title: Can the F-Response be Volitionally Repressed during Functional Electrical Stimulation?
abstract: Objective  The purpose of this study was to test if the F-response can be repressed volitionally. Normally, the F-response is used for clinical diagnostics but it also has an important influence on the design of a neural prosthesis involving functional electrical stimulation (FES) and the use of volitional myoelectric signal (MES) for control. Methods  Ten neurologically normal subjects were trained to reduce the level of the F-response from the anterior tibial muscle. The nerve to the anterior tibial (TA) muscle was stimulated with constant intensity and frequency (16.6 pulses per second) and the surface myoelectric signal (MES) from the muscle was digitally processed to estimate the F-level. Training was carried out by giving the subject visual feedback on a computer screen of the F-level during the stimulation with the task of keeping the level as low as possible. Each subject had five sessions consisting of 20 stimulation tests, lasting 30 sec each. The subjects acted as their own control and changes in the F-level during the stimulation tests, sessions, and trials, were analyzed. Results  There was a significant (p < 0.001) increase in the F-response level within the test period of constant stimulation, but a significant (p < 0.001) decrease from the first to the last test in the session was found. From the first to the last session of a trial, the change was found not significant. Conclusion  The level of the F-response may change locally, but there is no indication that a subject can volitionally learn to repress the response, even when given feedback information about the actual level. Therefore the F-waves in the myoelectric signal from a stimulated muscle has to be accounted for when designing devices using a stimulated muscle response for myoelectric control such as eliminating the F-interval from the recorded signal.
authors.affiliation: Centro di Bioingegneria FDG, Found. Don Carlo Gnocchi ONLUS IRCCS, Milano, Italy.
authors.forename: Rune
authors.initials: R
authors.lastname: Thorsen
authors.forename: Ilaria
authors.initials: I
authors.lastname: Carpinella
authors.forename: Maurizio
authors.initials: M
authors.lastname: Ferrarin