The effects of electrode orientation on electromyographic amplitude and mean power frequency during cycle ergometry

The purposes of this study were threefold: (1) to compare the power output related patterns of absolute and normalized EMG amplitude and MPF responses for electrode orientations that were approximately parallel and perpendicular to the muscle fibers of the vastus lateralis muscle (VL); (2) to examine the influence of electrode orientation on mean absolute EMG amplitude and MPF values; and (3) to determine the effects of normalization on mean EMG amplitude and MPF values from parallel and perpendicular electrode orientations. Twenty adults (10 men and 10 women mean+/-SD age=23.4+/-3.6 years) performed incremental cycle ergometry tests to exhaustion. Two sets of bipolar surface EMG electrodes were placed approximately parallel and perpendicular to the muscle fibers over the VL. Paired t-tests indicated that absolute EMG amplitude values for the parallel electrode orientation were greater (p<0.05) at 50, 75, and 100W. The normalized EMG amplitude also had greater values for the parallel electrode orientation at 75 and 100W. For absolute EMG MPF, the parallel electrode orientation had greater values for all six power outputs, but after normalization, the perpendicular electrode orientation had a greater value at 75W. Ten percent of the subjects exhibited different power output related patterns of responses between electrode orientations for EMG amplitude and 35% exhibited different patterns for MPF. These findings indicated that normalization reduced, but did not eliminate the influence of electrode orientation and highlighted the importance of standardizing electrode orientation to compare EMG values during cycle ergometry.