Effects Of NMES On EMG-EMG Coherence Across Glenohumeral Muscles During Fatigue In Rotator Cuff Disease

Rotator cuff disease (RCD), a common pathology of shoulder pain, can be attributed to muscle weakness and altered humeral head stability, particularly during neuromuscular fatigue. Electromyographic (EMG)-EMG coherence quantifies shared oscillatory input between motoneuron pools, providing insight into motor control deficiencies in RCD. PURPOSE: To investigate the effects of neuromuscular electrical stimulation (NMES) on EMG-EMG coherence across glenohumeral muscles during fatigue in RCD. METHODS: Eight participants with RCD (39 ± 19 yrs) underwent two sessions separated by 72 hrs. Intramuscular EMG was recorded from the supraspinatus (SS), and surface EMG was recorded from the infraspinatus (IS) and middle deltoid (MD) of the painful shoulder. Baseline coherence was recorded for 30s at 25% maximal voluntary contraction (MVC) at 30° scaption before treatment. In session 1, participants received a sham treatment (0 mA) for 10 min. In session 2, NMES was applied at maximal tolerable intensity (30 Hz; 0.2 ms; 4 s-on, 6 s-off) for 10 min. Following each treatment, a sustained isometric 25% MVC task was performed until endurance limit. Z-transformed pooled coherence in the delta (2-5 Hz) and beta (15-35 Hz) bands for SS-IS, SS-MD, and IS-MD pairs were compared across the first and last 30s of fatigue tasks with a 2-way repeated measures ANOVA with Bonferroni post-hoc tests. Change in coherence between sessions was compared using paired t-tests. RESULTS: No significant difference in baseline coherence between sessions. There was a significant increase in SS-IS delta-band coherence with fatigue following NMES (initial: 0.14 ± 0.03, final: 0.20 ± 0.04; p = 0.002), but no significant change following the sham. Beta-band coherence increased with fatigue in both sessions, but to a greater degree in session 2 than in session 1 for both SS-IS (Δsham: 0.02, ΔNMES: 0.07; p = 0.04) and SS-MD (Δsham: 0.02, ΔNMES: 0.08; p = 0.02). No significant difference in IS-MD coherence between sessions. CONCLUSIONS: NMES before a fatiguing task caused an increase in SS-IS and SS-MD coherence, reflecting an excitability effect on the corticospinal tract. NMES enhances coherence across shoulder muscles, potentially improving joint stability and developing neuromuscular rehabilitation strategies for fatigue-related performance declines.