Some principles of flexor reflex generation in human leg muscles.

Flexor reflexes, evoked by stimulation of the tibial and deep peroneal nerves at the ankle level, were investigated in several ipsi and contralateral human leg muscles. On both sides, the reflex consist of a stereotyped oscillating sequence of inhibition and facilitation, exhibiting specifity to the stimulated site only in the initial ipsilateral phases. The responsible afferents were identified as belonging to a group of non-nociceptice skin afferents with a maximum conduction velocity of about 40-54 m/sec. Interdependence was observed between both latencies and amplitudes of the individual phases of the reflex sequences in synergistic and antagonistic pairs of muscles. It is concluded that the function of such a conjoint reflex generation in different muscles is to ensure an organized and adequate withdrawal.