Corticomotor excitability and perception of effort during sustained exercise in the chronic fatigue syndrome

Objective: We have investigated the possibility of a central basis for the complaints of fatigue and poor exercise tolerance in subjects with chronic fatigue syndrome (CFS). Methods: Transcranial magnetic stimulation of the motor cortex was used to measure sequential changes in motor evoked potential (MEP) amplitude, post-excitatory silent period (SP) duration and twitch force of the biceps brachii muscle during a 20% maximum isometric elbow flexor contraction maintained to the point of exhaustion. Ten patients with post-infectious CFS and 10 age- and sex-matched control subjects were studied. Results were analysed using non-parametric repeated measures analysis of variance (Friedmanʹs test) and Mann–Whitney U-tests for intra- and inter-group comparisons respectively. Results: Mean endurance time for the CFS group was lower (13.1±3.2 min, mean±SEM) than controls (18.6±2.6 min, P<0.05) and CFS subjects reported higher ratings of perceived exertion. During the exercise period MEP amplitude and SP duration increased in both groups but to a lesser extent in CFS subjects. Interpolated twitch force amplitude also increased during exercise, being more pronounced in CFS subjects. Conclusion: The findings are in keeping with an exercise-related diminution in central motor drive in association with an increased perception of effort in CFS