Shoulder Joint Muscles
The shoulder joint consists of the clavicle, scapula and humerus (upper arm bone). Due to the nature of the joint there is a huge range of movement or shoulder joint actions available. The muscles of the shoulder joint are the subscapularis, latissimus dorsi, infraspinatus, teres minor, teres major, supraspinatus, deltoid and pectoralis major (pec muscles).
The subscapularis muscle is one of the four rotator cuff muscles. It is hidden behind the rip cage on the underside of the scapula or shoulder blade and is often injured by throwing sports.
The Latissimus dorsi muscle is one of the largest in the body. It is a powerful extensor muscle of the arm and is used extensively in chinning and climbing. They are commonly known at the lats.
The Infraspinatus muscle is one of the four rotator cuff muscles crossing the shoulder joint and is commonly injured. It is the main external rotator of the shoulder joint.
Teres Minor is one of the four rotator cuff muscles surrounding the shoulder. Its main action, along with Infraspinatus is to externally rotate the shoulder joint. There are two Teres muscles, the other being Teres Major.
Teres major is only functional when the Rhomboids fix the scapula. This muscle mainly helps Latissimus dorsi.
The Supraspinatus muscle is one of the four muscles which make up the rotator cuff. Its main function is to stabilise the upper arm by holding the head of the humerus in position. It is important in throwing motions to control any forward motion of the head of humerus.
The deltoid muscle is used in all side lifting movements and any movement of the humerus on the scapula. It is divided into three portions, anterior, middle and posterior, with the fibres having different roles due to their orientation.
Pectoralis major is the largest and most superficial of the two chest muscles. Pec major and the anterior fibres of Deltoid work closely together. Pec-fly and push-up exercises work the Pectoralis major.