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Muscle fatigue in early fibromyalgia (FM)

OBJECTIVE. To compare the processes connected with muscle fatigue
during prolonged exercise in patients with fibromyalgia (FM)
with studies of healthy individuals.

METHODS. Nine female
patients with FM, all employed in full or part time, performed
repetitive isometric contractions of the quadriceps muscles at
30% of maximal voluntary contraction (MVC) force in 6 s with 4
s rest between until exhaustion.

electrically stimulated tetanic forces fell continually and
almost in parallel, indicating no central fatigue. The
relaxation rate of the muscle became gradually faster as
previously seen in healthy subjects. Plasma catecholamine
concentrations remained unchanged during the exercise period,
whereas a modest rise in blood lactate and plasma K+ was seen.
The electromyographic (EMG) amplitude recorded during
contractions increased gradually, while no changes were seen
in EMG recorded in resting periods between contractions. Heart
rate and VO2 rose gradually and a small exercise induced pain
was recorded.

CONCLUSION. Our study showed normal
physiological muscle fatigue responses, except for the lack of
increase in plasma catecholamine concentrations during

Mengshoel AM, Saugen E, Forre O, Vollestad NK