[Changes in motor neuron excitability during the organization of voluntary movements].

In healthy subjects, H-testing revealed no specific changes of motoneuron excitability during the latency period of voluntary motor activity of movement agonist whereas the H-reflex was augmented prior to movements triggered by a sound signal, the augmentation being the result of the sound activating effect mainly (startle--response). Sharp augmentation of the H-reflex occurs at the beginning of agonist voluntary activation due to interaction between the reflex and the voluntary muscular activities (interaction of peripheral and supraspinal effects on the motoneurons).