Fatigue-incduced modulation of human soleus Hoffmann reflex under conditions of homosynaptic postactivation depression due to pair tibial nerve stimulation

The purpose of our work was to investigate in detail the influence of pair stimulation of tibial nerve (n.tibialis) on human soleus H-reflex amplitude at rest and after long-lasting voluntary contraction of calf muscle (m.m. gastrocnemius-soleus), which caused the fatigue of soleus muscle. The method of H-reflex of soleus muscle was used. Test and conditioned responses (by pair stimulation of n. tibialis) were registered. Homosynaptic postactivation depression led to inhibition of H-reflex at rest. After fatiguing voluntary static contraction the amplitudes of test and conditioned soleus H-reflex were significantly reduced. Then both H-reflex amplitudes subsequently recovered. Soleus H-reflex inhibition might be due to the activation of the groups III and IV afferent nerves under the influence of mechanical and metabolic changes in the muscle.