The shoulder joint, also known as the glenohumeral joint is a ball and socket joint and consists of the humerus (upper arm bone), clavicle (collar bone) and scapula (shoulder blade). The muscles which stabilize and enable movement of the joint are the pectoralis major, teres major, supraspinatus, deltoid and latissimus dorsi.
Teres major is only a functional shoulder muscle when the Rhomboids fix the scapula. This muscle mainly helps the latissimus dorsi.
Pectoralis major is the largest and most superficial of the two chest muscles. The pec major and the anterior fibers of Deltoid work closely together. Pec fly and push-up exercises work the Pectoralis major.
The deltoid muscle is one of the best known shoulder muscles, it is used in all side lifting movements and any movement of the humerus on the scapula. It is divided into two portions, anterior and posterior, with the fibres having different roles due to their orientation.
Subscapularis is one of the four rotator cuff muscles. The muscle also acts to hold the head of the humerus in position and prevents it from moving forward.
The Supraspinatus muscle is one of the four muscles which make up the rotator cuff. Its main function is to stabilise the humerus by holding the head of the humerus in position.
The Infraspinatus muscle is one of the four rotator cuff muscles and is commonly injured. It is the main external rotator of the shoulder joint and works in conjunction with the Terres Minor.
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.
Teres Minor is one of the four rotator cuff muscles. Its main action, along with Infraspinatus is to externally rotate the shoulder joint. There are two Teres muscles, the other being Teres Major.