Comparison of the electromyographic activity in the upper trapezius and biceps brachii muscle in subjects with muscular disorders: a pilot study
- 265 Downloads
The aim of the present study was to investigate the extent to which work-related muscular disorders of the upper trapezius affect the activity of other pain-free muscles, in particular in the biceps brachii. Two groups of female subjects (age >43 years) participated in the study: seven affected subjects with self-reported disorders in the shoulder/neck region (cases) and nine healthy subjects (control group). Multi-channel electromyography (EMG) and force were recorded during maximum voluntary contractions (MVC) and during 6 min sustained contractions (at 30% MVC) of the upper trapezius and biceps brachii on the dominant side. From the EMG signals, the root mean square (RMS), median frequency (MDF) and single motor unit (MU) conduction velocity (CV) were estimated. From the force signal, the coefficient of variation was calculated. All data are presented as mean values and standard deviation. Differences between the cases and controls were found in the MVC force of the upper trapezius, which was lower in cases [253 (70) N] than in controls [357 (75) N], while the coefficient of variation of force during the sustained contraction was increased [cases 5.5 (2.2); controls 4.1 (1.9)]. The RMS (normalized to the RMS at MVC) during the 6 min sustained contractions was significantly lower in the cases than in the controls for both the upper trapezius and the biceps brachii. A tendency towards a smaller increase in the RMS with fatigue was only found in the trapezius muscle [slope: cases 6.5 (14.1) %/min, controls 10.2 (12.9) %/min]. No differences were found between the two subject groups with respect to the MDF and single MU CV in both muscles. While the lower RMS for the trapezius muscles of the cases may reflect changes at the local level, as well as in motor control, the lower biceps activity indicates a change in the central control strategies of the primarily unaffected muscle. Indications for a changed fatigability of the muscle were only found in the trapezius.
KeywordsBiceps brachii Fatigue Isometric contraction Surface electromyography Trapezius myalgia
This work has been supported by the European Shared Cost Project ‘Neuromuscular Assessment of Elderly Workers’ (NEW) (QLRT-2000–00139).
- Basmajian J, DeLuca CJ (1985) Muscle alive: their function revealed by electromyography. Williams and Wilkins, BaltimoreGoogle Scholar
- Hägg GM (1991) Static work loads and occupational myalgia—a new explanation model. In: PA Anderson (ed) Electromyographical kinesiology, Excerpta Medica, Amsterdam, pp 141–144Google 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
- Juul-Kristensen B, Kadefors R, Hansen K, Byström P, Sandsjö L, Sjøgaard G (2004) Clinical signs and physical function in neck and upper extremities among elderly female computer users: the NEW study. Eur J Appl Physiol DOI 10.1007/s00421-004-1220-4Google 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
- Sjøgaard G, Søgaard K, Hermens HJ, Sandsjö L, Läubli T, Thorn S, Vollenbroek-Hutton MMR, Sell L, Christensen H, Klipstein A, Kadefors R, Merletti R (2005) Neuromuscular assessment in Elderly Workers from four EU countries with and without work related musculoskeletal disorders. The NEW-study design and physiological findings. Eur J Appl Physiol (in press)Google Scholar