To investigate whether patients with fibromyalgia (FM) have normal motor unit recruitment in relation to muscle metabolism during exhausting exercise and recovery, and whether the reduced voluntary muscle force normally seen is related to a smaller muscle size.
Female patients with FM and sedentary controls were examined using simultaneous 31P nuclear magnetic resonance spectroscopy (NMR) and surface electromyography (SEMG) during exhaustive static exercise of the anterior tibial muscle and during recovery. The maximum voluntary contraction force was estimated, and the maximum cross sectional muscle area was evaluated using 1H NMR imaging. The sedentary controls were matched to patients for sex, age and, as far as possible, daily physical activity levels.
Patients with FM had reduced maximum voluntary contraction force in relation to the sedentary controls, despite having similar muscle size. In general the myoelectrical-metabolic relation during exercise and recovery was normal in patients with FM.
The less extreme changes in motor unit recruitment and metabolism during exhaustive exercise indicated a lower exercise tolerance that could be connected with the lower physical activity levels.