The flexor reflex--influence of stimulus parameters on the reflex response.

The flexor reflex evoked in the tibialis anterior muscle by stimulation of the medial plantar nerve was investigated in 54 normal subjects. Three main reflex components were identified (excitation--inhibition-- excitation), the early excitation being composed of two subcomponents. Occasionally, a fourth (excitatory) reflex component was seen breaking through EMG inhibition. The individual reflex components were differentially susceptible to facilitatory influences which suggested transmission via a central multichannel system. Methodological experiments showed that the amplitudes and to some degree also the latencies of the individual reflex components were modified by both the parameters of the stimulus as well as by the degree of pre-innervation. However, the patterning of the reflex response was basically independent from methodological permutations.