Abstract
BackgroundFibromyalgia (FM) is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points in characteristic locations, and the frequent presence of symptoms such as fatigue. The aim of this study was to assess whether the myoelectrical manifestations of fatigue in patients affected by FM are central or peripheral in origin.MethodsEight female patients aged 55.6 ± 13.6 years (FM group) and eight healthy female volunteers aged 50.3 ± 9.3 years (MCG) were studied by means of non-invasive surface electromyography (s-EMG) involving a linear array of 16 electrodes placed on the skin overlying the biceps brachii muscle, with muscle fatigue being evoked by means of voluntary and involuntary (electrically elicited) contractions. Maximal voluntary contractions (MVCs), motor unit action potential conduction velocity distributions (mean ± SD and skewness), and the mean power frequency of the spectrum (MNF) were estimated in order to assess whether there were any significant differences between the two groups and contraction types.ResultsThe motor pattern of recruitment during voluntary contractions was altered in the FM patients, who also showed fewer myoelectrical manifestations of fatigue (normalised conduction velocity rate of changes: -0.074 ± 0.052%/s in FM vs -0.196 ± 0.133%/s in MCG; normalised MNF rate of changes: -0.29 ± 0.16%/s in FM vs -0.66 ± 0.34%/s in MCG). Mean conduction velocity distribution and skewnesses values were higher (p < 0.01) in the FM group. There were no between-group differences in the results obtained from the electrically elicited contractions.ConclusionThe apparent paradox of fewer myoelectrical manifestations of fatigue in FM is the electrophysiological expression of muscle remodelling in terms of the prevalence of slow conducting fatigue-resistant type I fibres. As the only between-group differences concerned voluntary contractions, they are probably more related to central motor control failure than muscle membrane alterations, which suggests pathological muscle fibre remodelling related to altered suprasegmental control.
Highlights
Fibromyalgia (FM) is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points in characteristic locations, and the frequent presence of symptoms such as fatigue
FM is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points at characteristic locations, and the frequent presence of symptoms such as fatigue, poor sleep, irritable bowel symptoms and chronic headache [1,2]
None of the subjects reported any localised biceps brachii muscle pain during the Maximal voluntary contractions (MVCs) or any worsening in FM pain interfering with their ability to perform the requested task, possibly because of the brevity of the required muscle contraction (3 sec)
Summary
Fibromyalgia (FM) is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points in characteristic locations, and the frequent presence of symptoms such as fatigue. FM is characterised by diffuse musculoskeletal pain and stiffness at multiple sites, tender points at characteristic locations, and the frequent presence of symptoms such as fatigue, poor sleep, irritable bowel symptoms and chronic headache [1,2]. The traditional invasive approach is not well tolerated, cannot be frequently repeated, and small bioptic specimens can only provide a limited description of the sampled muscle It leaves a number of open questions concerning the reproducibility of the results and the possibility of inferring the changes induced by treatments
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