Reflexes evoked in human thenar muscles during voluntary activity and their conduction pathways.

Responses evoked by an electrical stimulus to the median nerve in a small muscle of the human hand during a voluntary contraction have been examined. Two of these responses have been shown to be evoked through reflex pathways. The first, with a mean afferent conduction velocity of 64 m/s and estimated central delay of about 0.8 ms, is identified as an H reflex. The second response, which has an undefined central pathway, has a mean afferent conduction velocity of 43 m/s and an estimated central delay of about 17 ms.