In 20 healthy, young adult male subjects, the muscular activity of the upper, middle and
lower trapezius and the lower digitations of the serratus anterior were studied
electromyographically during arm abduction in the plane of the scapula. The patterns of
electrical activity of the trapezius and lower serratus anterior muscles were observed to
increase progressively during abduction of the arm; however, a plateau phase was
demonstrated in all four of the muscle parts studied. Despite the presence of considerable …