The effect of the impedance of a thin hydrogel electrode on sensation during functional electrical stimulation

Surface functional electrical stimulation results in stimulation of cutaneous receptors and discomfort. The degree of non-uniformity of current distribution in the cutaneous layers in the vicinity of the electrode may influence the sensation experienced. This paper describes the effects on sensation of a thin, high impedance electrode designed to reduce the non-uniformity of current distribution. Sensation associated with stimulation via a self-adhesive electrode with much higher impedance than conventional electrodes was compared with a low impedance electrode in a single-blinded, crossover study. The high impedance electrode does not alter either the current at which sensation is first registered. However, at higher currents, the high impedance electrode allows 9% more current to be passed for an equivalent sensation to that experienced with the conventional electrode. A 28% decrease in discomfort with the use of the high impedance electrode was also reported.