Correlation of throwing mechanics with elbow valgus load in adult baseball pitchers

Arnel L Aguinaldo, Henry Chambers
American Journal of Sports Medicine 2009, 37 (10): 2043-8

BACKGROUND: Studies have shown that various biomechanical factors affect valgus extension overload during baseball pitching; yet, their relationships are not clearly defined, and factors such as trunk rotation and arm slot have not been investigated.

HYPOTHESIS: The onset of trunk rotation, with other biomechanical variables that define sequential body motion, will significantly predict elbow valgus loading.

STUDY DESIGN: Descriptive laboratory study.

METHODS: Sixty-nine adult baseball players pitched off an indoor mound during 3-dimensional motion analysis to measure whole body kinematics and kinetics at 240 Hz. Thirteen biomechanical variables were calculated and extracted for regression analysis to investigate their associations with elbow valgus load. A 2-way analysis of variance compared valgus torques between pitchers with 2 onsets of trunk rotation (before and after front-foot contact) and 2 arm slot positions (overhand and sidearm).

RESULTS: Six biomechanical variables had significant correlations (P < .02) with elbow valgus torque-with maximum shoulder external rotation, elbow flexion at peak valgus torque, and elbow valgus loading rate accounting for 68% of its variance. Reduced elbow valgus torques were associated with increased elbow flexion (P < .01). Players who initiated trunk rotation before front-foot contact had significantly higher elbow valgus torques than did those who rotated afterward (P = .02). Fourteen pitchers displayed a sidearm delivery and had significantly higher elbow valgus torques than did those with an overhand arm slot position.

CONCLUSION: Valgus torque at the elbow during baseball pitching is associated with 6 biomechanical variables of sequential body motion. A condition of late trunk rotation, reduced shoulder external rotation, and increased elbow flexion appeared to be most closely related to valgus torque. Sidearm pitchers appeared to be more susceptible than overhand pitchers to reduced elbow valgus torque.

CLINICAL RELEVANCE: The biomechanical findings of this study offer scientific feedback for developing methods used to minimize the effects of valgus load on pitching-related elbow injuries.

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