In the motion of shoulder flexion(0-90 degree), the scapula was upward rotated at the center of acromioclaviclular joint. In the abduction, the scapula was upward rotated and depressed with the clavicle elevation and retraction. The purpose of this study is to evaluate the muscle functions around the scapula by electromyographic analysis during the flexion and abduction of the shoulder. EMG activities of upper, middle, and inferior trapezius muscle, and serratus anterior, were examined in 5 static positions from 0 degrees to 150 degrees for 5 seconds in each position during exercises of shoulder flexion and abduction in 6 healthy volunteers. We used Telemyo System 2400(Noraxon USA Inc) and analyzed by MyoVideo and MyoResearch. The relative activity of upper trapezius muscle did not increase, and the muscle activity of serratus anterior was increased significantly during the early phase of flexion. The relative activity of upper, middle trapezius muscle has gradually increased during the early phase of abduction. The scapular upward rotation pattern was different between that in flexion and abduction. This study indicated that the symptom of accessory nerve palsy is disorder of abduction, and the main symptom of long thoracic nerve palsy is the inhibition of shoulder flexion.
