The muscles that control internal rotation of the shoulder are the pectoralis major, anterior deltoid, latissimus dorsi, teres major, subscapularis, and the muscles of the arm. The pectoralis major is a thick, fan-shaped muscle that extends from the sternum downward toward the upper arm, controlling the internal rotation of the shoulder. The deltoid is a muscle attached to the shoulder, extending from the clavicle to the upper arm, and the anterior bundle of the deltoid can assist the pectoralis major, pulling the arm forward and internally rotating the arm together. The latissimus dorsi not only controls the internal rotation of the shoulder, but also participates in the internal rotation of the arm and the extension of the arm. The subscapularis is a large triangular muscle that fills the space under the scapula. In addition to controlling the internal rotation of the shoulder, it also works with the supraspinatus, infraspinatus, and teres minor to fix the shoulder joint.