An investigation of the Jendrassik manoeuvre.
Several mechanisms were investigated by which the Jendrassik manoeuvre might potentiate tendon jerk and H-reflexes, recorded here as surface EMG from the triceps surae muscle group. If fusimotor activation is involved, then, after muscle conditioning designed to leave spindles in a slack state, interposing a Jendrassik manoeuvre before reflex testing should have increased reflex amplitude by restoring spindle sensitivity; but this was not the case. The Jendrassik manoeuvre failed to increase facilitation of the soleus H-reflex by a quadriceps volley, contrary to expectations if it operates by presynaptic disinhibition. There was no increase in the level of ongoing EMG during a Jendrassik manoeuvre, indicating that it does not operate by direct facilitation of motoneurones. The Jendrassik manoeuvre produced less reflex potentiation when spindles had a high rate of resting discharge. A remaining, untested mechanism is the modulation of oligosynaptic pathways that may contribute to the largely monosynaptic reflex response.
Gregory
J E
JE
Department of Physiology, Monash University, Victoria, Australia. Ed.Gregory@med.monash.edu.au
Wood
S A
SA
Proske
U
U
D004576:Electromyography; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D009047:Motor Neurons, Gamma / Q000502:physiology*; D009132:Muscles / Q000502:physiology