Muscles play a vital role in giving the shoulder both mobility and stability. The muscles that control the shoulder originate at the scapula and thoracic cage, and attach to the humerus and scapula by tendons.
Tendons are part of the muscle, whose function is to attach muscle to bone. Like the instruments in an orchestra, the interaction of joints and muscles in the shoulder is complex – with each component playing an important role in overall function. If there is restriction or weakness in any one of the structures of the shoulder, it can set up a cycle of pain and dysfunction.
In the shoulder, there are muscles that move the arm, muscles that stabilize the arm, and some muscles that do both. The rotator cuff muscles are a group of four muscles (supraspinatous, infraspinatous, teres major and subscapularis) that originate in the scapular region and attach to the humerus. Their function is to move the shoulder while stabilizing the humerus in the glenoid fossa. Each of the muscles of the rotator cuff has a specific job to do, while they work together to ensure normal shoulder function.
Other movers in the shoulder include the deltoid, pectoralis major, teres minor and the long head of the biceps.
Important shoulder stabilizers are the rhomboids, serratus anterior, trapezius, and levator scapular.