Muscle Monday - Rotator Cuff Muscles
The rotator cuff is a group of four deep muscles that hold your upper arm in place in your shoulder. These muscles support you to make all the motions of your arm and shoulder. The head of your humerus (your upper arm bone) [2] fits into the socket of your scapula (shoulder blade) [1]. When you extend your arm out away from your body, the rotator cuff muscles keep it from popping out of the socket.
You can use the acronym SITS to help remember these four muscles:
Supraspinatus [3] is responsible for about the first 15 degrees of abduction motion (movement away from the centerline of your body). After that, your deltoid and trapezius muscles take over.
Infraspinatus [4] is the main muscle responsible for lateral rotation of your arm away from the centerline of your body. It’s a thick triangular muscle. It covers the back of your shoulder blade deep below the skin and close to the bone.
Teres minor [5] is a small, narrow muscle on the back of your shoulder blade just below the infraspinatus that also contributes to lateral (external) rotation of your arm.
Subscapularis[6] is a large triangular-shaped muscle that lies below the other three. It’s the strongest, largest, and most used of the four rotator cuff muscles. It participates in most shoulder motions but is especially important for rotation of your arm toward the midline of your body (medial rotation). Unlike the other three muscles, the subscapularis attaches to the front, not the back, of your upper arm.
Each of these four muscles attaches to the upper part of your humerus at a different point. From top to bottom, their order is the same as the acronym:
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
Rotator cuff injuries are very common, especially in people over 40, athletes, and people whose work involves repeatedly lifting their arms overhead. Stay tuned for more on rotator cuff injuries in a future post!
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