Effects of monopolar and bipolar electrode configurations on surface EMG spike analysis

This study compared the effects of monopolar and bipolar electrode configurations on interference pattern analysis of the surface electromyographic (sEMG). Twenty-four college-aged male participants performed isometric actions of the elbow flexors at 40, 60, 80, and 100 percent of maximal voluntary contraction (MVC). Separate (Ag/AgCl) electrodes were used for both configurations. There were five measures associated with "spike shape" analysis: mean spike amplitude (MSA), mean spike frequency (MSF), mean spike slope (MSS), mean spike duration (MSD) and mean number of peaks per spike (MNPPS). A load-cell and wrist-cuff assembly was used to record isometric elbow flexion forces. Both electrode configurations resulted in the same trends force changes in spike shape measures across force levels: there was a linear increase in MSA, MSS, and a quadratic decrease in MSF and the MNPPS (p's<0.05). The MSD underwent a quadratic increase (p<0.05). The spike shape measures had greater mean magnitudes and exhibited greater rates of changes across force levels for the monopolar electrode configuration (p's<0.05). The monopolar electrode configuration was therefore more sensitive to changes in muscle activity with increases in isometric force. This is an important consideration because the rate at which muscle electrical activity develops into a full interference pattern is an important qualitative and quantitative diagnostic measure.