Children achieve adult-like sensory integration during stance at 12-years-old

Abstract

This study examined balance control in children to determine at what age the integration of sensory information in unperturbed stance is comparable to that of adults. In addition, it examined whether overall performance was related to age, gender and specific physical characteristics, such as height, weight and body mass index (BMI). Seventy-four female and 80 male children between the ages of 6 and 12 years participated in the study, as well as 20 adults, aged 20–22 years. The Sensory Organization Test (SOT), a component of computerized dynamic posturography, was used to assess overall balance as well as the use of specific sensory information in maintaining stability. Analyses of variance revealed significant differences between equilibrium scores of 7- and 8-year-old and 11- and 12-year-old (p < .01), with only the 12-year-old participants achieving scores comparable to those of the adult group. A repeated-measures analysis of variance comparing the use of different sensory information across age and gender groups revealed that while all groups demonstrated mature use of somatosensory information, children under 11 did not use visual information as effectively as adults, and only the 12-year-old group demonstrated adult-like use of vestibular information. Correlational analyses revealed a moderate correlation between composite balance scores and age, r(152) = .38, p < .001, but poor correlations between the composite equilibrium score and height, weight and BMI (r < .13, p > .15). Multiple regression analysis revealed that while physical characteristics accounted for approximately 20% of the variability in the composite equilibrium score, age alone accounted for the largest single contribution to the variance (16%). These results support recent findings suggesting that children do not demonstrate adult-like use of sensory information prior to age 12 years.

Introduction

The nature of the development of postural control has intrigued researchers for many years. A better understanding of balance and how and why postural control develops is important for many reasons. This knowledge would enable earlier detection of atypical postural development in children, provide better understanding and appreciation of the differences seen between individual and groups of children, and might also lead to improved interventions for children and adults with pathological balance impairments.

Postural control is a broad term used to describe a complex mixture of various abilities. Adequate postural control requires not only the ability to maintain quiet stance, but also the ability to maintain stability when perturbed or when actively moving a limb or the entire body, such as when reaching or when walking [1]. In order to coordinate the forces required for these tasks, an individual also must be able to organize sensory information, including visual, somatosensory and vestibular information.

The different components of postural control have been studied extensively in children. Hayes and Riach [2] assessed quiet stance in children aged 2–14 years and found that amplitude of postural sway decreased with age, as did the variability of postural responses. Taguchi and Tada [3] reported that spontaneous sway during quiet stance was comparable to that of adults in children aged 9–12 with eyes open. Several studies have been conducted to assess compensatory postural control to perturbations to balance [4], [5], [6]. In general, these studies documented that children exhibited well-organized muscular responses to perturbations by 7–10 years of age, although the amplitude, latency and duration of the responses were greater than those of the adults.

Investigators have also examined how children use sensory information. Initial studies were conducted using a “moving room” in which the responses of sitting and standing infants and children were observed as the walls around them moved [7], [8]. These methods were later replaced by computerized dynamic posturography (CDP). CDP is a tool used to assess the sensory and motor components of postural control, and includes different testing protocols, including the Sensory Organization Test (SOT), Motor Control Test (MCT) and the Adaptation Test (ADT) [9]. The Sensory Organization Test assesses use of sensory information by measuring postural sway during quiet stance while systematically manipulating sensory input, such as by eliminating visual input or by distorting somatosensory or visual information by sway-referencing the platform or visual surround. The method of sway-referencing involves tilting the platform or visual surround in an anterior–posterior direction in response to the individual's center of pressure movement in the anterior–posterior direction [9]. Sway-referencing provides inaccurate sensory input to the visual and somatosensory systems, enabling assessment of vestibular function and determination of how the three sensory inputs are weighted by the individual.

Using procedures similar to the SOT, Shumway-Cook and Woollacott [6] reported data that has for several years served as the standard timeline for postural development for educators, clinicians and researchers alike. After assessing 21 children ranging in age from 15 months to 10 years, they determined that children in the 7–10 years age group demonstrated mature postural control as evident by the presence of adult-like response synergies and the ability to resolve sensory conflict. Children younger than 7 years were unable to balance effectively when input from both the visual system and the somatosensory system was removed or altered.

