Motor problems are reported by patients with fibromyalgia (FM). However, the mechanisms leading to alterations in motor performance are not well understood. In this study, upper limb position control during sustained isometric contractions was investigated in patients with FM and in healthy controls (HCs).
Fifteen female FM patients and 13 HCs were asked to keep a constant upper limb position during sustained elbow flexion and shoulder abduction, respectively. Subjects received real-time visual feedback on limb position and both tasks were performed unloaded and while supporting loads (1, 2, and 3 kg). Accelerations of the dominant upper limb were recorded, with variance (SD of mean position) and power spectrum analysis used to characterize limb position control. Normalized power of the acceleration signal was extracted for three frequency bands: 1-3 Hz, 4-7 Hz, and 8-12 Hz.
Variance increased with load in both tasks (P < 0.001) but did not differ significantly between patients and HCs (P > 0.17). Power spectrum analysis showed that the FM patients had a higher proportion of normalized power in the 1-3 Hz band, and a lower proportion of normalized power in the 8-12 Hz band compared to HCs (P < 0.05). The results were consistent for all load conditions and for both elbow flexion and shoulder abduction.
FM patients exhibit an altered neuromuscular strategy for upper limb position control compared to HCs. The predominance of low-frequency limb oscillations among FM patients may indicate a sensory deficit.