Hiroki Aoki^1,, Shinichi Demura², Hiroshi Hirai³

This study examined how the amount of body sway various by age when people are standing on either a stable or an unstable surface with eyes either open or closed. The participants were 83 healthy women ranging in age from their teens to their eighties (with 9 to 12 women in each of the eight 10-year cohorts). Body sway was measured for 60 s while the participants were standing on a force plate with foam rubber (stable posture) or without form rubber (unstable posture). Path length (in cm), envelopment area (in cm2), and the ratio between these two measures were selected as evaluation parameters. In a three-way analysis of visual, posture, and age factors, path length, and envelopment area showed a significant interaction. Path length was shorter with the rubber than without it for all age levels with the eyes open or closed. An age-level difference was found only when the eyes were open. The envelopment area was smaller with than without the rubber with the eyes open for all age levels except women in their thirties and for all age groups with the eyes closed. Again, a significant age-level difference was found only with the eyes open. The ratio of length to envelopment area demonstrated a significant main effect for factors of both posture and age level. It was greater without than with the foam rubber with the eyes open for all age levels except women from their twenties to their forties, and for all age levels with the eyes closed. Coefficients in the linear regression equations, calculated based on the means for each age level, were significant in for three parameters. Values of path length and envelopment area were smaller without than with the rubber, but no significant differences were found between these values with the eyes open and closed. In conclusion, body sway in all age levels is greater on a less stable surface and increases with age, but the effect of vision on body sway can be disregarded.

aging, foam rubber, static balance