Timing as a prominent factor of the Jendrassik manoeuvre on the H reflex.

The influence of the Jendrassik manoeuvre on the myotatic reflex was analysed using a strain gauge as an indicator of the upper extremity movement and the H reflex of the soleus muscle as the test reflex. The most prominent factor responsible for the enhancement was not the speed or the strength of the manoeuvre but the timing from the instruction.