We have observed the pattern of muscle action during rotational movement of the humerus by recording angular deviation and electromyograph simultaneously.
Results were summarrized as follow:
1) From the beginning of external rotation of the humerus, electrical activity was recorded from the infraspinatus and the teres minor.
During later half of this movement, electrical activity was found from the deltoideus (posterior fiber), the latissimus dorsi, the supraspinatus and the rhomboideus.
2) In internal rotation of the humerus, electrical activity was recorded from the subscapularis. The pectralis major was active in half of the cases, but the deltoideus (anterior fiber) and the latissimus dorsi were inactive during this movement.
