Voluntary activation deficits of the infraspinatus present as a consequence of pitching-induced fatigue.

Hypothesis: Neuromuscular inhibition of the infraspinatus would be greater and external rotation muscle force would be lower after a simulated game compared with pregame values.

Materials And Methods: The sample included 21 uninjured, asymptomatic high school-aged baseball pitchers. Maximum volitional shoulder external rotation strength was assessed before and after a simulated game with a clinical dynamometer. Voluntary activation of the infraspinatus was assessed during strength testing by a modified burst superimposition technique. Performance-related fatigue was assessed by monitoring pitch velocity, and global fatigue was assessed by subject self-report before and after the game. Statistical testing included paired and independent t tests, with α ≤ .05.

Results: There was no difference between throwing and non-throwing shoulder external rotation strength (P = .12) or voluntary infraspinatus activation (P = .27) before the game. After the game, voluntary activation was significantly lower in the throwing limb compared with pregame activation levels (P = .01). Lower external rotation strength after the game approached statistical significance (P = .06). Pitch velocity was lower in the final inning compared with first-inning velocity (P = .01), and fatigue was significantly greater after the game (P = .01).

Conclusions: Voluntary infraspinatus muscle activation is a mechanism contributing to external rotation muscle weakness in the fatigued pitcher. Understanding mechanisms contributing to muscle weakness is necessary to develop effective injury prevention and rehabilitation programs. Treatment techniques that enhance neuromuscular activation may be a useful strategy for enhancing strength in this population.