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 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.
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 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.