The movement of the upper arm and shoulder is controlled by a group of four muscles that make up the rotator cuff. The largest and strongest muscle in this group is the subscapularis muscle. This triangle shaped muscle begins in the scapula, located on the underside of the shoulder blade, and extends up to the humerus, located on the front of the upper arm. The function of the muscle is to stabilize and rotate the shoulder joint to allow the arm to turn inward. When the arm is extended, it draws the humerus forward and downward. It also prevents the dislocation of the head of the humerus. The major arteries that run through the subscapularis muscle are the cervical artery and the subscapular artery. The subscapularis muscle is innervated by the lower and upper subscapular nerves. The subscapularis muscle is the most-used muscle in the shoulder. It is the primary muscle used in pitching, hitting, swimming, and all racquet sports. As a result, injuries to the shoulder muscle are common among athletes.