Postural Control Processes During Static and Dynamic Activities in Autism Spectrum Disorder

Abstract

Individuals with autism spectrum disorder (ASD) show multiple postural control deficits, including reduced postural stability during standing and reduced amplitude and frequency of anticipatory postural adjustments (APA) prior to planned movements. This study aims to identify mechanisms of postural control deficits in ASD during more challenging standing conditions including coordination of postural control processes used to support mediolateral (ML) and anteroposterior (AP) adjustments. We also examined APAs made during the initiation of walking to characterize predictive motor processes supporting postural control in ASD. Seventeen individuals with ASD were matched with 20 typically developing (TD) controls on age, gender ratio, nonverbal IQ, and body mass index (BMI). Participants completed three tests of postural control. During the first test, they stood with their feet shoulder width apart (neutral stance). During the second test, they stood with feet close together (Romberg one) in order to assess postural control during a more challenging standing condition in which the base of support is reduced. During the third test, participants stood with feet shoulder width apart and swayed their torso in a circle (circular sway). The standard deviation (SD) of their center of pressure (COP) in the ML and AP directions and the COP trajectory length were examined for each condition. We also assessed mutual information (MI), or the shared dependencies between COP in the ML and AP directions. Finally, individuals completed a step initiation task in which they took a step forward from one force platform to another. The APA amplitude and duration prior to stepping were measured, as were the maximum lateral sway during stepping, step distance, step velocity, and step duration. Individuals with ASD showed increased COP trajectory length relative to TD controls but no differences in COP SD during the standing tests. Compared to controls, participants with ASD showed greater levels of MI during static stance but reduced levels of MI during circular sway. During the step initiation task, groups did not differ on the amplitude or duration of APAs. During stepping, individuals with ASD showed reduced lateral sway, shorter step durations, and increased step velocity. Our finding that individuals with ASD show increased MI during circular sway suggests that they have a reduced ability to effectively coordinate distinct joint movements during dynamic postural adjustments. Our finding that individuals with ASD show reduced lateral sway when stepping suggests that motor rigidity may interfere with balance and gait in patients implicating basal ganglia circuits involved in guiding rapid or ballistic movements.