Functional subdivision of the upper trapezius muscle during low-level activation

Abstract The electromyographic (EMG) amplitude was recorded using bipolar surface electrodes placed at different positions above the upper trapezius muscle of 16 healthy subjects. One of the aims of this study was to investigate the variation in EMG activity between electrode positions. For this purpose three tasks were performed: a mental activation test, a dynamic movement test and 90° arm abduction. The EMG signals were full-wave rectified and averaged within windows that were 0.2 s in length. Normalized EMG activity showed significantly different EMG amplitudes at different electrode positions for two of the three tasks. The second aim of this study was to investigate whether the upper trapezius muscle may be functionally subdivided. For this purpose the normalized EMG amplitudes of each task were compared with the EMG amplitude recorded during submaximal shoulder elevation. While the EMG level was similar at one electrode position, significant differences were found at some of the other electrode positions, indicating a functional subdivision of the muscle. The present results indicate that for comparisons of upper trapezius EMG activity levels between some tasks or between subjects, it is worthwhile to make EMG recordings at several electrode positions.

[1]  C. Gielen,et al.  The Activation of Motor Units in Coordinated Arm Movements in Humans , 1990 .

[2]  M Hagberg,et al.  Discomfort and load on the upper trapezius muscle when operating a wordprocessor. , 1986, Ergonomics.

[3]  K. Hansen,et al.  Trapezius muscle load as a risk indicator for occupational shoulder-neck complaints , 1993, International archives of occupational and environmental health.

[4]  R H Westgaard,et al.  A case-control study of trapezius muscle activity in office and manual workers with shoulder and neck pain and symptom-free controls , 1995, International archives of occupational and environmental health.

[5]  J. Brown,et al.  An electromyographic analysis of functional differentiation in human pectoralis major muscle. , 1994, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[6]  R H Westgaard,et al.  The effect of motivation on shoulder-muscle tension in attention-demanding tasks. , 1994, Ergonomics.

[7]  E Viikari-Juntura,et al.  Loading of shoulder muscles in a simulated work cycle: comparison between sedentary workers with and without neck-shoulder symptoms. , 1991, Clinical biomechanics.

[8]  W A Weijs,et al.  Electromyographic Heterogeneity in the Human Masseter Muscle , 1992, Journal of dental research.

[9]  B Jonsson,et al.  Measurement and evaluation of local muscular strain in the shoulder during constrained work. , 1982, Journal of human ergology.

[10]  R H Westgaard,et al.  Functional subdivision of the upper trapezius muscle during maximal isometric contractions. , 1995, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.

[11]  R H Westgaard,et al.  Pattern of muscle activity during stereotyped work and its relation to muscle pain , 1990, International archives of occupational and environmental health.

[12]  R H Westgaard,et al.  Generation of muscle tension additional to postural muscle load. , 1987, Ergonomics.

[13]  G. Somjen,et al.  Excitability and inhibitability of motoneurons of different sizes. , 1965, Journal of neurophysiology.

[14]  A. English,et al.  An electromyographic analysis of compartments in cat lateral gastrocnemius muscle during unrestrained locomotion. , 1984, Journal of neurophysiology.

[15]  D. Winter,et al.  Crosstalk in surface electromyography: Theoretical and practical estimates. , 1994, Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology.