Diminished central activation during maximal voluntary contraction in chronic fatigue syndrome.
OBJECTIVE
We have investigated whether central activation failure (CAF) is increased during local muscle fatigue in chronic fatigue syndrome (CFS).


METHODS
Fourteen female CFS patients and 14 age-matched healthy female controls made a 2 min sustained maximal voluntary contraction (MVC) of the biceps brachii muscle. Before, during, and after sustained MVC, electrical endplate stimulation was applied. Force and 5 channel surface EMG (sEMG) were registered.


RESULTS
Although force responses upon stimulation during rest did not differ between patients and controls, MVC was significantly lower in patients. Already at the beginning of sustained MVC, CFS patients showed significantly larger CAF than controls (36.5+/-17.0% and 12.9+/-13.3%, respectively). For all individual patients mean CAF over the first 45 s was higher than 30%, while it was below 30% for all controls. Less peripheral fatigue in patients was demonstrated by the changes in muscle fibre conduction velocity and the differences between force responses before and after contraction.


CONCLUSIONS
Central activation is diminished in CFS patients. Possible causes include changed perception, impaired concentration, reduced effort and physiologically defined changes, e.g. in the corticospinal excitability or the concentration of neurotransmitters. As a consequence, demands on the muscle are lower, resulting in less peripheral fatigue.


CONCLUSIONS
CFS patients show reduced central activation during MVC. The underlying pathophysiological processes remain still to be determined.
Department of Clinical Neurophysiology, University Medical Centre Nijmegen, Internal postal code 314, P.O. Box 9101, 6500 HB Nijmegen, Netherlands.
M L
ML
Schillings
J S
JS
Kalkman
S P
SP
van der Werf
B G M
BG
van Engelen
G
G
Bleijenberg
M J
MJ
Zwarts
D000328:Adult; D001132:Arm; D016022:Case-Control Studies; D004576:Electromyography; D015673:Fatigue Syndrome, Chronic / Q000503:physiopathology*; D005260:Female; D006801:Humans; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009431:Neural Conduction; D013997:Time Factors