The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle

  • Chris Jensen
  • Ottar Vasseljen
  • Rolf H. Westgaard


The effect of electrode position on the upper trapezius muscle on the myo-electric signal amplitude was investigated with special reference to arm position and estimate of force output. Previously, a depression of the electromyogram (EMG) signal has been reported midway between the seventh cervical vertebrae (C7) and acromion (Veiersted 1991, Eur J Appl Physiol 62:91–98) although this electrode position has been recommended (Zipp 1982, Eur J Appl Physiol 50:41–54). Ten healthy subjects performed maximal shoulder elevations with the arm in vertical, abducted and flexed positions and they performed a dynamic movement test. The myo-electric signal was recorded along the length of the right upper trapezius muscle by a 16-channel bipolar array electrode and was integrated with a 0.2-s time resolution. A region just lateral to the midpoint between C7 and the lateral edge of acromion was found with high and stable amplitudes (% coefficient of variation equalled 5.6). At the midpoint a dip in the amplitude profile appeared which was slightly displaced by arm abduction or flexion probably due to sliding, of the skin relative to the muscle. A linear EMG-force relationship was found in the region with high signal amplitudes, whereas the more lateral and the dip region showed highly variable EMG-force relationships. Thus, it was found that when using bipolar surface electrodes with an interelectrode distance of 2 cm a centre position 2 cm lateral to the midpoint between C7 and acromion provided good repeatability and high signal yield.

Key words

Trapezius muscle Electromyography Electrode position Force Arm position 


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Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Chris Jensen
    • 1
  • Ottar Vasseljen
    • 1
  • Rolf H. Westgaard
    • 1
  1. 1.Division of Organization and Work ScienceThe Norwegian Institute of TechnologyTrondheimNorway

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