Windmill pitching produces high forces and torques at the shoulder and elbow, making the biceps labrum complex susceptible to overuse injury. Little is known about the muscle firing patterns during a windmill pitch. Hypothesis Biceps muscle activity is greater during a windmill pitch than during an overhand throw. Study Design Descriptive laboratory study. Methods Seven female windmill pitchers underwent motion analysis and surface electromyography evaluation of their biceps muscles during windmill and overhand throwing. Marker motion analysis, muscle activity, and ball release were captured simultaneously. Surface electromyography trials were collected and related to the athletes` phases of pitching and throwing, identified based on predefined softball and baseball pitching mechanics. Results Throws were of similar velocity (24 m/s, 53 mph, P = .71), but peak biceps brachii muscle activation during the windmill pitch was significantly greater than during the overhand throw when normalized (38% vs 19% manual muscle test, P = .02). The highest muscle activity occurred at the 9-o`clock phase of the windmill pitch, during which the biceps brachii undergoes eccentric contraction. In the overhand throw, the highest level of biceps activity occurred during arm cocking. Conclusion In female athletes, biceps brachii activity during the windmill pitch is higher than during an overhand throw and is most active during the 9-o`clock and follow-through phases of the pitch. Clinical Relevance Repetitive eccentric biceps contractions may help explain the high incidence of anterior shoulder pain clinically observed in elite windmill pitchers. Injury prevention and treatment mechanisms should focus on the phases with the highest muscle activity.
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