Corticomotor excitability & perception of effort during sustained exercise in the Chronic Fatigue Syndrome (CFS)

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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 (Friedman’s 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


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.

Sacco P, Hope PA, Thickbroom GW, Byrnes ML, Mastaglia FL

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