Recent evidence has suggested that FM pain can be related to deficits in pain endogenous regulatory control and that novel non-pharmacological interventions, such as tDCS can modulate this system and, consequently, reduce pain intensity. Widespread pain in FM is thought to represent enhanced pain sensitivity that is maintained by central mechanisms. This suggests changes in the descending pain control mechanisms and a possible relationship with the central sensitization phenomenon. Recent evidence has suggested that pain inhibitory pathways are affected in FM; thus, further understanding these pathways' role can significantly change how the treatment of this condition. In this study the investigators will test the effects of two interventions -tDCS and aerobic exercise - on the modulation of the endogenous inhibitory pain system in fibromyalgia.