Stimulation Discomfort Comparison of Asynchronous and Synchronous Methods with Multi-Field Surface Electrodes

Functional Electrical Stimulation (FES) is a technique that artificially stimulates motor nerves in order to restore motor/sensory functions for assistive and therapeutic applications. Recently, multi-field surface electrodes for transcutaneous electrical stimulation have been suggested to overcome problems of single channel surface stimulation. This study compares sensation perceived by 15 healthy subjects on upper limb when two different stimulation methods are applied by means of multi-field electrodes. Asynchronous and synchronous stimulation methods are compared for four different cases: activation of two neighbor fields, three neighbor fields, two distant fields and three distant fields. Two descriptors rated from 1 to 5 are used to describe discomfort: superficial discomfort and deep discomfort. Results expressed no differences in superficial discomfort for any case, but showed significant differences in deep discomfort for distant field activations. In these cases, synchronous stimulation resulted in higher perceived deep discomfort than asynchronous stimulation and affected its efficacy.