H reflex

The H reflex with tibial nerve stimulation in the popliteal fossa, recording from the soleus muscle. The H reflex is visible only with submaximal stimulation. With a slow increase in stimulus strength, the H reflex appears as the stimulus changes from subthreshold to submaximal. The amplitude of the H reflex is greatest just below the threshold for the appearance of the compound muscle action potential (CMAP or M response). With increasing stimulus strength, the H reflex amplitude declines as M response amplitude increases. The H reflex disappears with maximal and supramaximal stimulation.