The Effects Of Parallel Versus Perpendicular Electrode Orientations On EMG Amplitude And Mean Power Frequency From The Biceps Brachii

Abstract

PURPOSE: The purpose of this study was to examine the influence of electrode orientation on the electromyographic (EMG) amplitude and mean power frequency (MPF) versus isometric torque relationships for the biceps brachii muscle. METHODS: Ten adults [five men (mean ± SD age = 23.8 ± 2.8 years) and five women (mean ± SD age = 23.8 ± 2.2 years)] volunteered to participate in the investigation. Two separate bipolar surface EMG electrode arrangements (20 mm center to center) were placed on the dominant arm over the biceps brachii muscle. One EMG arrangement was placed parallel and the other perpendicular to the direction of the muscle fibers of the biceps brachii. The subjects performed two maximal, 6-second isometric muscle actions at a forearm flexion angle of 60° above the horizontal plane to determine maximal voluntary isometric contraction (MVIC). The subjects then performed a series of randomly ordered submaximal muscle actions in 10% increments from 10 to 90% MVIC. Paired t-test were used to examine mean differences between the two electrode orientations for absolute and normalized EMG amplitude and MPF values at each torque levels. RESULTS: The mean absolute EMG amplitude values for the parallel electrode orientation were greater (p < 0.05) than those for the perpendicular orientation at all isometric torque levels except 10% MVIC. For normalized EMG amplitude, there were no significant (p > 0.05) mean differences between the parallel and perpendicular EMG electrode orientations for any of the %MVIC values. Furthermore, there were no significant mean differences between the parallel and perpendicular EMG electrode orientations for absolute or normalized EMG MPF for any of the %MVIC values. CONCLUSIONS: These findings indicated that, unlike absolute EMG amplitude, normalized EMG amplitude values were not affected by electrode orientation. Thus, normalization can be used to reduce the effects of electrode orientation on EMG amplitude during isometric muscle actions of the biceps brachii. Furthermore, electrode orientation had no effect on absolute or normalized EMG MPF.