Upper trapezius muscle conduction velocity during fatigue in subjects with and without work-related muscular disorders: a non-invasive high spatial resolution approach
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The development of fatigue at the muscle fibre level can be assessed in terms of a decrease in conduction velocity (CV). The present study aimed to investigate if work-related muscular disorders in occupations characterised by static loads of long duration affect fatigue resistance in the painful muscle. A group of eight secretaries suffering from bilateral chronic muscle pain in the shoulder/neck region was compared to a group of healthy subjects. The upper trapezius muscle was studied under isometric contractions, holding the arm in the horizontal plane up to the endurance point. Changes in CV estimated at the motor unit level were investigated using a non-invasive high spatial resolution electromyographic (EMG) approach. In addition, the number of motor unit potentials per second (PPS), and the root mean square (RMS) of bipolar signals were assessed, and the results reported as the mean and standard error for each value. Subjects with work-related disorders showed less pronounced changes in CV with respect to healthy subjects. No differences between subjects with and without work-related disorders were encountered for the PPS and RMS. The present findings on CV indicate an increased fatigue-related recruitment of MUs in the painful muscle with respect to a healthy muscle. The fact that this recruitment is not reflected in the PPS and RMS estimates might be due to a fatigue-induced decrease in the firing rate and/or the de-recruitment of fatigued MUs. Furthermore, methodological limitations of the adopted method in the estimation of ‘global’ parameters such as the PPS and RMS have to be considered.
KeywordsConduction velocity Fatigue Motor unit Myalgia Surface electromyography
This work has been supported by the European Shared Cost Project ‘Neuromuscular Assessment of Elderly Workers’ (NEW) (QLRT-2000-00139).
- Bigland-Ritchie BR, Dawson NJ, Johansson RS, Lippold OC (1986) Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary contractions. J Physiol (Lond) 379:451–459Google Scholar
- Hägg GM (1991) Static work loads and occupational myalgia—a new explanation model. In: Anderson PA, Hobart DJ, Danoff JV (eds) Electromyographical kinesiology. Elsevier, Amsterdam, pp141–143Google Scholar
- Hermens HJ, Freriks B (1997) The state of the art on sensors and sensor placement procedures for surface electromyography: a proposal for sensor placement procedures. Report of the SENIAM Project, Roessingh Research and Development, EnschedeGoogle Scholar
- Öberg T, Sandsjö L, Kadefors R, Larsson SE (1992) Electromyographic changes in work-related myalgia of the trapezius muscle. Eur J Appl Physiol 65:251–257Google Scholar
- Spitzer W, Leblanc F, Dupuis M (1987) Scientific approach to the assessment and management of activity-related spinal disorders: a monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine12 [Suppl]:1–59Google Scholar