Abstract
The inhibitory effect of IB interneurons on motoneurons was tested in both legs of six hemiplegic adults. On the normal side, an inhibition of 10 ms, (14.6%) was observed in all cases and was similar to that described previously. On the spastic side, the same technique results in a facilitation of same duration reaching a maximum of 15%. Hence the IB inhibitory effect is, at least functionally, absent in spasticity. Disappearance of IB inhibition is an additional mechanism to be considered in interpreting spasticity.