Effects of ventilation on body sway during human standing.

Body sway was studied in standing with eyes closed during quiet breathing and apnoea. The hypothesis was that absence of ventilation improved balance. Performance and control of balance were assessed by centre of gravity and centre of pressure motions respectively. Eight healthy male subjects participated in the study. The analysis was performed for the first 20s when no activity of the diaphragm and no force variation at thoracic and abdominal levels were observed in apnoea condition. Performance and control were significantly improved in apnoea from 17 to 26% for the planar parameters; this improvement was only observed along the medio-lateral axis (around 34%), probably due to upper body asymmetry and diminution of the number of degrees of freedom that can be mobilised along this axis. In conclusion, ventilation in quiet breathing is a perturbing factor in human standing.