Influence of electrode position on changes in electromyograph parameters of the upper trapezius muscle during submaximal sustained contractions

Abstract

The purpose of the present study was to evaluate whether differences could be found in the changes in mean power frequency (MPF) and root-mean-square (rms) due to electrode positions on the upper trapezius muscle during a sustained submaximal task. A group of 25 healthy subjects performed a continuous forward flexion of the right arm at 20% of their maximal voluntary contraction (MVC). Three pairs of bipolar surface electrodes were positioned on a straight line between the spine of the seventh cervical vertebra (C7) and the lateral edge of the acromion. The fourth pair (the caudal position) was placed 2 cm below the midpoint of this line. The analysis of variance revealed significant differences between the electrode positions during the short 20% MVC and during MVC (P < or = 0.01). Furthermore, lower rms values were found when the electrodes were placed symmetrically around the midpoint of the reference line, which confirms previous studies. A statistical model has been developed to discriminate additionally the very small changes in the electromyogram parameters due to electrode position during the sustained 20% MVC. It was found that the slope coefficients of rms and MPF were significantly different from 0 (P < or = 0.01), although to a lesser degree for rms and more clearly for MPF of the caudal position (P < or = 0.05). Furthermore, significant differences were found between several combinations of the uppermost electrodes and the caudal position (P < or = 0.01). From this study, it is concluded that it is important to evaluate several electrode positions on the upper trapezius muscle to be able to represent the behaviour of this muscle accurately during a sustained contraction.

Pathophysiology of upper extremity muscle disorders

“…This could be the case when type I MUs or mechanically specialized subpopulations of MUs [156] are spatially clustered, such as in muscle compartments that have been identified in animal experiments [151]. In several arm and shoulder muscles, among them the trapezius muscle, indications for compartmentalization have been found [15,50,59,60,92,104]. In addition, prolonged pressure at lower levels (8 h, 30 mmHg) can cause muscle fiber damage at normal blood pressure [46].…”

Effect of electrode array position and subcutaneous tissue thickness on conduction velocity estimation in upper trapezius muscle

“…Several studies investigated the influence of the electrode position on global EMG parameters such as amplitude and power spectral frequencies (Jensen et al, 1993;Hermans and Spaepen, 1997;Kleine et al, 2000;McLean et al, 2003;Johnson and Pandyan, 2005). A few studies were focused on the effect of subcutaneous tissue layer thickness on EMG parameters both in simulated (Farina et al, 2002b and experimental conditions (Nordander et al, 2003).…”

Towards optimal multi-channel EMG electrode configurations in muscle force estimation: a high density EMG study

“…At the level of individual muscles [9,21], as well as at the level of muscle parts [22,28,33] and even of motor units (MU) [7,30] EMG activity varies over time. However, it remains unclear to what extent the variability of the EMG signal reflects variability in MU activity and to what extent it is based on the stochastic interference of the potentials of different MUs (e.g.…”