Shoulder muscle activation and fatigue during a controlled forceful hand grip task

PurposeReliable electromyographic evaluation of the shoulder in common painful conditions is a major challenge due to a reduced range of movement and pain-related muscle inhibition. This study investigates the use of a hand grip task for the assessment of shoulder muscle activation.MethodsMuscle activity and fatigue for supraspinatus and infraspinatus muscles were measured in 16 healthy controls using fine-wire electrodes during a controlled gripping task at 50% of maximum voluntary contraction, in a standardized sitting and arm position. Changes in muscle activity and fatigue were measured by the time-slope of root mean square amplitude and median frequency, respectively.ResultsA significant positive amplitude slope (p < 0.01) was found for both supraspinatus and infraspinatus, indicating that the task resulted in increasing muscle activity. Judging by the median frequency slope, there was no sign of fatigue progression.ConclusionA standardized hand grip task in a neutral position activates key rotator cuff muscles. This might provide a method for electromyographic assessment of shoulder girdle muscles which avoids problems due to pain-related limitation of movement, and might be useful in the development and monitoring of shoulder rehabilitation strategies.