Muscle · Shoulders

Lower trapezius

Pars ascendens musculi trapezii

The lower trapezius is the long, flat, triangular lower portion of the muscle, running up from the mid- and lower thoracic spine to the inner end of the shoulder blade's ridge. It pulls the shoulder blade down and back, and — with the upper trapezius and serratus anterior as a force couple — it rotates the socket of the shoulder blade upward so the arm can clear the way overhead. It is thin, easy to miss, and easy to substitute for. Momentum's tight-vs-weak chart lists it as one of the classically weak upper-body muscles, and its shoulder-pain flow names it directly as the muscle to activate; scapular upward-rotation failure is the movement failure that system attributes to shoulder pain. This is an activation muscle, not a release muscle.