Abstract
We used electromyographic analysis to determine the muscle activity of the shoulder muscles during the lift-off test and during resisted internal rotation. The activity in the upper and lower subscapularis muscle during a lift-off test from the region of the midlumbar spine was approximately 70% of maximal voluntary contraction. This level was significantly higher than for all the other muscles tested (P < 0.05). The lift-off test with the hand placed in the region of the midlumbar spine resulted in one-third more electromyographic ac tivity in the subscapularis muscle than when the test was modified and performed with the hand at the but tocks region. A resisted lift-off test resulted in higher activities in all the muscles, but only a small increase in the pectoralis major muscle. The pectoralis major mus cle was significantly more active during resisted inter nal rotation with the arm in front of the body. Compar ison of activity in the upper subscapularis with that in the lower subscapularis muscle showed no significant differences during any of the tests. This study docu ments the importance of the subscapularis muscle dur ing the lift-off test and suggests that other potential internal rotators of the humerus have a limited role in maintaining internal rotation when the arm is placed behind the back.
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