What is the function of the subscapularis muscle related to the glenohumeral joint?

The subscapularis muscle plays a crucial role in the movement of the glenohumeral joint, primarily responsible for the internal rotation of the shoulder. It is one of the four muscles that comprise the rotator cuff, located on the anterior aspect of the scapula. When the subscapularis contracts, it pulls the head of the humerus inward and downward, which contributes significantly to stabilizing the shoulder joint while allowing for internal rotation.

Understanding the mechanics of shoulder movement, the internal rotation facilitated by the subscapularis is vital for various functional activities. This internal rotation is essential during actions such as throwing a ball or performing a butterfly stroke in swimming, where the shoulder needs to rotate inward.

This muscle's function is distinctly associated with internal rotation, differentiating it from other shoulder movements that involve external rotation, abduction, or adduction, which are primarily governed by other muscles surrounding the shoulder. Therefore, the primary responsibility of the subscapularis in relation to the glenohumeral joint is to facilitate internal rotation.