ELECTROMYOGRAPHIC ACTIVITY OF SELECTED SHOULDER MUSCLES IN COMMONLY USED THERAPEUTIC EXERCISES

Background and Purpose. The purpose of this study was to evaluate and compare the muscle activity of the supraspinatus, infraspinatus, teres minor and lower trapezius muscles during commonly prescribed therapeu tic exercises in subjects with and without shoulder pathology. Subject s. Twenty healthy subjects (9 male, 11 female) and 20 subjects with re current unilateral shoulder pain and weakness (14 male, 6 female), age d 18 to 40 years (XBAR=28, SD=58), participated in this study Methods. Subjects performed each of the following exercises using a band-held weight: prone lateral (external) rotation, sidelying lateral rotation, and arm elevation in the scapular plane. Indwelling fine-wire electro des recorded electromyographic (EMG) activity during each exercise. Th e EMG activity in five phases of concentric contraction of each exerci se was averaged and divided into three equal time intervals. Mean EMG values normalized to maximal activity for the entire phase of concentr ic contraction and for each of the three intervals were used in subseq uent analyses. Results. Two-way repeated-measures analyses of variance (ANOVAs) revealed between-group differences only in the prone lateral rotation exercise. Compared with subjects without shoulder pathology, subjects with shoulder pain showed significantly greater EMG activity in the infraspinatus muscle and less activity in the supraspinatus mu scle during this exercise. Conclusion and Discussion. These results su ggest that the pattern of muscle activation during specific shoulder m ovements in patients with shoulder pain may be related to pathology. F uture studies are needed to determine whether an imbalance in neuromus cular control is a factor contributing directly to shoulder dysfunctio n or whether such an imbalance is secondary to some pathology.