Slow anticipatory postural adjustments compromise dynamic stability in children with autism during gait initiation

Motor impairments are frequently observed in children with autism spectrum disorders (ASD). However, they remain absent from the DSM-5 diagnostic criteria, potentially delaying early ASD diagnosis. Gait initiation challenges balance–movement coordination more than steady-state motor tasks do and may offer valuable insights into distinctive motor profiles associated with ASD. Although few studies have explored locomotor initiation in children with ASD, they have not thoroughly analysed dynamic stability processes, leaving the underlying mechanisms of motor deficits in ASD unclear. This study compared the biomechanical characteristics of anticipatory postural adjustments (APAs) during gait initiation in children with ASD (n = 30) with those of age-matched non-autistic children (NAs) (n = 30). Three-dimensional ground reaction forces and whole-body marker trajectories were recorded via two force plates and an optoelectronic system. The APA duration, centre of pressure (CoP) features, margin of stability (MoS) at foot-off, and joint angles were computed and analysed. Intergroup differences were tested using nonparametric Mann–Whitney U tests. Compared with the NA children, the ASD children presented longer APA durations and reduced joint angles in the stance leg during the early APA subphase. These alterations resulted in a longer late-phase APAS duration and a significantly larger negative MoS in the mediolateral direction at foot-off. Overall, these findings suggest deficits in both feedforward control, as supported by a slower and more rigid strategy for initiation, and feedback regulation, as supported by a foot lift in worse conditions for dynamic stability. Together, these impairments may represent early motor markers of ASD with potential diagnostic value. • Children with autism spectrum disorder (ASD) often have motor difficulties not included in the main diagnostic criteria. • Studying these during gait initiation can reveal unique motor patterns. • 30 children with ASD and 30 non-autistic children were analysed during gait initiation • Children with ASD took longer to prepare for walking, had stiffer leg movements, and less stability. • Children with ASD may have trouble with feedforward and feedback control.