Movement · Shoulders

Scapular upward rotation

The shoulder blade turning on the ribcage so that the socket ends up facing upward — the motion that lets the arm get overhead. Upper trapezius lifts the outer end, lower trapezius pulls the inner-lower corner down, and serratus anterior swings the blade around the ribs; the three form a force couple, so the blade rotates rather than shrugs. Good looks like: the blade turning smoothly and staying flat on the ribs, with about one degree of blade rotation for every two of arm movement. When it fails, the arm runs out of room and the tissues under the acromion get squeezed — the mechanism behind most overhead shoulder pain.