Muscular strength relationship between normal grade manual muscle testing and isokinetic measurement of the shoulder internal and external rotators

Abstract

The measurement of muscular strength of the shoulder internal and external rotators is an integral part of the comprehensive evaluation and treatment of the shoulder joint. The purpose of this study was to compare normal grade (S /S) manual muscle strength with isokinetic testing of the shoulder internal and external rotators. One hundred and fourteen consecutive subjects were tested isokinetically in the supine position with 90° of glenohumeral joint abduction on a Cybex 3S0 dynamometer. Prior to isokinetic testing each patient was tested by two physical therapists using manual muscle testing (MMT) with the shoulder abducted 90° for internal OR) and external (ER) rotation. All subjects were rated as normal (S /S) grade for both IR and ER by both therapists to be included in this investigation. A two factor analysis of variance was used to test for differences between extremities. Results of this study showed significant (P < 0.01) differences between extremities in isokinetic peak torque and single repetition work scores. Differences between extremities ranged from 11 to 28% among a sample with normal grade (MMT). The results of this study identify objective, isokinetically measured discrepancies in muscular strength in subjects rated as 'normal' in shoulder internal and external rotation strength. This study demonstrates the efficacy of isokinetic testing of the shoulder internal and external rotators in clinical rehabilitation and evaluation of the glenohumeral joint.