Transitioning from the level surface to stairs in children with and without Down syndrome: Motor strategy and anticipatory locomotor adjustments

•Children with DS choose a more conservative strategy to safely ascend the stairs.•Children with DS decrease step length and velocity for last four approaching steps.•Children with DS decrease vertical toe clearance for last four approaching steps.•Children with DS decrease horizontal toe velocity for last four approaching steps.•Ankle load affects children with DS more in motor strategy and locomotor pattern. Children with Down syndrome (DS) show underdeveloped motor strategy and anticipatory locomotor adjustments (ALA) before crossing an obstacle. Stairs presents another important setting to study environment navigation and motor adaptation. Inclusion of external ankle load is often used to perturb the stability of a system and observe the emergence of new patterns. How do stair height and external ankle load affect motor strategy and ALA in 5-to-11-year-old children with typical development (TD) and with DS when approaching the stairs? Fourteen children with DS and 14 age- and sex-matched children with TD participated in the study. They walked along a 5-meter walkway and ascended 3-step staircases. There were three staircases (low, moderate, and high heights) and 2 loading conditions (no load and ankle load). A 3D motion capture system was used to collect data. Motor strategy was coded for each trial. Step length, width, time, and velocity, minimum toe clearance, and horizontal toe velocity were calculated for the last four steps before stair ascent. Mixed ANOVAs with repeated measures were conducted for statistical analysis. The TD group walked up all the stairs, while the DS group displayed a strategy shift from walking to crawling when the stairs became higher. While the TD group maintained the values of most spatiotemporal variables, the DS group continuously decreased step length and velocity but not step width over the last four approaching steps. Ankle load decreased step length, step velocity, minimum toe clearance, and horizontal toe velocity in the DS group, to a greater extent, than in the TD group. Children with DS show underdeveloped motor strategy and ALA when approaching the stairs, and external ankle load further disrupts these patterns. Stair negotiation appears to be an effective assessment tool for evaluating motor adaptation in children with DS.