The Biomechanics of Throwing

The shoulder is a complex joint that affords the most degrees of freedom of any joint in the body. As such, there are several static and dynamic structures that act on the shoulder with every shoulder motion to maintain the humeral head in proper position. The overhead athlete, specifically the baseball pitcher, faces a multitude of forces about the shoulder with each athletic encounter. These forces can often lead to chronic, attritional injuries that manifest as decreases in both velocity and accuracy over several months, or less frequently, as acute, traumatic injuries. To understand how to manage the different pathology that arises in the shoulder of the overhead athlete, it is first imperative to understand the biomechanical forces that act on the athlete׳s shoulder with varying shoulder motions, specifically the baseball pitch. The baseball pitch, commonly divided into 6 distinct phases, is a classic example of the shoulder forces experienced by an overhead athlete, and serves as a basis for understanding shoulder biomechanics in these players. Football quarterbacks, javelin throwers, swimmers, and other athletes also experience similar significant forces about the shoulder. With a complete understanding of shoulder kinetics and kinematics in the overhead athlete, one can improve diagnostic accuracy and treatment of subtle pathologies seen in this patient population.