Anticipatory compensation of step-down perturbation is influenced by muscle force decrease

The altered gait patterns of adults with Down syndrome (DS) may contribute to their higher net metabolic rate (net-MR) during walking than adults without DS, leading to mobility limitations. This study examined the extent to which gait characteristics explain differences in net-MR during walking between adults with and without DS. Fifteen adults with DS (27 ± 8 years) and 15 adults without DS (28 ± 6 years) completed two testing sessions in which expiratory gases and kinematic data were collected, respectively, during treadmill walking. Participants walked at six, randomly-presented dimensionless speeds, ranging from slow to fast. Hierarchical and stepwise regressions were used to determine the proportion of the variance in net-MR explained by gait variables that differed between groups, after controlling for variance due to walking speed. Positive work rate, the range of the body center of mass (COM) mediolateral position and its square, variability in the time-course of COM anteroposterior velocity, and the variability of step length, step width, and step time significantly predicted net-MR (p < .05). These variables collectively explained 73.9% of the variance in net-MR that was explained by DS but not by walking speed. After accounting for shared variance among predictors, step length variability made the greatest unique contribution (10.6%) to the higher net-MR in adults with DS, followed by the range of COM mediolateral motion (6.3%), step width variability (2.8%), and variability in COM anteroposterior velocity (0.7%). Therefore, the gait characteristics of adults with DS appear to largely explain their higher net-MR during walking.