Electromyographic Analysis of Shoulder Muscles During Common Rehabilitation Exercises

Reinold MM, Wilk KE, Flesig GS, Zheng N, Barrentine SW, Chmielewski T, Cody RC, Jameson GG, Andrews JR. Electromyographic analysis of the rotator cuff and deltoid musculature during common shoulder external rotation exercise. Journal of Orthopedic Sports Physical Therapy 34(7):385-94, 2004

Reinold MM, Macrina LC, Wilk KE, Fleisig GS, Dun S, Barrentine SW, Ellerbusch MT, Andrews JR. Electromyographic analysis of the supraspinatus and deltoid muscles during 3 common rehabilitation exercises. J Athl Training 42(4):464-469, 2007.

Two studies were conducted to quantify electromyographic (EMG) muscle activity of the infraspinatus, teres minor, supraspinatus, posterior deltoid, and middle deltoid during exercises commonly used to strengthen the shoulder external rotators.

Methods

EMG measured using intramuscular electrodes were analyzed in healthy subjects during 9 shoulder exercises: prone horizontal abduction at 100 degrees of abduction and full external rotation (ER), prone ER at 90 degrees of abduction, standing ER at 90 degrees of abduction, standing ER in the scapular plane (45 degrees abduction, 30 degrees horizontal adduction), standing ER at 0 degrees of abduction, standing ER at degrees of abduction with a towel roll, and sidelying ER at 0 degrees of abduction, standing elevations in the scapular plane ("full can"), and standing elevation in the scapular plane with glenohumeral internal rotation ("empty can"). The peak percentage of maximal voluntary isometric contraction (MVIC) for muscle was compared among exercises using a 1-way repeated measures analysis of variance (P<0.05).

Results

In the first study, EMG was compared among all exercises except empty can and full can. Sidelying ER produced the greatest amount of EMG activity for the infraspinatus (62% MVIC) and teres minor (67% MVIC). The greatest amount of activity of the supraspinatus (82% MVIC), middle deltoid (87% MVIC), and posterior deltoid (88%) was observed during prone horizontal abduction at 100 degrees with full ER.

In a comparison of prone horizontal abduction at 100 degrees of abduction and full external rotation (ER), empty can, and full can, there were no significant differences in supraspinatus activity. However, the activity levels of the deltoid muscles were altered based on the exercise. The full can approach had the least activity of the three exercises for deltoid muscles; therefore, this may be the best method to strengthen the supraspinatus muscle. The empty can exercise appears to be the best method to employ the middle deltoid muscle, while the full can approach most fully employs the posterior deltoid muscle.