Soleus H-reflex gain in healthy elderly and young adults when lying, standing, and balancing.

Soleus Hoffman-reflex (H-reflex) gain was compared at the same background level of electromyographic activity across lying, natural standing, and tandem stance postures, in 12 young and 16 elderly adults. When compared to a lying posture, young adults significantly depressed soleus H-reflex gain when in a natural standing (19% decrease) and a tandem stance position (30% decrease; p <.0125 for both positions). For elderly adults, there was no significant decrease in H-reflex gain while standing naturally, but there was a significant 28% decrease when performing tandem stance (p <.0125). The data indicate that, although the mild motor control challenge of natural standing does not induce a decrease in soleus H-reflex gain in the elderly adults, as it does in young adults, in the more difficult task of tandem stance, soleus H-reflex gain is significantly decreased in both young and elderly adults.