Changes in the H-Reflex Amplitude Caused by Fluctuation of Stimulus Frequency.

We investigated the changes in the H-reflex amplitude at various stimulus frequencies, in order to identify the stable index in a relatively short period. 10 subjects volunteered for experiment. The H-reflex was obtained from the left soleus. The H wave was induced by 29 degrees of stimulus frequency: 10 degrees from 0.1 to 1.0 Hz with an increase of 0.1 Hz, and 19 degrees from 1.0 to 20.0 Hz with an increase of 1.0 Hz. The decrease in H wave amplitude tended to become greater with an increase in stimulus frequency. The frequency depression curve at stimulus frequencies from 1.0 to 20.0 Hz indicated a significant frequency depression (p<0.01) with an increase in stimulus frequency. Disinhibition of the H-reflex amplitude at stimulus frequencies from 4.0 to 8.0 Hz is a specific response, and the change rate of the H-reflex amplitude at the stimulus frequency of 6.0 Hz (62.9%) was almost the same as that of 1.0 Hz (62.5%). We found that repetitive evoked EMG using a stimulus frequency of approximately 5 Hz is a great value in examining the change in the H-reflex amplitude and has a good possibility of clinical application.