Synchronous stimulation and monitoring of soleus H reflex during robotic body weight-supported ambulation in subjects with spinal cord injury

We evaluated the accuracy of a novel method for recording the soleus H reflex at specific points in the gait cycle during robotic locomotor training in subjects with spinal cord injury (SCI). Hip goniometric information from the Lokomat system defined midstance and midswing points within the gait cycle. Soleus H reflex stimulation was synchronized to these points during robotic-assisted ambulation at 1.8 and 2.5 km/h. Motor stimulus intensity was monitored and adjusted in real time. Analysis of 50 H reflex cycles during each speed and gait phase showed that stimulation accuracy was within 0.5 degrees of the defined hip joint position and that >85% of the H reflex cycles met the +/-10% M wave criterion that was established during quiet standing. This method allows increased consistency of afferent information into the segmental spinal and supraspinal circuitry and, thus, evaluation of H reflex characteristics during robotic ambulation in subjects with SCI.