at the knee joint was increased and the knee and ankle joint had no relationship with the horizontal velocity of the CG. The relationship between the knee and ankle joint was highly negative. The increase of ankle joint torque was strongly related to the increase of the vertical velocity of the CG. In comparison of the T and N postures, with the T posture the ratio of work at the knee joint was decreased and the ankle joint demonstrated no relationship with the horizontal velocity of the CG. Other relationships were same as with N. The N posture was more flexible in response to the change of torque amplitude than the other postures.