The physical properties of recording electrodes coupled with the input
characteristics of recording amplifiers can affect motor unit paramet
ers. In recent years, there has been increased use of disposable needl
e electrodes; thus, a comparison of impedance characteristics with dis
posable types is of interest. Impedances at 10, 100, 1000, and 10,000
Hz of eight different electrode models including concentric and monopo
lar, both disposable and reusable, were measured. For all models of mo
nopolar electrodes, no significant difference in impedance was found b
etween disposable and nondisposable types. Intramodel variability was
seen, however, with a twofold difference between minimum and maximum i
mpedances for each model. For concentric electrodes, a moderate differ
ence in impedance was found between disposable and nondisposable types
, but less intramodel variability was seen; there was also more interm
odel variability. To determine whether the measured impedances could a
ffect recorded motor unit potentials, a theoretical analysis was condu
cted using typical waveforms along with circuit analysis techniques. E
lectrode impedances as high as 50 times nominal values caused no signi
ficant waveform distortion.