A SIMULATION STUDY OF VERTICAL JUMPING FROM DIFFERENT STARTING POSTURES

This paper addresses the question of whether maximal vertical jump hei ght depends on initial jumping posture. A direct dynamics computer sim ulation approach was used to avoid subject preference and practice eff ects. The human body was modeled as four rigid segments connected by i deal hinge joints, with movement constrained to the sagittal plane and driven by three single-joint torque actuators. Maximal height jumps w ere found for each of 125 different intial postures. For each initial posture, the optimal pattern of joint torque actuator onset times was found using a multidimensional simplex algorithm searching for maximal jump height. The model results revealed that maximal jump height is r elatively insensitive io initial posture, but that the pattern of join t torque onset times necessary to effect these optimal heights varies considerably. Model kinematics indicate that the variability in onset times is necessary to allow the body to re-orient itself in different ways during the downward countermovement phase. This variable re-orien tation strategy is followed by a more stereotyped upward thrust phase that is similar despite the differences in starting postures. Model ce nter of mass, joint and segmental kinematics show many features found in experimental studies of jumping, despite the exclusive use of singl e joint torque actuators. However, a proximal-to-distal sequence of jo int coordination was not found, possibly because of the omission of an tagonist and bi-articular muscles. The results suggest that similar ve rtical jump heights should be obtained using a wide range of initial s tarting positions. Copyright (C) 1996 Published by Elsevier Science Lt d.