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.
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.
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.
Teres major is only functional when the Rhomboids fix the scapula. This muscle mainly helps Latissimus dorsi.
The Triceps Brachii also assists Latissimus Dorsi in extending the shoulder joint. It contracts strongly during the up phase of a push up, to straighten the arm.
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.