It may be concluded that both peripheral and central mechanisms may operate in the pathophysiology of both impaired muscle function and pain in FM. These mechanisms may in part be attributable to physical deconditioning and disuse of muscle secondary to the characteristic pain and fatigue so often seen in FM. Most likely the initiation of this condition is multifactorial and the combination of peripheral and central factors that constitute a vicious circle may perpetuate the condition into a chronic state.