Topical anesthetics: effects on the Achilles tendon and H-reflexes. I. Able-bodied subjects.

Achilles tendon reflexes (ATR) and H-reflexes were monitored to determine changes in motor responses after the application of a benzocaine spray or an air spray to normal individuals. There was no change in ATR after application of the spray or the benzocaine, even when the sequence of reflex elicitation was reversed. The only significant change (p less than 0.05) in the H-reflex was an increase in its amplitude from baseline at all posttest times following (1) the placebo application when the H-reflex preceded the ATR (0.264 +/- 0.054V, ten minutes; 0.290 +/- 0.054V, 20 minutes; and 0.322 +/- 0.058V, 30 minutes), and (2) the benzocaine spray when the ATR preceded the H-reflex (0.277 +/- 0.084V, ten minutes; 0.309 +/- 0.152V, 20 minutes; and 0.329 +/- 0.131V, 30 minutes). Within-group comparisons revealed that a significantly greater H-reflex (p less than 0.05) was obtained at 20 and 30 minutes after air spray when H-reflex/ATR test sequence was used, whereas at 30 minutes after application of the benzocaine spray a significantly greater H-reflex was seen using the ATR/H-reflex test sequence. Changes in H-reflex amplitude appear to be as much a function of the reflex testing sequence as whether an air or benzocaine spray is used.