The effects of ankle position on H-reflex were studied in 40 healthy subjects. Ankle position was maintained passively by means of the foot-plate in control position, that is neutral (dorsiflexion 0° and plantarflexion 0°), dorsiflexion 10 degree, 20 degree, plantarflexion 10 degree, 20 degree, and maximal plantarflexion. H-reflex excitability was evaluated by the ratio of the threshold of H-reflex to that of M-wave (H/M threshold), and the ratio of maximal amplitude of H-reflex to that of M-wave (H/M amplitude).

The results showed that H/M threshold and H/M amplitude were decreased at dorsiflexed position compared with those at neutral position. Thus dorsiflexed ankle position might modulate the α-motor neuron excitability of H-reflex. But there were no significant changes in H/M threshold and H/M amplitude during plantarflexion up to 20° compared with those at neutral position. At maximal plantarflexed position it was also observed that there was decremental H/M amplitude, but there was no change in H/M threshold, so, it might be due to change of recording muscle status. H-reflex of just below M-wave threshold resembled the maximal H-reflex, and it also might represents the α-motor neuron excitability of H-reflex.

In case of prone position with ankle out of bed, ankle position would be about 20 degree plantarflexed if a person had no ankle joint contracture. It is suggested that measuring the H-reflex, there is no need to make the ankle neutral strictly, if not dorsiflexed.