Multifrequency characteristics of disposable and nondisposable EMG needle electrodes

The physical properties of recording electrodes coupled with the input characteristics of recording amplifiers can affect motor unit parameters. In recent years, there has been increased use of disposable needle electrodes; thus, a comparison of impedance characteristics with disposable types is of interest. Impedances at 10, 100, 1000, and 10,000 Hz of eight different electrode models including concentric and monopolar, both disposable and reusable, were measured. For all models of monopolar electrodes, no significant difference in impedance was found between disposable and nondisposable types. Intramodel variability was seen, however, with a twofold difference between minimum and maximum impedances for each model. For concentric electrodes, a moderate difference in impedance was found between disposable and nondisposable types, but less intramodel variability was seen; there was also more intermodel variability. To determine whether the measured impedances could affect recorded motor unit potentials, a theoretical analysis was conducted using typical waveforms along with circuit analysis techniques. Electrode impedances as high as 50 times nominal values caused no significant waveform distortion.