The presence of abnormalities in fibromyalgia muscle using current methodological approaches is well established. The more serious abnormalities are demonstrated by histologic studies particularly on electron microscopy: disorganisation of Z bands and abnormalities in the number and shape of mitochondria. Biochemical studies and P 31 magnetic resonance spectroscopy show inconstant abnormalities of ATP and phosphocreatine levels. Mitochondrial abnormalities reduced capillary circulation and thickened capillary endothelium may result in decreased availability of oxygen and impaired oxidative phosphorylation as well as ATP synthesis. These abnormalities do not seem to be the consequences of the much-discussed deconditioning of muscles although these consequences are not well known. Further studies of energy metabolism of the muscle during exercise are needed.