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Circumferential pressure (CP) applied to the lower leg reduces soleus motor neuron reflex excitability (MNRE); however, the mechanism of control is unknown.


To investigate the effect that CP has on disynaptic reciprocal inhibition (DSRI) and on Ia presynaptic inhibition (IaPI) of the soleus H-reflex in healthy subjects.


DSRI of soleus motoneurons and presynaptic control of soleus group Ia afferents were measured before, during and after CP was applied to the calf. Pressure was set to 40–45 mmHg. DSRI was evaluated by observing changes in the H-reflex amplitude after a conditioning stimulus was applied to the common peroneal nerve. IaPI was assessed using two separate protocols involving conditioning of the soleus H-reflex: femoral nerve facilitation (FNS) (heteronymous) and D1 and D2 inhibition (homonymous). A change in DSRI and IaPI was determined by comparing the Hpressure, Hpost-pressure phases to the Hpre-pressure phase of the conditioned H-reflexes.


A mean 12% decrease in FNS was observed during CP (p < 0.05). D1 and D2 inhibition decreased slightly. CP did not affect DSRI.


The results show that CP applied to the calf significantly increased heteronymous soleus IaPI, but affected homonymous IaPI less. It was concluded the CP does increase IaPI of soleus motoneurons but only modestly. The change was not large enough to explain the dramatic inhibition that occurs in the (unconditioned) H-reflex amplitude when CP is applied. Therefore, IaPI is not the primary inhibitory mechanism that CP uses to lower MNRE.

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