Prediction of oxygen uptake during over-ground walking in people with and without Down syndrome

The reduced gait stability and aerobic fitness of people with Down syndrome (DS) may increase their rate of gross oxygen uptake (gross-VO ₂) during over-ground walking. If so, the ACSM equation predicting gross-VO ₂ from speed may not be appropriate and an equation specifically for these individuals may be needed. This study therefore examined whether the relationship between gross- VO ₂ and speed differs between individuals with and without DS during over-ground walking and attempted to develop a gross-VO ₂ prediction equation for people with DS. Gross- VO ₂ was measured in 18 persons with DS (24.7 ± 6.8 years; 8 men) and 22 persons withoutDS(25.9 ± 4.8 years; 9 men) at rest and during five over-ground walking trials, each lasting 6 min, at 0.5, 0.75, 1.0, 1.25, and 1.5 m/s. Multi-level modeling with random intercepts and slopes demonstrated significant effects of speed, group, group-by-speed interaction, and speed squared (P<0.001). In each group, actual gross-VO ₂ did not differ from gross-VO ₂ predicted by the regression equation across speeds. Bland-Altman plots showed somewhat greater variability in the difference between actual and predicted gross-VO ₂ for participants with DS. Mean absolute error of prediction was 10.75 and 10.67% for participants with and without DS, respectively. In participants with DS, the ACSM formula under-estimated gross-VO ₂ across speeds, whereas, in participants without DS, only at 1.5 m/s (P<0.001). Therefore, individuals with DS show altered curvilinear gross-VO ₂ to speed relationship during over-ground walking. The present regression equation appears to offer accurate prediction in people with DS and could be used for prescribing over-ground walking intensities.