ABSTRACT
This study examined variations in shoulder loading due to differences in the site of stepping foot contact during baseball pitching, while comparing flat ground and mound conditions. Measurement was performed, involving 10 right-handed pitchers who belonged to university baseball clubs, under original flat ground and mound conditions. Pitching movements were classified into 3 categories: [normal], [narrow], and [outside]. Through 3-dimensional motion analysis using a motion capture system, the following results were obtained: 1. The pitching velocity was significantly higher in the [normal] compared with [narrow] and [outside] conditions and under the mound compared with flat ground condition. 2. The peak torque of the shoulder internal rotation was markedly lower in the [narrow] compared with [normal] condition. There were no significant differences between the [normal] and [outside] conditions or between the flat ground and mound conditions. 3. The posterior, superior, and inferior shearing forces, as well as the proximal traction force, which influence the humeral head of the shoulder, were markedly greater in the [normal] compared with [narrow] and [outside] conditions. The anterior and posterior shearing forces and proximal traction force were significantly greater under the mound compared with flat ground conditions. Based on the results, the internal rotation torque of the shoulder, as well as the shearing and traction forces influencing the humeral head of the shoulder, may vary due to differences in the site of stepping foot contact during baseball pitching and between flat ground and mound conditions. The former may also be useful to prevent pitching-related shoulder injuries.