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 < 0.001),  whereas that of the controls increased only slightly and non-significantly, and  that of the FM-group did not increase at all. In the CFS-group, the number of  MUPs conveying very high conduction velocities increased abundantly with force  and the MUPs narrowed. CONCLUSION: Our results suggest disturbed muscle membrane  function in CFS patients, in their motor units involved in low force generation.  Central neural deregulation may contribute to this disturbance. SIGNIFICANCE:  These findings help to detangle the underlying mechanisms of CFS.