Muscle · Shoulders

Infraspinatus

Musculus infraspinatus

The broad muscle filling the hollow below the ridge of the shoulder blade, and the shoulder's principal external rotator — the muscle that turns the arm outward so the palm can face forward, and the one that decelerates the arm at the end of a throw. It also pulls down on the head of the arm bone during elevation, which is what keeps the top of the humerus from crowding the bony roof above it. Because it is covered by nothing but thin fascia and skin over most of its surface it is one of the easiest deep muscles to actually feel, and one of the most commonly tender in anyone who works or trains with their arms overhead.