Electromyographic analysis of scapular muscles in overhead athletes with rotator cuff tendinopathy - A systematic review

Introduction: Rotator cuff tendinopathy is one of the most common shoulder injuries in overhead athletes. Altered scapular biomechanics have been observed in athletes with rotator cuff tendinopathy; however, the alteration in neuromuscular activity of the scapular muscles is not clear.
Objectives: To conduct a systematic review on the muscle activity pattern assessed by electromyography in overhead athletes with and without rotator cuff tendinopathy.
Method: Electronic database of Embase, PubMed, Web of Science, Scopus, PEDro, and Cochrane were systematically searched from inception to June 2023. Studies that investigated overhead athletes with signs and symptoms suggestive of rotator cuff tendinopathy, and compared the changes in muscle activity pattern of scapular muscles assessed by electromyography were included. Two reviewers independently examined the quality of studies by The Newcastle-Ottawa Scale (NOS) and The Agency for Healthcare Research and Quality (AHRQ).
Results: A total of 12 studies (a total of 479 athletes) were included. The methodological quality was moderate to high (NOS =5-8, AHRQ=9). Our findings showed a consistent pattern of increased EMG activity of the upper trapezius (UT) and decreased EMG activity of the lower trapezius (LT), middle trapezius (MT) and anterior serratus (SA) in overhead athletes with rotator cuff tendinopathy when compared to healthy controls. Besides, athletes with rotator cuff tendinopathy demonstrated a strong trend of increased UT/MT and UT/LT, and earlier onset of UT and delayed onset of the LT and MT and when compared to healthy controls.
Conclusion: Overhead athletes with rotator cuff tendinopathy altered recruitment patterns and muscle activation levels of scapular muscles. Moreover, due to great heterogeneity in the subject selection and study methods, whether alternation in scapular kinematics is associated with changes in the activity pattern of the scapular muscles warrants more high-quality prospective studies.