Supraspinal control of spinal centers for antagonist muscles in man

Abstract

Monosynaptic testing with the H-reflex was used to determine reflex excitability of motoneurons of the gastrocnemius muscle during single voluntary movements: extension or flexion of the ankle. For the last 60 msec of the latent period before the onset of voluntary extension of the foot, reflex excitability of motoneurons of the gastrocnemius (the agonist in extension) gradually increases. With voluntary flexion of the ankle reflex excitability of motoneurons to the gastrocnemius (the antagonist in flexion) is unchanged throughout the latent period until the onset of movement. Simultaneously (accuracy to 10 msec) with the beginning of the myogram of voltary foot flexion, reflex excitability of motoneurons of the gastrocnemius (antagonist) drops sharply. These results provide a basis for discussing an hypothesis concerning supraspinal control of spinal centers for antagonist muscles in man.