LAUSR

Abstract Purpose This study examined if the relationship between the rate of oxygen uptake (V̇O2) and output from hip-and wrist-worn accelerometers differs between adults with and without DS, and evaluated the accuracy of accelerometer output in estimating V̇O2. Materials and methods Sixteen adults with DS (10 men) and 19 adults without DS (10 men) performed 12 tasks including physical activities and sedentary behaviors. We measured V̇O2 with portable spirometry and accelerometer output (vector magnitude [VM]) with hip- and wrist-worn accelerometers. We used multi-level regressions to predict V̇O2 from VM, group, body mass index (BMI), age, height, weight, and sex. We evaluated prediction accuracy with absolute percent error and Bland-Altman plots. Results For both hip- and wrist-accelerometers, VM and group significantly predicted V̇O2 (p ≤ 0.021). When BMI was added, BMI was a significant predictor but group was not. The final models included VM and BMI (p ≤ 0.001; R 2 = 0.78 and 0.57, for hip and wrist accelerometer model, respectively). Absolute error was greater for the wrist- than the hip-accelerometer model (wrist: 37.9 ± 38.1%; hip: 22.5 ± 27.4%). Conclusions Adults with DS have different V̇O2 to VM responses, and this appears due to their higher BMI. Predictability of V̇O2 from accelerometer output is better for hip- than wrist-worn accelerometers. IMPLICATIONS FOR REHABILITATION Output from a triaxial accelerometer has high potential in predicting the energy expenditure and classifying the intensity of physical activity and sedentary behavior in adults with Down syndrome. Accuracy of predicting energy expenditure from accelerometer output is better for hip- than wrist-worn triaxial accelerometers. The development of appropriate rehabilitation interventions that include physical activity for improving health and function in adults with Down syndrome requires accurate assessments of physical activity levels.