Article

We examined (1) how sitting postural control in infants develops in the
anterior-posterior (A/P) and medial-lateral (M/L) directions of sway, and (2)
whether this control is already adult-like during the late phase of infant's
sitting acquisition. COP data were acquired from 14 healthy infants (from the
onset of sitting until independent sitting) and 21 healthy adults while sitting
on a force platform. Attractor dimensionality (CoD: correlation dimension),
attractor predictability (LyE: largest Lyapunov exponent), and sway variability
(RMS: root-mean square) were calculated from the COP data to evaluate postural
control. In the A/P direction, sitting was mastered by the infants by decreasing
the active degrees of freedom of the postural system (decreased CoD), using a
more predictable and (locally) stable sway (decreased LyE), and increasing sway
variability (increased RMS). Control of sitting became practically simple, stable
and exploratory with infant development. This may support the hypothesis that the
sitting posture serves as the foundation for the development of other motor
skills, as reaching. In the M/L direction, only sway variability decreased with
development, possibly due to changes in the infant's body dimensions. Taken
together, these findings indicate that early in development the focus is more in
the A/P than the M/L direction. Adults' postural control was found more adaptable
than the infants in both directions, involving more active degrees of freedom and
less predictable sway patterns. Identifying the factors that make the dynamics of
the postural system adult-like requires further research.
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Langue : ANGLAIS