Modulation of soleus H-reflex following ipsilateral mechanical loading of the sole of the foot in normal and complete spinal cord injured humans

The modulation of the soleus H-reflex in response to tonic mechanical loading applied to the plantar aspect of the foot sole was examined in nine normal subjects and five patients with a clinically defined complete spinal cord injury (SCI). With the subjects seated, tonic pressure applied to the metatarsal region of the ipsilateral foot sole significantly depressed soleus H-reflex excitability in all subjects. The demonstration of a decrease in H-reflex excitability in both subject groups as a result of applied pressure to the foot suggests that the change in reflex excitability is the result of a common spinal mechanism. The results highlight the modulatory effects that natural stimulation of cutaneous afferents can have on reflex excitability and may have practical application in gait rehabilitation and in the management of disorders of muscle tone following SCI.