Electromyography and Nerve Conduction Velocity for the Evaluation of the Infraspinatus Muscle and the Suprascapular Nerve in Professional Beach Volleyball Players

Background: Beach volleyball is an overhead sport with a high prevalence of infraspinatus muscle atrophy of the hitting shoulder. Hypothesis: Infraspinatus muscle atrophy seems to be caused by a repetitive traction injury of the suprascapular nerve. Early pathological findings might be assessed with surface electromyography (EMG) and nerve conduction velocity (NCV) measurements. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Fully competitive professional beach volleyball players were assessed with a structured interview, shoulder examination, strength measurements (external rotation and elevation), and neurophysiological examination (surface EMG and NCV of the infraspinatus and supraspinatus muscles and the suprascapular nerve, respectively) during the Beach Volleyball Grand Slam tournament 2010 in Klagenfurt, Austria. Results: Thirty-five men with an average age of 28 years were examined. Visible infraspinatus atrophy was found in 12 players (34%), of which 8 (23%) had slight atrophy and 4 (11%) had severe atrophy. External rotation (90%; P < .006) and elevation strength (93%; P = .03) were significantly lower in the hitting shoulder. Electromyography revealed a higher activation pattern in the infraspinatus muscle of the hitting arm in players with no or slight atrophy (P = .001) but a significantly lower activation pattern in players with severe atrophy (P = .013). Nerve conduction velocity measurements showed a significant higher latency and lower amplitude in the hitting shoulder of the total study group and the subgroup with infraspinatus atrophy. Conclusion: Professional beach volleyball players have a high frequency of infraspinatus atrophy (34%) and significantly reduced shoulder strength of the hitting shoulder. These findings are not associated with demographic factors. Electromyography and NCV measurements suggest a suprascapular nerve involvement caused by repetitive strain injuries of the nerve. External rotation strength measurements and NCV measurements can detect a side-to-side difference early, while EMG may show compensation mechanisms for progressive damaging of the suprascapular nerve and, as a result, loss of infraspinatus muscle strength.