Standing Balance on Rigid and Unstable Surfaces in Children on the Autism Spectrum: Interaction Between Symptom and Motor Domains
Difficulty with postural stability during standing on stable surfaces has been reported in people on the autism spectrum (see Memari et al.  for review). However, it is unclear whether unstable surfaces may present even more of a challenge to youth with autism spectrum disorder (ASD). Because much of the ground on which we balance has the potential to be unstable, it is important to understand standing balance on both rigid and unstable surfaces. Further, it is important to understand individual differences that might relate to more severe postural stability challenges in ASD.
1) To examine postural stability in youth on the autism spectrum compared to youth with typical development during standing on a traditional rigid platform compared to a tiltable platform, and 2) to examine whether postural stability measures are related to individual variation in social communication and repetitive behavior symptom severity.
Twenty youth on the autism spectrum and 18 youth with typical development (ages 6-16 years, IQ>70, 89% male) stood on both a rigid and tiltable platform that recorded force and center of pressure. Postural sway area and total mean velocity were calculated and served as the primary measures of postural stability. Postural stability was then examined as a correlate of autism symptom severity (RBS-R, SCQ, and SRS). To determine if individuals with ASD exhibited poorer postural stability than individuals with typical development on a rigid versus unstable platform, we conducted a linear mixed-effects analysis to examine the effect of surface condition (rigid versus unstable surface), group status (ASD versus typical development), and FSIQ on postural stability, after controlling for age and repeated measures. Partial spearman rank correlations (regressing out the effects of age) were used to examine the relation between postural stability and autism/autism-like symptom severity.
There was a main effect for surface, p < .001, but not for group status, p = .86. Contrary to our hypotheses, there was not a significant surface-by-group interaction, p = .65. However, there was a significant three-way interaction between group, surface condition and FSIQ, p<0.05. This interaction suggests that those in the ASD group with lower FSIQ had the most difficulty with the unstable surface compared to the rigid surface. FSIQ was not associated with postural sway area in the typically developing group under either surface condition.
ASD diagnosis alone was not predictive of greater balance challenge on the unstable surface. Instead, only youth on the autism spectrum with lower IQs exhibited differentially more balance challenge on the unstable surface. These results suggest that balance challenge may be related to more severe autism and autism-like symptoms. Further, unstable surfaces, which are common in day-to-day life, may present a particular challenge to the balance of individuals on the autism spectrum with more severe symptom profiles.
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