The objectives of this study were to (1) investigate the effect of the timing of the upper body joint motions in baseball batting on the bat-head speed and (2) develop and evaluate a simulation model inputting the individual hand forces on the bat. Twenty-three male collegiate baseball players performed tee batting set at waist height. A 10-segment angle-driven simulation model consisting of a bat and upper body was driven using the coordinate data of the standard motion. Performance optimization was conducted by changing the timing of the joint angle time histories of the upper body to increase the maximum bat-head speed. The optimization simultaneously estimated the individual hand forces by polynomial approximation dependent on the total bat forces to assess joint torques of the upper body. The bat-head speed increased to 39.2 m/s from 35.6 m/s, and the optimized timings were characterized by the earlier timing of the barrel-side elbow supination, wrist radial flexion, torso right lateral flexion, and the later timing of the barrel-side shoulder abduction. It is concluded that the skillful coordination of the individual joint movements for the upper body can produce a higher bat-head speed through effective sequencing of proximal to distal movements.
Keywords: angle-driven; change in timing; computer simulation; standard motion.