Uncontrolled manifold analysis of segmental angle variability during walking: preadolescents with and without Down syndrome

The uncontrolled manifold (UCM) approach allows us to address issues concerning the nature of variability. In this study we applied the UCM analysis to gait and to a population known for exhibiting high levels of performance variability, Down syndrome (DS). We wanted to determine if preadolescents (ages between 8 and 10) with DS partition goal-equivalent variability (UCM parallel to) and non-goal equivalent variability differently than peers with typical development (TD) and whether treadmill practice would result in utilizing greater amounts of functional, task-specific variability to accomplish the task goal. We also wanted to determine how variance is structured with respect to two important performance variables: center of mass (COM) and head trajectory at one specific event (i.e., heel contact) for both groups during gait. Preadolescents with and without DS walked on a treadmill below, at, and above their preferred overground speed. We tested both groups before and after four visits of treadmill practice. We found that children with DS partition more UCM parallel to variance than children with TD across all speeds and both pre and post practice. The results also suggest that more segmental configuration variance was structured such that less motion of COM than head position was exhibited at heel contact. Overall, we believe children with DS are employing a different control strategy to compensate for their inherent limitations by exploiting that variability that corresponds to successfully performing the task.