The effects of the innervation zone and interelectrode distance on the patterns of responses for electromyographic amplitude and mean power frequency versus isometric torque for the vastus lateralis muscle

The purpose of the present study was to examine the effects of the innervation zone (IZ) and differences in interelectrode distance (IED) on the patterns of responses and mean values for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus isometric torque for the vastus lateralis. Ten men performed submaximal to maximal isometric muscle actions of the dominant leg extensors, and four separate bipolar surface EMG signals were detected from the vastus lateralis using a linear electrode array. Two electrode arrangements had IEDs of 10 and 30 mm and were located directly over the IZ. Two other electrode arrangements also had IEDs of 10 and 30 mm, but were distal to the IZ. The results indicated that in 50% of the cases, the IZ affected the patterns of responses for absolute and normalized EMG amplitude and MPF versus isometric torque. In 80% of the cases, however, there were no differences between the electrode arrangements with 10 and 30 mm IEDs for the absolute and normalized EMG amplitude and MPF versus isometric torque relationships. Both electrode placement over the IZ and differences in IED affected the mean values for absolute EMG amplitude, but not those for absolute EMG MPF. In addition, there were no mean differences among the four electrode arrangements for normalized EMG amplitude and MPF values. Thus, these findings supported normalization, and indicated that it is useful for reducing the influences of the IZ and differences in IED on absolute EMG amplitude and MPF data.