THE MANUAL MUSCLE EXAMINATION FOR ROTATOR CUFF STRENGTH - AN ELECTROMYOGRAPHIC INVESTIGATION

The electromyographic activity of eight muscles of the rotator cuff an d shoulder girdle (supraspinatus, infraspinatus, subscapularis, pector alis, latissimus dorsi, and the anterior, middle, and posterior deltoi d) was measured from the nondominant shoulders of 11 subjects during a series of 29 isometric contractions. The contractions simulated diffe rent positions used for strength testing of the rotator cuff and invol ved elevation, external rotation, and internal rotation at three degre es of initial humeral rotation (-45 degrees of internal rotation, 0 de grees, +45 degrees of external rotation) and scapular elevation (0 deg rees, 45 degrees, 90 degrees). Isolation of the supraspinatus muscle w as best achieved with the test position of elevation at 90 degrees of scapular elevation and +45 degrees (external rotation) of humeral rota tion. Isolation of the infraspinatus muscle was best achieved with ext ernal rotation at 0 degrees of scapular elevation and -45 degrees (int ernal rotation) of humeral rotation. Isolation of the subscapularis mu scle was best achieved with the Gerber push-off test, This study used four criteria for identifying the optimal manual muscle test for each rotator cuff muscle: 1) maximal activation of the cuff muscle, 2) mini mal contribution from involved shoulder synergists, 3) minimal provoca tion of pain, and 4) good test-retest reliability, Based on the result s of this study and known painful arcs of motion, an objective identif ication of the optimal tests for the manual muscle testing of the cuff was elucidated.