title: The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle.
abstract: 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.
authors.affiliation: Division of Organization and Work Science, Norwegian Institute of Technology, Trondheim.
authors.forename: C
authors.initials: C
authors.lastname: Jensen
authors.forename: O
authors.initials: O
authors.lastname: Vasseljen
authors.forename: R H
authors.initials: RH
authors.lastname: Westgaard
mesh_terms: D000328:Adult; D001132:Arm / Q000502:physiology; D004566:Electrodes; D004576:Electromyography / Q000379:methods*; D005246:Feedback; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D009132:Muscles / Q000502:physiology*; D011187:Posture; D012782:Shoulder / Q000502:physiology*