Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · Apr 1995
Clinical TrialDifferential effects of a flexor nerve input on the human soleus H-reflex during standing versus walking.
A conditioning (C) stimulus at group I strength was delivered during standing to the common peroneal (CP) nerve before a test (T) stimulus at several C-T intervals ranging from 0 to 150 ms. At sufficiently long C-T intervals (100-120 ms) the soleus H-reflex was strongly inhibited despite little, or no change, in the background level of EMG activity. This finding indicates that a significant portion of the inhibition occurs at a premotoneuronal level, likely via presynaptic inhibition of the Ia-afferent terminals. ⋯ Firstly, during walking the intraspinal terminals of the afferent fibres (group Ia and Ib) conducting the conditioning volley may be presynaptically inhibited, or their input gated at the interneuronal level. Secondly, on the assumption that the conditioning stimulus is acting via the presynaptic inhibitory network in the spinal cord, it is possible that during walking this network is saturated as a result of increased central or peripheral synaptic inputs. Finally, it seems unlikely that differences in the refractoriness of the CP nerve between the tasks may be involved; the reasons for this are presented in the discussion.