EIS measurements for characterization of muscular tissue by means of equivalent electrical parameters

The objective of this work was to study the use of electrical impedance spectroscopy (EIS) measurement to characterize muscle electrical properties in different conditions. In vivo EIS measurements were carried out in the range 1-60 kHz on 32 forearm flexor muscles of healthy volunteers. Each subject underwent to a protocol consisting of three trials: rest condition, isometric contraction, 4 min relaxation. Measured data were fitted with Cole-Cole equivalent electrical circuit using the complex nonlinear least square method. Finally, the relative variations from the steady state of the electrical parameters of the equivalent electrical circuit were estimated. Results obtained are in agreement with the hypothesis that, in the frequency range considered, the current preferentially flows through the extracellular fluid, being the component of intracellular resistance negligible. Among circuital parameters, in fact, the relative variations from steady state of R0 changed highly significant (p < 0.001) both during contraction and after 4 min relaxation.