Simulation of Human Jumping - T Ask Alteration

INTRODUCTION The performance of maximal effort human jumping is an important aspect of many sporting skills. Some have used descriptive models to explain the segmental coordination pattern used by elite jumpers (Bobbert et al., 1988), while others have turned to forward dynamics models in which the kinematics of jumping are simulated (Pandy et al., 1991; van Soest et al., 1992). One interesting class of simulations are optimization models, in which the kinetic and kinematic profiles that generate an optimal movement outcome are predicted by optimizing an objective function associated with successful completion of the motion. Vertical jumping studies have become popular in part because the objective function is unambiguous the desired outcome is maximal jump height. In addition, optimal control models using 'bang-bang' control are relevant due to the maximal effort nature of these jumps (Pandy et al., 1991). Underlying these optimization studies is a basic question of interest to move­ ment scientists: How does the CNS coordinate the multi-segmented musculoskeletal system to successfully complete a motion? Jensen et al. (1991) examined segmental kinematics in maximal effort jumping under different task conditions in an attempt to describe features inherent in successful jumping. Subjects jumped at varying take-off angles, ranging from a vertical jump to a standing long jump (forward; horizontal). Using the timing of leg joint reversals as descriptive markers, a general proximal-to-distal coordination pattern was shown. The present investigation was undertaken to extend the scope of this 'task analysis' through optimization models. As a first step in this modeling scheme we constructed a simple model with extensor joint torque actuators. In this paper we report the basic coordination associated with different jumping tasks by examining the pattern of joint torque onset times.