Sampling in the human motor control system

Some results of a physiological investigation of the sampling hypothesis in the human motor control system are presented in this paper. The hypothesis of a proprioceptively open loop system at the initiation of voluntary effort is not supported by data from ankle rotation. No discontinuity in the monosynaptic pathway (primary afferent fiber to alpha motoneuron) is observed during random isometric step tracking using the reflex as test signal in the gastrocnemius-soleus reflex arc. This would indicate that for the ankle control system, the hypothesis of sampling at the alpha motoneuron, as proposed by Navas and Stark for wrist rotation, is not valid. The sampling behavior in the human motor system, if it exists, must be of the central origin.