The independence of premovement H reflex gain and kinesthetic requirements for task performance

The gain of the H reflex pathway is extensively altered prior to a voluntary contraction. We hypothesized that this gain change is modulated for the kinesthetic requirements of the ensuing task. The experiment involved a simple reaction time task, in which soleus H reflexes were evoked during the final 100 msec before the electromyographic activity for simple ankle movements of low, medium and high requirement for accurate positioning of the foot. The latter two conditions involved tracking and perturbed tracking, respectively. Subjects were required to respond with a non-ballistic movement. Over the 6 subjects and tasks, before plantar flexion, mean reflex magnitudes significantly increased (P < 0.05; to 160% of control, S.D. 60%). Before dorsiflexion they decreased (to 87% of control, S.D. 10%). However, the two accuracy requirements did not significantly alter the soleus H reflex changes, before either plantar flexion or dorsiflexion (P > 0.05). We conclude that the premovement gating of the spinal route from Ia afferents to the autogenic soleus muscle is independent of the changes in the presently tested types of kinesthetic requirements for movement.