Infraspinatus fatigue during resisted arm elevation with isometric contraction: an electromyographic study

Abstract

Various forms of resistance are used in rotator cuff training programs. However, the muscular activity of the infraspinatus during arm elevation has not been clarified in detail. We aimed to evaluate infraspinatus fatigue during resisted arm elevation in various positions. The dominant (right) shoulders of 39 healthy subjects were examined. Average mean power frequency shifts of the infraspinatus and deltoid were evaluated electromyographically when the subjects performed isometric contractions equivalent to 30% of the maximal voluntary isometric contraction force for 60 s during 90° arm elevation in the sagittal and scapular planes, prone and side-lying external rotations, and repeated side-lying external rotation exercise. Further, the arm-elevation force was measured before and after the repeated external rotation exercise. Analysis of variance and paired t tests were used for statistical analyses; differences at P < .05 were considered significant. The infraspinatus was fatigued easily during resisted arm elevation in the sagittal plane compared with the scapular plane (P < .01). Comparisons of sagittal-plane elevation with side-lying and prone external rotations revealed no significant differences in the fatigue levels. The arm-elevation force after the repeated external rotations was significantly decreased in the sagittal plane compared with the scapular plane (P < .01). In clinical settings, this data may be helpful in knowing how to helpful to protect the infraspinatus after surgical repair. Therefore, therapeutic exercise regimes with resisted arm elevation should avoid infraspinatus overfatigue in the sagittal plane in the early postoperative period.