WRIST ACCELEROMETER CUT-POINTS FOR MEASURING PHYSICAL ACTIVITY AND SEDENTARY BEHAVIOR IN ADULTS WITH DOWN SYNDROME

Morgan Bailey, Brantley K. Ballenger, Maggie Chamberlain, Stamatis Agiovlasitis, FACSM. Mississippi State University, Mississippi State, MS. BACKGROUND: The wrist may be an appropriate site for accelerometer placement for adults with Down syndrome (DS) because it may increase compliance. However, wrist accelerometer output has not been calibrated in adults with DS. This study therefore aimed to develop wrist worn accelerometer cut-points for sedentary behavior and moderate and vigorous physical activity for adults with DS. METHODS: Twenty-three adults with DS (11 men & 12 women; age 34 ± 8 years) performed 18 tasks each lasting 6 min: lying; sitting; watching a movie; playing app on tablet; drawing; standing; folding clothes; vacuuming; sweeping; moving a box; basketball; soccer; fitness circuit; dancing; walking at the preferred speed and at 0.8 and 1.4 m.s-1; and running. Rate of oxygen uptake was measured with portable indirect calorimetry (K5, Cosmed) and expressed as Metabolic Equivalents (METs). Vector Magnitude was determined based on output from a triaxial accelerometer (wGT3X-BT, Actigraph) worn on the non-dominant wrist. Vector Magnitude cut-points for sedentary behavior and moderate (3.0 - 5.99 METs) and vigorous (≥6 METs) physical activity were determined using Receiver Operating Characteristic (ROC) curves. Area under the ROC curve was used to evaluate overall classification performance of the models. Optimal cut-points maximizing sensitivity and specificity were selected based on Youden’s index. RESULTS: Area under the ROC curve was high for all models: (a) sedentary behavior (0.95; 95% CI: 0.93 - 0.97); (b) moderate physical activity (0.86; 95% CI: 0.82 - 0.89); and (c) vigorous physical activity (0.91; 95% CI: 0.84 - 0.97). The optimal Vector Magnitude cut-points were: (a) sedentary behavior ≤2680 counts∙min-1 (sensitivity 0.97; specificity 0.87; Youden’s index 0.84); (b) moderate physical activity ≤5013 counts∙min-1 (sensitivity 0.81; specificity 0.78; Youden’s index 0.59); and (c) vigorous physical activity ≥5458 counts∙min-1 (sensitivity 1.00; specificity 0.66; Youden’s index 0.66). CONCLUSION: This study offers DS-specific wrist-based accelerometer cut-points for classifying sedentary behavior and physical activity intensity in adults with DS. The cut-points appear to have high accuracy. Use of DS-specific cut-points may advance the study of physical activity and sedentary behavior in adults with DS. Funding: NIH Grant R15HD09866