Chronic fatigue syndrome: Abnormally fast muscle fiber conduction in the membranes of motor units at low static force load.

Abstract Objective Chronic fatigue syndrome (CFS) and fibromyalgia (FM) are disorders of unknown etiology and unclear pathophysiology, with overlapping symptoms of – especially muscular –fatigue and pain. Studies have shown increased muscle fiber conduction velocity (CV) in the non-painful muscles of FM patients. We investigated whether CFS patients also show CV abnormalities. Methods Females with CFS (n=25), with FM (n=22), and healthy controls (n=21) underwent surface electromyography of the biceps brachii, loaded up to 20% of maximum strength, during short static contractions. The mean CV and motor unit potential (MUP) velocities with their statistical distribution were measured. Results The CV changes with force differed between CFS-group and both FM-group and controls (P=0.01). The CV of the CFS-group increased excessively with force (P Conclusion Our results suggest disturbed membrane function in CFS patients, in their motor units involved in low force generation. Central neural deregulation may contribute to these findings. Significance These findings help to detangle the underlying mechanisms of CFS.