Overhead throwing creates a variety of challenges for baseball players, especially pitchers. Due to the biomechanical consequences of repetitive throwing, pitchers are at increased risk for a variety of shoulder and elbow injuries such as shoulder impingement, labral tears, and ulnar collateral ligament tears. These injuries can often lead to long periods of recovery and, in some cases, surgery.
One of the biomechanical changes that pitchers undergo is a loss of internal (or forward rotation) rotation in their shoulder joint. With repetitive cocking of the shoulder backward, pitchers develop tightness in an area of the back of the shoulder joint called the posterior capsule. This tightness leads to a decrease in the internal rotation of the throwing shoulder as compared to the non-throwing shoulder as seen in the images below. This is called Glenohumeral Internal Rotation Deficit or GIRD. GIRD has been shown to be a risk factor for SLAP labral tears and UCL ligament tears. Both injuries typically require surgery and recovery time of 12-18 months.