Mechanism of monosynaptic reflex reinforcement during Jendrassik manoeuvre in man

The facilitating effect of the Jendrassik manoeuvre on monosynaptic reflexes in man has been studied by comparing H and T reflexes of the soleus and by blocking the effects of spindle activation by ischaemia of the leg. The Jendrassik manoeuvre equally enhances H and T reflexes provided that the test reflexes are small. The H reflex remains facilitated when the spindle activation cannot affect the soleus alpha-motoneurones--that is, when the Ia afferent nerve fibres from the soleus are blocked by ischaemia. It is concluded that the facilitating effect of the Jendrassik manoeuvre on the alpha-motoneurones is not predominantly routed via the gamma-loop.