Development of postural stability limits: Anteroposterior and mediolateral postural adjustment mechanisms do not...

There is increasing evidence that indicates a critical transition period for the maturation of postural control from the ages of 6-7 years. Some studies suggest that this transitional period may be explained by a change from a ballistic toward a sensory strategy, but the cause remains unknown. The purpose of this study was to investigate the influence of the transition period on dynamic postural control in a natural self-initiated leaning task under different sensory conditions. We evaluated the center of pressure (COP) displacement during maximum leaning in four directions (forward, backward, rightward, leftward) under three sensory conditions (eyes open, eyes closed and eyes closed standing on a foam). Three groups were tested: young children (4 years old), older children (8-10 years old) and adults (21-42 years old). The maximum COP excursion along the anteroposterior and mediolateral axes and the COP amplitude were analyzed. Young children showed smaller maximum anteroposterior and mediolateral COP excursion than other groups. Older children also exhibited a significantly smaller maximum excursion along the mediolateral direction but performed similar to adults along the anteroposterior direction. In a similar manner, the analysis of the COP amplitude did not indicate any differences between the groups along the anteroposterior axis. In contrast, along the mediolateral axis, the results showed developmental differences. Furthermore, the effect of sensory conditions was similar across the children's groups. Our results suggest an important plasticity period for the maturation of postural control mechanisms. Notably, our findings support the idea that the postural mechanisms controlling the anteroposterior axis reach maturity before the mechanisms involved in controlling the mediolateral axis.