Test-retest reliability of motion capture technology for assessing balance in children with autism spectrum disorder.

BACKGROUND: Children with autism spectrum disorder (ASD) often show balance impairments that may affect motor development. Portable motion capture may provide quantitative balance indices, but its test-retest reliability in pediatric ASD remains unclear. RESEARCH QUESTION: This study evaluated seven-day test-retest reliability of a portable marker-based motion capture system for head-sway-derived balance indices in children with ASD and described exploratory unadjusted differences from typically developing (TD) children. METHODS: Twenty-two children (11 ASD, 11 TD) completed long-sitting, eyes-open standing, and eyes-closed standing balance tests using head-mounted reflective markers. Outcomes were mediolateral sway amplitude (Dx), anteroposterior sway amplitude (Dy), and 95% confidence ellipse area (Area). Reliability was assessed using intraclass correlation coefficients, standard error of measurement, and Bland-Altman plots. Between-group analyses were exploratory because the groups were not matched by age or sex. RESULTS: In children with ASD, Dy showed good reliability (ICC = 0.77-0.87; SEM = 1.98-3.19), with the highest reliability in long sitting (ICC = 0.87). Dx showed poor to moderate reliability (ICC = 0.45-0.69), and Area showed moderate to good reliability (ICC = 0.65-0.77). Exploratory comparisons showed larger sway values in the ASD group, but these results may reflect baseline age and sex differences. SIGNIFICANCE: The system reproducibly measured anteroposterior head-sway in children with ASD, particularly in long sitting. Further validation against reference balance measures and larger age- and sex-matched studies is needed before diagnostic or discriminative use.