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Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque

European Journal of Applied Physiology and Occupational Physiology volume 61, pages 370–379 (1990)Cite this article

Summary

The electromyographical (EMG) response to isometric ramp contractions of the right arm, the left arm, and both arms was studied using four pairs of surface electrodes above the right upper trapezius muscle (UT) of six men and six women. Contractions were made against gravity with the active arm(s) in eight positions, ranging from flexion to abduction. To describe arm positions, a new, simple terminology was developed. Root mean square (rms)-converted EMG-signals were normalized (EMGnorm) with respect to a reference contraction. The EMGnorm corresponding to a 15 N · m torque in the right glenohumeral (GH) joint was strongly related to the position of the right arm (P<0.001). The shape of this relationship depended on the electrode position (P<0.001). The ratio between EMGnorm at 30 N · m and 15 N · m GH torques was related to arm position (P < 0.001) and differed between electrodes (P< 0.001). A left-side GH torque resulted in right-side (contralateral) EMG activity, typically corresponding to 20%–30% of that obtained during similar right-side GH torque. Bilateral GH torque implied 0%50% increase in EMG activity as compared to that obtained with the right arm alone. The results have shown that signals from one pair of surface electrodes above UT cannot be taken as representative of the EMG activity from electrodes located elsewhere above UT. The EMG recordings reflected a complex pattern of muscular activation, significantly related to both outwardly visible factors (arm position, GH torque), and within-body servosystems (motor control reflexes).

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Affiliations

  1. National Institute of Occupational Health, Division of Applied Work Physiology, S-17184, Solna, Sweden

    Svend Erik Mathiassen & Jørgen Winkel

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  1. Svend Erik Mathiassen
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  2. Jørgen Winkel
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Mathiassen, S.E., Winkel, J. Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque. Europ. J. Appl. Physiol. 61, 370–379 (1990). https://doi.org/10.1007/BF00236055

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  • DOI: https://doi.org/10.1007/BF00236055

Key words

  • Electromyography
  • Neck-shoulder
  • Isometric
  • Posture
  • Co-activation