Optimal stimulus duration for the H reflex.

Authorities advocate different stimulus durations to produce an H reflex. In order to find the optimal stimulus duration for recording H reflexes, the recruitment curves for H reflexes and M responses were studied in 10 healthy subjects. The H reflex was recorded in the upper and lower extremities, and the durations of the electrical stimulus used ranged from 0.1 to 3 msec. The amplitude of the H reflex and the relation between the H reflex and M response changed with stimulus duration. H reflexes are brought out to advantage using a stimulus duration between 0.5 and 1 msec.