Soleus Hoffmann-reflex modulation during walking in healthy elderly and young adults.

Soleus Hoffmann-reflex (H-reflex) modulation during walking was examined in 7 young and 13 elderly adults. H-reflex size was measured in 16 equal time divisions (phases) of the step cycle. In both the elderly and the young groups, the H reflex was minimal at the time of heel contact, rose to a maximum shortly after midstance, decreased rapidly as toe-off neared, then was minimal during swing. There was a significant interaction between age group and step cycle phase (p < .05). During midstance of walking, the elderly participants had a smaller H-reflex size during two of the 16 time phases of the step cycle (p < .05), despite no significant difference in H-reflex size between the age groups while standing. The smaller H-reflex size during the stance phase of walking may reflect changes in central reflex mechanisms that may impact stretch reflex contribution to ankle extensor neural drive and ankle stiffness in elderly persons during walking.