Simultaneous Hoffmann reflex measurements in multiple muscles around the ankle.

Measurement of the Hoffmann reflex (H-reflex) provides an estimate of alpha motoneuron activity in the target motoneuron (MN) pool. The H-reflex has been assessed for a wide variety of reasons in neuroscience research. However, the majority of protocols have focused on the assessment of only one muscle and its corresponding motoneuron pool at any instant. Previously established protocols do not simultaneously assess reflex activity in multiple muscles elicited from a single stimulation. This new protocol allows for assessment of alpha motoneuron activity in three muscles around the ankle joint from a single stimulus to the sciatic nerve. To elicit the responses, the sciatic nerve was stimulated just prior to its bifurcation into the tibial and common peroneal nerves in the popliteal fossa. Electromyographic recording electrodes were placed on the tibialis anterior, peroneal longus, and soleus muscles. The 1-ms square wave pulse was delivered every 15 s during the recruitment curve mapping. The maximum H reflex and M waves were measured in each muscle and their ratios calculated. The measurement of these ratios simultaneously allows for assessment of the cumulative alpha motoneuron activity about the ankle at a given point in time.