Low EMG-EMG Coherence Across Shoulder Muscles During Fatigue Correlates With Pain In Rotator Cuff Disease

Rotator cuff disease (RCD) is one of the most prevalent causes of functional limitation, accounting for 85% of all shoulder pain cases. It is associated with altered neuromuscular control across the rotator cuff and deltoid muscles, which can affect joint stability and cause pain. Electromyographic (EMG)-EMG coherence is a measure of shared oscillatory input between the electrical signals of two muscles, reflecting a common neural drive. PURPOSE: We investigated the correlation between shoulder pain levels and intermuscular EMG coherence across the rotator cuff and deltoid muscles. METHODS: Surface EMG was recorded from the infraspinatus (IS) and middle deltoid (MD). Intramuscular EMG was recorded from supraspinatus (SS). Thirty-two adults with RCD performed an isometric fatiguing contraction at 30° scaption at 25% maximal voluntary contraction. Pain levels were self-reported before and immediately after the fatigue task using a visual analog scale (VAS) from 0 to 10. Pearson correlation analysis was used to determine the correlation between changes in pain levels and Z-transformed pooled intermuscular coherence across three muscle pairs (SS-IS, SS-MD, IS-MD) before and after the fatigue task. RESULTS: There was a significant negative correlation between the increase in pain with fatigue (1.69 ± 0.35) and the increase in SS-IS coherence (0.003 ± 0.002) in the beta-band (r = - 0.498, p = 0.02). There was no significant correlation between pain levels and intermuscular coherence in the SS-MD (-0.008 ± 0.01, p = 0.58) or IS-MD (-0.002 ± 0.004, p = 0.3) in the beta-band. In the delta-band, there was no significant correlation between pain levels (2.4 ± 0.44) and the coherence for any of the three muscle pairs (SS-IS, 0.004 ± 0.007, p = 0.7; SS-MD, 0.002 ± 0.003, p = 0.87; IS-MD, 0.005 ± 0.005, p = 0.65). CONCLUSION: The findings demonstrate that increases in pain levels are associated with decreases in beta-band coherence between the SS and IS muscles, suggesting that the deficiency in common drive to the rotator cuff muscles causes pain. Future studies should investigate therapeutic interventions that enhance coherence in beta-band, with the goal of mitigating pain and restoring the neuromuscular control patterns in RCD.