THE RELATIONSHIP BETWEEN THE SOLEUS H-REFLEX AMPLITUDE AND VIBRATORY INHIBITION IN CONTROLS AND SPASTIC SUBJECTS .1. EXPERIMENTAL RESULTS

The effect of continuous Achilles tendon vibration on the soleus H-ref lex amplitude was quantified over the entire H-reflex recruitment traj ectory in 30 controls and 33 patients with spasticity in the lower lim bs. The results show that with increasing stimulus intensities, vibrat ory inhibition of the H-reflex initially increases, then subsequently decreases. This is probably a direct consequence of how the activation thresholds of the motoneurons are distributed over the motoneuron poo l. In patients, vibratory inhibition of the H-reflex was less over the entire recruitment trajectory than in controls. The decrease in vibra tory inhibition in spasticity is commonly attributed to a decrease in presynaptic inhibition or post-activation depression. However, the ave rage H-reflex threshold was lower in the patients, suggesting a decrea se of the motoneuron activation thresholds. A lower reflex threshold i n spasticity, therefore, may contribute to the observed reduction of v ibratory inhibition. Copyright (C) 1996 Published by Elsevier Science Ltd.