In recent years, however, several studies have demonstrated that mature responses do not appear until much later in childhood or adolescence. Peterka and Black [10], in their investigation of 214 individuals ranging in age from 7 to 81 years, found that children younger than age 15 years demonstrated increased postural sway compared to adults when all sensory information was available and accurate. This sway was more pronounced in conditions of altered somatosensory cues. In their study of 112 Japanese children, Hirabayashi and Iwasaki [11] proposed that generalized postural stability had not reached adult level by age 15 years, nor had vestibular function for resolving sensory conflict. Three years later, Rine et al. [12] reported similar findings in that the oldest children in their study (age 7.5 years) swayed more than the adults, and scores measuring visual and vestibular function were significantly lower, as well.

While significant research has been done to study the timeline of postural control development, there is limited scientific evidence of physiological changes that lead to adult-like postural control in children. Immaturity of the sensory systems would seem a logical explanation for the differences seen between children and adults. However, from a physiological standpoint, the visual and vestibular systems are largely mature well before balance performance is adult-like. The components of the vestibular system, including the semicircular canals, otolith organs and the degree of myelination of the vestibular nerve are reported to be equivalent to those of adults at birth [13], [14]. The degree of maturity of the visual system is more variable. While binocular vision is mature by 4–5 months of age and stereoacuity adult-like by 6–7 months [15], myelination of the visual pathway is not complete until around 2 years, and the retina is not mature until at least age 4 years [16]. This relative maturity of the sensory systems suggests that differences in postural control between children and adults are most likely attributable to other factors, such as processing or integration of visual, vestibular and somatosensory information.

In further efforts to explain the nature of postural control development, researchers have begun to investigate the influence of anthropometric characteristics, such as height, weight and body mass index (BMI) in addition to previously studied factors of chronological age and gender. Lebiedowska and Szcyewska [17] investigated the roles played by age, gender, body height and body mass on ability to maintain static stance for children aged 7–18 years. They found no difference for any of the variables between males (n = 25) and females (n = 32) in their sample. Furthermore, they reported no correlation between sway parameters (total path, length of sway sagitally and laterally, and velocity) and anthropometric characteristics when children were asked to maintain static stance with or without visual feedback, and only weak correlations negative correlations between age and sway parameters when children were given feedback [17]. In a similar study of postural sway with static stance, Odenrick and Sandstedt found greater sway amplitude in males (n = 11) than females under age 10 years (n = 10) [18]. Height and weight were not related to sway in females, and explained only 20% of the variability of sway in males.

As childhood obesity becomes more of a problem, with 15% of children between the ages of 6 and 19 years reporting a (BMI) at or above the 95th percentile [19], researchers have begun to question whether children with higher body mass indices mature from a postural control standpoint differently than children with lower body mass indices Currently, this relationship remains unclear. In their investigation of gait and postural stability in boys aged 8–10 years, McGraw et al. [20] reported greater sway in both the anterior–posterior and medial–lateral directions in obese boys (n = 10) as compared to age-matched non-obese boys (n = 10). These differences were greatest during conditions in which vision was absent or altered and when both vision and the base of support were changed. Non-obese boys demonstrated increased sway only during trials in which both vision and the base of support were altered. In contrast, Goulding et al. [21] found no significant differences between Equitest SOT scores or BalanceMaster limits of stability (LOS) scores for their sample of 25 overweight boys and 68 boys with healthy BMI, all aged 10–21 years.

Overall, there is a lack of consensus regarding the influence of age, gender and anthropometric characteristics on the development of postural control. Because the nature of this development remains largely undetermined, further study of the roles played by these variables is warranted. The objectives of the current study were to determine at what age children's postural sway in quiet stance, as well as their ability to use sensory information to maintain balance during unperturbed standing was comparable to adults’ abilities, and to what extent physical characteristics, such as gender, height, weight and body mass index influenced these abilities.