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.

Interindividual variation of physical load in a work task

“…One possible explanation for the large variation is methodological. We paid particular attention to the electrode placement; they were not placed over the end-plate region (29). Thus the risk for cross-talk from signals originating in adjacent muscles was small.…”

Alterations in Shoulder Kinematics and Associated Muscle Activity in People With Symptoms of Shoulder Impingement

“…Experimental Procedure Surface electrodes were placed over the upper trapezius muscle (two thirds of the distance from the spinous process of the seventh cervical vertebra to the acromial process), 50 the lower trapezius muscle (one fourth of the distance from the thoracic spine to the inferior angle of the scapula when the arm was fully flexed in the sagittal plane), 51 and the lower serratus anterior muscle (over the muscle fibers anterior to the latissimus dorsi muscle when the arm was flexed 90°in the sagittal plane) 52 ( Fig. 1A).…”

The Effects of Scapular Taping on the Surface Electromyographic Signal Amplitude of Shoulder Girdle Muscles During Upper Extremity Elevation in Individuals With Suspected Shoulder Impingement Syndrome

“…Electrode placement (FIGURE 1) was based on the work of Cram and Kasman 10 and Jensen et al 19 The electrodes for the upper trapezius muscle were placed approximately 2 cm lateral to the midpoint of an imaginary line connecting the spinous process of the seventh cervical vertebra and the acromion ( just lateral to where the scapular tape was placed). Electrode placement for the lower trapezius muscle was approximately 10.5 cm inferomedial to the medial border of the spine of the scapula, at a 55° oblique angle to the horizontal plane, but not below T12.…”

“…In addition, the location of the upper trapezius electrode was midway between the C7 spinous process and the acromion in the Cools et al 7 study, which has been reported to depress the signal amplitude of the upper trapezius. 19 They applied the tape lateral to the electrodes and laterally over the upper trapezius. Perhaps the most important difference between the 2 studies involves the subject populations: the current study used injured individuals rather than noninjured subjects.…”