The rotator cuff is a group of four muscles that attach the scapula (shoulder blade) to the humerus (upper arm bone). They provide stability to the shoulder joint, especially during overhead rotational movements, such as throwing a ball or swimming. While these muscles act as a group to stabilize the shoulder, they also each have a specific function.
Supraspinatus
The supraspinatus runs from the part of the shoulder blade nearest the neck to the top of the humerus. Its main function is to abduct, or to move your arm away from your body.
Infraspinatus
The infraspinatus goes from the long border of the scapula that's nearest your spine and comes together to attach to the top back part of your humerus. It functions to externally rotate, or turn your upper arm toward the back of your body.
Teres Minor
The teres minor is a much smaller muscle that lies just below the infraspinatus. It also helps externally rotate your arm.
Subscapularis
The subscapularis is the only rotator cuff muscle that lies on the inside of your scapula, next to your ribs. It is positioned to internally rotate, or turn your upper arm toward the front of your body.
