The relative contribution to the plantar-flexor torque of the soleus motorunits activated by the H reflex and M response in humans

This study proposes a method of quantifying the relative contribution to th e plantar-flexor torque of soleus H and M responses evoked by tibial nerve stimulation. For ten subjects, the amplitude of the twitch produced by the H wave was plotted against the corresponding potential, for stimuli produci ng H without M (i.e. in the ascending portion of the H-recruitment curve). It was then assumed that the contribution of H to twitches produced by M pl us H was similar for similar H waves on the curve-descending portion. Hence , the contribution of M was estimated, for the range of M waves including t hose accompanying H-max. The estimated mechanical contributions of H and M wave increase linearly with their potentials, the slope of the relationship being greater for H than M. The interpretation of th is finding is discuss ed. A simple formula for assessing the contribution of the H wave to the tw itch torque is given. (C) 2000 Elsevier Science Ireland Ltd. All rights res erved.