BACKGROUND: The developing musculoskeletal system of a youth pitcher is substantially different from that of the adult professional pitcher, predisposing the younger players to a different set of injuries.

METHODS: High-speed videography of 39 professional and 13 youth pitchers were obtained. High-speed motion analysis was performed to calculate average anterior forces and arm positions at maximal force generation.

RESULTS: Professional players generated an average of 33.8+/-14.4 N/kg maximal anterior force, corresponding to 151.9+/-17.0 degrees of external rotation. Youth pitchers generated 16.2+/-3.8 N/kg of anterior forces, corresponding to 118.0+/-23.4 degrees of external rotation. The degree of coronal abduction and horizontal abduction between the 2 groups were not significantly different-92.4+/-9.0 degrees in professionals versus 91.7+/-7.9 degrees in the youth and 11.1+/-11.1 degrees of horizontal abduction in professionals versus 7.8+/-14.1 degrees in the younger throwers. Professional pitchers exerted higher internal rotation torque at 19.4+/-4.1 Nm/kg versus 5.6+/-1.0 Nm/kg in youth, and compressive forces were found to be 121.7+/-21.7 N/kg in professional pitchers compared with 47.5+/-7.6 N/kg in the youth pitchers.

CONCLUSIONS: Youth pitchers experience significant anterior shoulder forces and internal rotation torques, although these are lower than professional pitchers.

CLINICAL RELEVANCE: Overhead throwing as a youth can lead to shoulder injuries and can predispose the shoulder to more significant injuries as an adult pitcher.