Studies on maximal voluntary muscle contraction in patients with fibromyalgia.

In view of clinical experience of a low-force output in testing situations in patients with fibromyalgia syndrome (FS), this study evaluated the possibility of reaching a higher muscular performance by use of superimposed electrical stimulation: the tests mainly involved knee-extension in a Kin Com dynamometer. Twenty-five patients fulfilling the criteria of FS were compared with 22 healthy subjects. The patients showed a markedly reduced maximal voluntary contraction, but superimposed electrical stimulation revealed submaximal values. The electromyographic activity during stool climbing exceeded that recorded during maximum voluntary contraction during the dynamometric test. The cause of the reduced voluntary maximal performance is discussed. An impaired control mechanism at a supraspinal level is suggested. This has to be considered when measuring muscle strength in FS patients. Tests related to functional activities are recommended as measures of muscular performance in this patient group.