OPTIMAL NORMALIZATION TESTS FOR SHOULDER MUSCLE ACTIVATION - AN ELECTROMYOGRAPHIC STUDY

To accurately compare electromyographic data from different muscles an d different subjects, it is necessary to normalize the integrated data obtained from each muscle. The purpose of this study was to identify the manual muscle testing positions that elicit maximal neural activat ion (integrated electromyography) of three rotator cuff muscles (supra spinatus. infraspinatus, and subscapularis) and five shoulder synergis ts (pectoralis major, latissimus dorsi, and anterior, middle, and post erior deltoids). The electromyographic activity of these eight muscles was examined in the nondominant shoulders of nine subjects. Indwellin g wire electrodes (supraspinatus, infraspinatus, and subscapularis) an d surface adhesive electrodes (pectoralis major, latissimus dorsi, and anterior. middle, and posterior deltoids) were placed. Each subject p erformed a series of 27 isometric contractions. and optimal tests (max imal neural activation) were identified for each muscle. Four tests we re identified that resulted in the maximal neural activation of all ei ght shoulder muscles: 90 degrees of scapular elevation with -45 degree s of humeral rotation for the supraspinatus, anterior deltoid, and mid dle deltoid; external rotation at 90 degrees of scapular elevation and -45 degrees of humeral rotation for the infraspinatus and posterior d eltoid; internal rotation at 90 degrees of scapular elevation and neut ral humeral rotation for the subscapularis and latissimus dorsi; and i nternal rotation at 0 degrees of elevation and neutral rotation for th e pectoralis major. These results identify four standard testing posit ions that will provide reference values for normalization of maximal v oluntary contraction for the eight muscles of the shoulder examined in this study. Standardization of these test positions offers normalizat ion guidelines that can be used in future dynamic electromyography stu dies of the shoulder.