Development of the upright postural sway of children.

From 1988 to 1992, 1188 children (576 boys and 612 girls) three to 11 years old were studied using the Stasio-analyzer to clarify developmental change of upright postural sway. Developmental change in the contact surface area of the sole, the coefficient of variation for the contact surface area, total sway area, total sway path and position of the centre of gravity were analysed. The contact surface area increased markedly between the ages of three to five and of seven to nine years, and increased slightly between six and seven years. Age six to seven years is proposed as a turning point of plantar arch formation as regards change in the contact surface area of the sole. Upright postural sway decreased markedly between the ages of three to five years and then slowly after age six. Boys under ten years swayed more than girls. The centre of gravity of the foot in children standing upright shifted towards the toes with increasing age: its distance from the heel was about 36 per cent of the foot length at age three to five years and 42 per cent at 11 years.