Another muscle of the rotator cuff, the subscapularis is a large, triangle-shaped muscle that arises from the large anterior subscapular fossa. It passes laterally into both the lesser tubercle of the humerus and the anterior portion of the shoulder joint capsule.
Innervated (controlled) by the upper and lower subscapular nerves, this muscle modulates the deltoid’s movement, adducting and medially rotating the humerus’ head. In cases where the arm is raised, the subscapularis pulls the humerus forward and downward. The muscle also provides protection for the shoulder joint, minimizing the likelihood of humerus head displacement.