Effects of 20 days horizontal bed rest on maintaining upright standing posture in young persons.

: The effects of 20 days horizontal bed rest (BR) on postural reflex were studied by measuring fluctuation of center of gravity in the body during two legs or one leg upright standing in 10 young volunteers. The fluctuation was decided as total moving distance of the center recorded during 60sec standing on a force plate. The stability was measured by the moved area. After BR, the moving distance increased during two legs standing with open eyes (p<0.05), but statistically unchanged with closed eyes. The moving area decreased during right one-leg standing with closed eyes (p<0.05), but unchanged during left one-leg standing. Despite with open eyes the increased distance suggested that postural reflexes to maintain upright position were probably decreased by increased unsuitable feedback informations from the visual receptor deconditioning during BR. The decreased area during right one-leg standing with closed eyes also suggested that the declined standing posture reflex was probably related to more rapidly lowered functions for maintaining standing position in the dominating leg than in the other.