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.
Pectoralis major is the largest and most superficial of the two chest muscles. 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 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.