F-waves of healthy subjects elicited by voluntary movements of different muscle contraction strengths: consideration of the type of F-wave waveforms

Abstract

The F-wave is characterized by different waveforms after each stimulation. We observed that the numbers and types of F-wave waveform during resting by healthy subjects were the same in number. From this result, we presumed that various F-wave waveforms indicate therapeutic effects in the progress of physical therapy. In addition, we considered that analysis of the type of F-wave waveform would provide an index for assessing the improvement of neurological function. In this study, we analyzed the type of F-wave waveforms elicited in healthy subjects by isometric contraction of pinch movements of the thumb and index finger. F-wave waveforms of the subjects were recorded during rest, pinching of a pressure sensor by the thumb and index finger, and pinching at 25% and 50% maximum voluntary contraction. In addition, we recorded the F-wave occurrence and calculated the F/M amplitude ratios of the recorded F-wave waveforms, and carried out F-wave waveform analysis. The F-wave occurrence and the F/M amplitude ratio increased with the isometric contraction intensity in comparison with the rest phase. Further, the F-wave waveforms were different in each trial. Consequently, this result suggests the excitability of the spinal motor neurons and the type of F-wave waveform generated by the anterior horn cell increase in tandem with the isometric contraction intensity.