EMG ANALYSIS OF SHOULDER POSITIONING IN TESTING AND STRENGTHENING THESUPRASPINATUS

We examined the electromyographic (EMG) activity of the supraspinatus and other rotator cuff muscles, the three portions of the deltoid musc le, and the pectoralis major muscle in two previously suggested positi ons for isolating the supraspinatus. The position suggested by Jobe an d colleagues is with the elbow extended, the shoulder in full internal rotation, and the arm in the scapular plane. Blackburn and colleagues recommended the prone position, with the elbow extended and the arm a bducted to 100 degrees and externally rotated. Fine-wire EMG activity was obtained from the rotator cuff muscles and surface EMG from the ot her muscles in 17 subjects tested in these two positions. Both positio ns resulted in significant activity of the supraspinatus, but the diff erence between these two positions was not statistically significant. The Jobe position produced greater activation of the anterior deltoid and pectoralis major, whereas the Blackburn position caused greater ac tivation of the posterior deltoid. Both positions produced significant activation of the middle deltoid. We conclude that either position ca n be used to strengthen the supraspinatus; however, neither position s electively isolates the supraspinatus during manual muscle testing.