During which movement is the subscapularis muscle primarily active?

The subscapularis muscle plays a crucial role in the internal rotation of the shoulder. As one of the four rotator cuff muscles, it is located on the anterior surface of the scapula and is primarily responsible for rotating the humerus inward toward the body. When the arm is brought across the torso or positioned in a way that emphasizes internal rotation, the subscapularis is significantly activated to facilitate and stabilize this movement.

In contrast, abduction and external rotation involve opposing muscle actions, primarily utilizing muscles like the supraspinatus and infraspinatus, respectively. Similarly, while the subscapularis contributes to shoulder extension, its primary function remains focused on internal rotation. Therefore, internal rotation of the shoulder is the specific movement during which the subscapularis muscle is predominantly active.