Fibromyalgia: Increased reactivity of the muscle membrane and a role of central regulation

•Muscle fiber conduction in fibromyalgia is precipitated by changed membrane physiology.•Muscle membrane conduction speed in fibromyalgia rises excessively when adopting a limb position.•The muscle membrane in fibromyalgia is probably hyperactive due to deregulation from higher systems. Fibromyalgia (FM) is characterized by widespread muscle pain and central neural deregulation. Previous studies showed increased muscle fiber conduction velocity (CV) in non-painful muscles of FM patients. This study investigates the relationship between central activation and the CV in FM. Twenty-two females with primary FM and 21 controls underwent surface electromyography of the non-painful biceps brachii. Mean CVs were calculated from the motor unit potential velocities (CV-MUPs), and the CV-MUPs’ statistical distributions were presented as histograms. The amount of muscle activity (average rectified voltage, ARV) was measured. The CV was higher in the FM-group than in the controls (P = 0.021), with CV-MUPs generally shifted to higher values, indicative of increased muscle membrane propagation speeds. The largest increase in the CV of the FM-group occurred when adopting and maintaining a limb position at only 5% of maximum strength (P