Decrease in the excitability of spinal nerve function corresponding to the soleus muscle during terminal phase of heel-raise imagery

[Purpose] This study investigated the excitability of spinal nerve function in healthy participants by asking them to imagine raising and lowering their heels in a standing position while varying the timing of stimulation to induce an H-reflex from the soleus muscle during imagery. [Participants and Methods] Participants were instructed to begin their imagery at the fourth metronome sound and imagine that their heels would be maximally raised at the time of the optical signal, which occurred 1,000 ms after the metronome sound; moreover, they would be standing at the metronome sound 1,000 ms later. They were instructed to perform the imagery 21 consecutive times. The timing of the electrical stimulation was set for five conditions: 0, 200, 400, 600, and 800 ms after the metronome sound. [Results] Amplitude H/Mmax ratios were significantly higher at the 0, 200, 400, and 600 ms conditions than in the resting and 800 ms conditions. [Conclusion] The imagery task has the potential to increase the excitability of spinal nerve function from 0 ms to 600 ms after a metronome sound but then decrease it to the resting state at 800 ms.