Early research suggested that FM is basically a muscular disorder. One relatively recent study reported that FM patients had lower levels of the muscle-cell enzyme phosphocreatine and adenosine triphosphate (ATP). Such enzymes regulate the ebb and flow of calcium in muscle cells, an important component in their ability to contract and relax. If ATP levels are low, calcium is not “pushed back” into the cells and the muscle remains contracted. Such abnormal enzyme levels could derive from signals in the brain, although some researchers have observed overly thickened capillaries in the muscle tissue of FM patients, which could produce lower enzymes levels as well as reduce the flow of oxygen-rich in the muscle tissue. Nevertheless, most research is now showing that FM is probably due to abnormalities in nervous or immune systems rather than in muscles.