Firing rate and conduction velocity of single motor units in the trapezius muscle in Fibromyalgia patients and healthy controls

Journal: Journal of Electromyography Kinesiology. 2007 Apr 23; [E-publication ahead of print]

Authors and affiliations: Gerdle B, Ostlund N, Gronlund C, Roeleveld K, Karlsson JS. Department of Rehabilitation Medicine, Faculty of Health Sciences, and Pain and Rehabilitation Centre, University Hospital, Linkoping, Sweden.

PMID: 17459728

Fibromyalgia is a common chronic pain condition in the population (2-4%), which often is associated with prominent negative consequences with respect to participation in daily activities. There are several reports in the literature concerning the effects of acute experimental pain on motor control. However, a more heterogeneous picture exists in the literature with respect to whether chronic pain conditions affect motor control.

This study compares firing rate and conduction velocity (CV) of single motor units (MUs) in the trapezius muscle of Fibromyalgia patients (FM) and healthy controls (CON). Multi-channel surface electromyography was used to estimate both MU firing rate and CV because this technique allows simultaneous estimation of both these variables and the measurements are easy and non-invasive.

In this study, 29 FM and 30 CON subjects participated and performed isometric shoulder elevations using weights up to 4kg. No significant differences in the firing rate of MUs in the trapezius muscle were found between the FM and CON groups (95% confidence interval was -1.9 and 1.3 pulses per second). There were no significant differences in CV between the groups at 1 and 2kg load. However, the FM group had significantly higher CV in contractions without external load (p=0.004).

We were unable to confirm the pain-adaptation model since no differences in firing rate between the two groups were found. CV was significantly higher in FM than in healthy controls; this might be due to alterations in histopathology and microcirculation.

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