In this study, as a preliminary step for application to the patients with the disease, we investigated the characteristics of excitability of spinal motor nerve function during force adjustment with the thumb and index finger in healthy subjects, using F waves of evoked electromyograms. Furthermore, by using an originally developed analysis method that reflects the diversity of F waves, we examined the relationship between motor skills and the characteristics of the motor units that make up the F wave.
Thirty-one healthy subjects (male: 15 females: 16, mean age 22.0 ± 3.7 years) were included in the study. First, we measured F waves at 20% and 50% intensity of maximal muscle force in opposing movement of the thumb and index finger by the non-dominant hand and examined the relationship between F wave waveform changes with contraction intensity and motor skills. The analysis items were the coefficient of variation (CV) of the amplitude values (Am-CV), negative peak latency (NL-CV) and positive peak latency (PL-CV) that reflecting the diversity of the F wave. In addition, a histogram was created from the negative peak and positive peak latency, and the percentage of each peak waves appearing at the same latency (over rap) was calculated. Multiple comparisons were performed for the effect of contraction, and multiple regression analysis was performed for the relationship with motor skills.
Am-CV showed a significant tendency to decrease at 20% MVC relative to rest（p=0.093 r=0.39), and PL-CV was significantly decreased at 20% and 50% relative to rest(p=0.025 r=0.56, p=0.020 r=0.54 ). However, multiple regression analysis did not provide a regression equation explaining motor skills（p=0.393 r=0.09).
The waveform of the F wave suggested that the waveform appeared at a similar latency with muscle force. This is the change in the firing type of the motor unit when forced to exert a certain amount of force. We suggested that differences in motor strategy existed for individual differences in motor skills, and that no relationship with F-wave diversity was found.
F-waves can be used to characterize features including motor units, which can be used as a useful evaluation method in seeking improvement in hand function. However, the relationship with motor skills needs to be further investigated because there may be many influencing factors, including visual information and experience.
finger function
contraction
