Role of volume-conductor properties of muscles in the formation of evoked contractions during stimulating electrical impedance myography.

Experiments on the preparation of frog sartorius muscle showed that electrical impedance myogram of evoked muscle contractions is the sum of electric processes accompanying contraction of some muscle fibers or muscle regions. Inverted muscle response probably results from heterotopic excitation of distant muscle regions under conditions of reduced excitability of muscle fibers adjacent to the electrode. During centrifugal propagation of contractions, especially in altered muscles, the negative wave on the myogram corresponding to impedance decrease is sometimes followed by a positive wave. The possibility for recording of heterotopic contractions indicates that the impedance of the electrode-muscle interface produces no considerable effects on the shape of electrical impedance myogram. These results hold much promise for the diagnostics of neuromuscular diseases.