Effect of Glenohumeral Internal Rotation Deficit on Shoulder in Baseball Pitchers during Fastball

Adaptations to the pitching shoulder, including increased external rotation (ER), bony adaptation, and humeral head retroversion, seem to be the norm and needed for success. We have learned to measure the total arc of rotation, and we understand if ER is increased, then; as a result, the internal rotation (IR) will be decreased. I have heard many debates on managing Glenohumeral Internal Rotation Deficit (GIRD). However, I see more of a need to strengthen the shoulder and scapular muscles. I also believe that stretching external rotation is beneficial as well. Below is a brief explanation of this study.

The purpose of this study was to investigate whether baseball pitchers with GIRD change their pitching mechanism. A three-dimensional motion analysis system (Eagle System, Motion Analysis Corporation, Santa Rosa, CA, USA) was used to capture the pitching motion while performing fastball pitches. The kinematics and kinetics of the throwing shoulder and trunk were analyzed based on motion captured data. At the instant of ball release, the GIRD group showed lower shoulder external rotation and trunk rotation, and larger shoulder horizontal adduction. In addition, the GIRD group exhibited a significantly larger shoulder inferior force in the cocking and acceleration phase, and a significantly larger internal rotation torque in the acceleration phase. The present results suggested that pitchers with GIRD need stretch training to enlarge a joint range of motion and improve trunk strength and flexibility to alleviate potential problems associated with pitching in GIRD pitchers.

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