Isao Takeda

Excitability of the spinal motor neuron pool and F-waves during isometric ipsilateral and contralateral contraction

We recorded the F-waves from opponens pollicis muscle during isometric contraction following stimulation of the right median nerve in male and female subjects. The F-waves were recorded in the following five conditions: 25, 50, 75 and 100% isometric contraction of the right opponens pollicis muscle, and 25% isometric contraction with simultaneous 100% contralateral contraction. The F-waves in 20 trials were analysed with respect to persistence, F/M amplitude ratio, latency, duration and phase of the wave. Persistence and the F/M amplitude ratio increased with increasing contraction strength; however, latency, duration and phase were unchanged. There was no significant difference between 100% contralateral contraction and contralateral relaxation on F-waves recorded from ipsilateral muscle, for all parameters. These results suggest that excitability of anterior horn cells in spinal cord increases with isometric contraction, but contralateral contraction has no such effect on excitability.