Optimal normalization tests for shoulder muscle activation: An electromyographic study

Abstract

To accurately compare electromyographic data from different muscles and 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 activation (integrated electromyography) of three rotator cuff muscles (supraspinatus, infraspinatus, and subscapularis) and five shoulder synergists (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids). The electromyographic activity of these eight muscles was examined in the nondominant shoulders of nine subjects. Indwelling wire electrodes (supraspinatus, infraspinatus, and subscapularis) and surface adhesive electrodes (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids) were placed. Each subject performed a series of 27 isometric contractions, and optimal tests (maximal neural activation) were identified for each muscle. Four tests were identified that resulted in the maximal neural activation of all eight shoulder muscles: 90 degrees of scapular elevation with -45 degrees of humeral rotation for the supraspinatus, anterior deltoid, and middle deltoid: external rotation at 90 degrees of scapular elevation and -45 degrees of humeral rotation for the infraspinatus and posterior deltoid: internal rotation at 90 degrees of scapular elevation and neutral humeral rotation for the subscapularis and latissimus dorsi: and internal rotation at 0 degree of elevation and neutral rotation for the pectoralis major. These results identify four standard testing positions that will provide reference values for normalization of maximal voluntary contraction for the eight muscles of the shoulder examined in this study. Standardization of these test positions offers normalization guidelines that can be used in future dynamic electromyography studies of the shoulder.

Standard maximum isometric voluntary contraction tests for normalizing shoulder muscle EMG

“…Three of the four suggested Shoulder Normalization Tests were previously described by these authors. Our results support those of Kelly et al 2 for the ''empty can'' test, finding it maximally activated supraspinatus, anterior deltoid, and middle deltoid, and the ''internal rotation 908'' test which maximally activated subscapularis (upper and lower parts in the current study) and latissimus dorsi. Our results differed from Kelly et al 2 in that the ''empty can'' test was better able to maximally activate the posterior deltoid than the ''external rotation at 908'' abduction identified by these authors.…”

“…Our results support those of Kelly et al 2 for the ''empty can'' test, finding it maximally activated supraspinatus, anterior deltoid, and middle deltoid, and the ''internal rotation 908'' test which maximally activated subscapularis (upper and lower parts in the current study) and latissimus dorsi. Our results differed from Kelly et al 2 in that the ''empty can'' test was better able to maximally activate the posterior deltoid than the ''external rotation at 908'' abduction identified by these authors. Furthermore, Kelly et al 2 did not examine the ''palm press'' test and concluded that internal rotation at 08 abduction was the most effective test for pectoralis major.…”

“…Our results corroborate the work of Kelly et al 2 and Ekstrom et al 3 to identify standard shoulder muscle MVIC test procedures. Three of the four suggested Shoulder Normalization Tests were previously described by these authors.…”

“…Kelly et al 2 and Ekstrom et al 3 have begun the process toward establishing standard MVIC tests for shoulder EMG normalization. However, no EMG study has simultaneously examined rotator cuff, axio/ scapulohumeral, and scapulothoracic muscles during MVICs.…”

Effect of velocity on shoulder muscle recruitment patterns during wheelchair propulsion in nondisabled individuals: Pilot study

“…A total of four muscle tests were performed following the methods described by Boettcher et al [22] and Kelly et al [23]. The test order was block randomized.…”