Age-related complexity and coupling of children's sitting posture

This study tested the hypothesis that postural complexity increases as the coupling across the axes of motion decreases as children get older. Children aged 6 and 10 years and young adults (18-23 years) were seated on a wooden box placed atop a force platform that recorded their mediolateral and anteroposterior center of pressure (COP) motion with their feet supported and unsupported. The COP path length and complexity decreased with age, and this was paralleled by an increase in relative phase entropy across the axes of sway motion. The postural sway of the younger children was dominated by slower fluctuations that were more tightly coupled across the axes of motion than the adults. The findings support the postulation that the development of children's sitting posture is characterized by increased freedom in postural coordination that realizes a more loosely coupled but adaptive postural motion with a reduced amount of sway.