The influence of electrode placement over the innervation zone on electromyographic amplitude and mean power frequency versus isokinetic and isometric torque relationships

The purpose of this investigation was to examine the influence of electrode placement over the estimated innervation zone (IZ) for the vastus lateralis, as well as proximal and distal to the estimated IZ, on the torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF) during isokinetic and isometric muscle actions of the leg extensors. Eleven men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximal and distal to the estimated IZ. The results indicated that the absolute and normalized EMG amplitude versus torque relationships were best fit with the same regression model for the proximal, IZ, and distal electrode placement sites in 7 of the 11 subjects during the isokinetic muscle actions. There were no consistent patterns between subjects or electrode placement sites for the absolute and normalized EMG MPF versus isokinetic torque relationships. During the isometric muscle actions, the absolute and normalized EMG amplitude versus torque relationships were best fit with the same regression model for the three electrode placement sites in 7 of the 11 subjects. There were no consistent patterns between subjects or electrode placement sites for the absolute and normalized EMG MPF versus isometric torque relationships. These findings suggested that factors related to electrode placement (but not necessarily the IZ) may influence the patterns of responses for EMG amplitude versus torque during isometric muscle actions of the vastus lateralis, but not for dynamic muscle actions.