Background: High internal rotation torque on the shoulder joint during pitching is a major contributor to shoulder injuries. Biomechanical efficiency, which balances ball velocity against normalized joint torque, offers a valuable metric for improving performance and reducing injury. This study aimed to identify kinematic characteristics associated with shoulder internal rotation torque (IRT) biomechanical efficiency in collegiate baseball pitchers. Methods: We analyzed data from 68 male pitchers using multiple regression to assess relationships with 29 kinematic variables. The pitchers were also divided into high- and low-efficiency groups for comparative analysis. Results: Six variables were significantly associated with shoulder IRT efficiency, explaining 41.3% of its variance. Notably, the high-efficiency group exhibited a significantly smaller shoulder abduction angle at stride foot contact (SFC) (83.87 ± 6.7◦ vs. 89.19 ± 8.75◦, p = 0.022) and a significantly larger shoulder external rotation angle at maximum external rotation (MER) (171.3 ± 8.33◦ vs. 165.2 ± 9.50◦, p = 0.027). Conclusions: These results indicate that modifying these specific aspects of pitching mechanics may enhance biomechanical efficiency by reducing the standardized load on the shoulder joint relative to ball velocity, offering practical insights for injury prevention training. However, coaches should note that increasing the angle of shoulder external rotation should be achieved through controlled joint mobility rather than by excessively demanding greater external rotation angles to avoid increasing the risk of injury.
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