Muscle fibre characteristics & lactate responses to exercise in Chronic Fatigue Syndrome (CFS)

OBJECTIVES: To examine the proportions of type 1 and type 2

muscle fibres and the degree of muscle fibre atrophy and

hypertrophy in patients with chronic fatigue syndrome in

relation to lactate responses to exercise, and to determine to

what extent any abnormalities found might be due to

inactivity. METHODS: Quadriceps needle muscle biopsies were

obtained from 105 patients with chronic fatigue syndrome and

the proportions of type 1 and 2 fibres and fibre atrophy and

hypertrophy factors were determined from histochemical

preparations, using a semiautomated image analysis system.

Forty one randomly selected biopsies were also examined by

electron microscopy. Lactate responses to exercise were

measured in the subanaerobic threshold exercise test (SATET).

RESULTS: Inactivity would be expected to result in a shift to

type 2 fibre predominance and fibre atrophy, but type 1

predominance (23%) was more common than type 2 predominance

(3%), and fibre atrophy was found in only 10.4% of cases.

Patients with increased lactate responses to exercise did have

significantly fewer type 1 muscle fibres (p<0.043 males,

p<0.0003 females), but there was no evidence that this group

was less active than the patients with normal lactate

responses. No significant ultrastructural abnormalities were

found. CONCLUSION: Muscle histometry in patients with chronic

fatigue syndrome generally did not show the changes expected

as a result of inactivity. However, patients with abnormal

lactate responses to exercise had a significantly lower

proportion of mitochondria rich type 1 muscle fibres.

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