Changes in reciprocal Ia inhibition from wrist extensors to wrist flexors during voluntary movement in man.

Transmission in the Ia inhibitory pathway from wrist extensor muscles onto flexor MNs was studied at various times after the onset of voluntary wrist extension or flexion. At the very onset of wrist movements Ia inhibition was not changed, as compared to at rest, whereas later it progressively increased during wrist extension and decreased during wrist flexion. These results are discussed in relation to the different inputs converging onto Ia interneurones and it is suggested that their inhibition by Renshaw cells might be responsible for the results found at the onset of contraction.