Non-linear development of postural control and strategy use in young children: a longitudinal study

This longitudinal analysis confirmed a nonmonotonic pattern of postural con trol development in children from age 5 to 8 years suggested by previous cr oss-sectional studies. Postural control was considered in terms of control strategy and its variability operationalized by mean and standard deviation of center of pressure (COP) velocity; and of effectiveness and its variabi lity operationalized by mean and standard deviation of COP anteroposterior (a-p) excursion. Periods of significant variability were used to indicate b ehavioral transitions. Seventeen healthy children (nine males, eight female s) aged 5-6 years (61.5-75 months) were tested at 3- to 4-month intervals u p to age 8 years (83-97 months) in eyes-open quiet stance on a force platfo rm for 30 s in each of ten trials. Data were reorganized into six developme ntal categories based on adjacent test dates prior to (-1) and after (+1, 2, +3, +4) a subject's trial with the lowest COP velocity (0). Developmenta l category is proposed to represent level of sensorimotor integrative skill . Within-subject ANCOVAs revealed a significant effect (P <0.0001) for deve lopmental category with covariance due to height, weight and actual age rem oved. Post hoe tests showed a significant effect (P <0.0001) on measures of strategy. However, differences in COP velocity (type of strategy used) and differences in its variability (denoting a transition between strategies) were not always coincident. Performance outcome (COP a-p excursion) changed near linearly across categories. It was concluded that a non-monotonic cha nge in control strategy as indicated by COP velocity describes the developm ent of quiet stance equilibrium. A transition occurs from a primarily open- loop to incorporation of open- and closed loop components of control. Honin g of strategy used precedes and follows transitions. Constriction of veloci ty and excursion may typify the early stages of bimodal strategy. Developme ntal categories describe affiliation with the strategy employed and may rep resent differentiable levels of sensorimotor integrative skill. They may be more useful in assessing progression of equilibrium control than consecuti ve age in years.