What is the primary function of the subscapularis muscle?

The primary function of the subscapularis muscle is internal rotation of the shoulder. This muscle is one of the four rotator cuff muscles and is located on the anterior aspect of the scapula. When the subscapularis contracts, it pulls the humerus toward the body's midline, thereby rotating the arm inward. This action is crucial for various movements and stability within the shoulder joint, especially during activities that require the arm to be rotated toward the body.

Understanding the subscapularis’s role helps highlight its importance in maintaining shoulder function, especially in athletic activities and overhead motions, where internal rotation is a significant component. This muscle’s action is contrasted with that of other shoulder muscles, which may facilitate different movements such as abduction, extension, or external rotation, but these are not the primary functions of the subscapularis.