EMG biofeedback effectiveness to alter muscle activity pattern and scapular kinematics in subjects with and without shoulder impingement

Background: Muscle imbalance between serratus anterior (SA), upper trapezius (UA), middle trapezius (MT), and lower trapezius (LT) muscles has been observed in subjects with subacromial impingement syndrome (SAIS). Objective: (1) To investigate the effect of electromyography (EMG) biofeedback training on muscle balance ratios and scapular kinematics in healthy adults and subjects with SAIS. (2) To investigate whether the effects of EMG biofeedback on muscle balance ratios are different between groups. Design: Twelve healthy adults and 13 subjects with SAIS were recruited in this study. EMG was used to record the activity of scapular muscles. The ratios (UT/SA, UT/MT, and UT/LT) during exercises with/without EMG biofeedback were calculated. Scapular kinematics were recorded before and after exercises with/without EMG biofeedback. Results: For the subjects with SAIS, muscle balance ratios were lower during forward flexion with EMG biofeedback than during exercise only (UT/SA: 70.3-45.2; UT/LT: 124.8-94.6). Additionally, similar results were found during side-lying external rotation (UT/MT: 58.5-36.4). For the scapular upward rotation and tipping in both groups, there were no significant differences with and without EMG biofeedback. Conclusion: EMG biofeedback improved the scapular muscular balance during training exercises in both groups. Further clinical trials should investigate the long-term effects of EMG biofeedback.