Can The High Repetition Rate Induced F-Wave Be Volitionally Controlled?

The F-wave is a randomly occurring response to electric stimulation of the motor nerve that normally is only of clinical interest as a diagnostic tool. It's impact on functional electrical stimulation (FES) has generally not been considered. However it has significant influence on the myoelectrical signal (MES) registered from the stimulated muscle and may subsequently have an effect on the contraction properties of the muscle, that should not be neglected. When MES is used for controlling FES of the same muscle, the F-wave is an unwanted noise component. During FES the stimulation frequency, intensity and registration site differs significantly from the traditional clinical investigation eliciting the F-wave and lack in literature. This paper reports some informative measurements to validate if the F-wave can be volitionally suppressed, the effect of continuous stimulation and training with visual feedback to the subject. It has been found that the F-wave in the relaxed healthy muscle is about a tenth of the MES at full contraction. Furthermore it has been found that there is no significant change in the level during short term (20min exercise) or medium term (5 sessions) of the F-wave level but that there is an increased level during ½ min of constant stimulation. It is concluded that the F-wave therefore has to be considered as a noise that cannot be volitionally repressed.