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EMG simulations are traditionally based on purely resistive models, in which capacitive effects are assumed to be negligible. The results of recent experimental studies, however, suggest these assumptions may not be valid for muscle tissue. Furthermore, both muscle conductivity and permittivity are frequency-dependent (dispersive). In this paper, the impact of capacitive effects and dispersion on the potential at the surface of the volume conductor is examined using a frequency domain finite element model. The results indicate that the effect of muscle capacitance and dispersion varies dramatically, depending on the values that are chosen. Choosing low conductivity and high permittivity values in the range of experimentally reported data for muscle can cause displacement currents that are larger than conduction currents with corresponding reduction in surface potential of up to 50% at 100 Hz. Values lying towards the middle of the reported range yield results which do not differ significantly from purely resistive models. Excluding dispersion can also cause significant error-up to 75% in the high frequency range of the EMG. It is clear that there is a need to establish accurate values of both conductivity and permittivity for human muscle tissue in vivo in order to quantify the influence of capacitance and dispersion on the EMG signal.
Date of Conference: 2001