Muscle fiber velocity and electromyographic signs of fatigue in fibromyalgia

INTRODUCTION: Fibromyalgia (FM) is a disorder of widespread muscular pain. We investigated possible differences in surface electromyography (sEMG) in clinically unaffected muscle between patients with FM and controls. METHODS: sEMG was performed on the biceps brachii muscle of 13 women with FM and 14 matched healthy controls during prolonged dynamic exercises, unloaded, and loaded up to 20% of maximum voluntary contraction. The sEMG parameters were: muscle fiber conduction velocity (CV); skewness of motor unit potential (peak) velocities; peak frequency (PF) (number of peaks per second); and average rectified voltage (ARV). RESULTS: There was significantly higher CV in the FM group. Although the FM group performed the tests equally well, their electromyographic fatigue was significantly less expressed compared with controls (in CV, PF, and ARV). CONCLUSION: In the patients with FM, we clearly showed functional abnormalities of the muscle membrane, which led to high conduction velocity and resistance to fatigue in electromyography