Evaluation of isokinetic force production and associated muscle activity in the scapular rotators during a protraction-retraction movement in overhead athletes with impingement symptoms

Objectives: To determine if the muscle force and electromyographic activity in the scapular rotators of overhead athletes with impingement symptoms showed differences between the injured and non-injured sides. Methods: Isokinetic peak force was evaluated during protraction and retraction of the shoulder girdle, with simultaneous recording of electromyographic activity of the three trapezius muscles and the serratus anterior muscle, in 19 overhead athletes with impingement symptoms. Results: Paired t tests showed significantly lower peak force during isokinetic protraction at high velocity (p< 0.05), a significantly lower protraction/ retraction ratio (p< 0.01), and significantly lower electromyographic activity in the lower trapezius muscle during isokinetic retraction on the injured side than on the non-injured side (p< 0.05). Conclusion: These results confirm that patients with impingement symptoms show abnormal muscle performance at the scapulothoracic joint.