Abstract
The purpose of this study was to investigate the effects of weight bearing conditions using static tilt condition and additional weight load on the soleus H-reflex in humans. Eight healthy subjects were tilted from the supine position to the standing position. In addition, they kept upright standing without and with a weight load of 50% of the body weight. No background activities in the muscle or changes in the recruitment profiles were observed. The effect was −9.1(95%C. I. : −15.1 to −3.1)%Mmax under the static tilt condition, and −1.9(−4.8 to 1.0)%Mmax under the additional weight load condition. The effect under the static tilt condition positively related to the effect under the additional weight load condition. It is suggested that weight bearing-induced proprioceptive input and tonic vestibular input increase presynaptic inhibition of soleus Ia afferents during upright standing in humans.
