The shoulder is one of the most versatile parts of the body, and allows us to do basically every activity that requires moving one or both arms. The shoulder joint has the largest range of motion of all the joints in the human body, thanks to a team of many muscles and tendons working together to stabilize it. In this article, you’ll learn about the anatomy of the shoulder muscles which makes all of this possible.
Muscles of the shoulder and their functions
The ball-and-socket joint of the shoulder might be the most mobile, but that comes with a cost: lack of stability. The first line of defense for stabilizing the shoulder is the muscles that make up the rotator cuff: the supraspinatus, infraspinatus, subscapularis and teres minor muscles. These four muscles rotate, abduct and adduct the upper arm, while their tendons support and stabilize the joint.
There are several other muscles around the rotator cuff which allow the shoulder to move in various directions. The largest of these, the deltoid, which is located on top of the shoulder joint, helps to abduct the arms (raising them out to the sides). A group of muscles on the anterior face of the joint, the coracobrachilalis, serratus anterior, and the pectoralis major and minor, are responsible for flexion/adduction of the arms toward each other in front (towards the chest).
Two other muscles on the posterior face, the latissimus dorsi and teres major, have a similar function but adducting the arms towards each other behind the body (as when holding your hands together behind your back). Finally, the trapezius, rhomboid major and levator scapulae muscles of the pectoral girdle and back are responsible for lifting the shoulders in a “shrugging” motion.
Delicacy of the rotator cuff and shoulder joint
The shoulder joint is very vulnerable to injury from repetitive or sudden stress, as many amateur tennis players can surely attest to. This is especially true when the surrounding muscles are not strong enough to properly stabilize the joint. This is why it’s dangerous to swing or yank young children by the arms – this type of stress can cause serious damage to the joint, including tearing of the tendons of the rotator cuff and dislocation of the shoulder.