Hip And Wrist Accelerometer Cut-points For Adults With Down Syndrome

Adults with Down syndrome (DS) have very low aerobic fitness. Accelerometer cut-points for moderate and vigorous physical activity (PA) may thus be more appropriate if developed based on the oxygen uptake reserve (%VO2R) which accounts for aerobic fitness. PURPOSE: To develop cut-points for moderate and vigorous PA for adults with DS based on %VO2R from hip and wrist accelerometer output. METHODS: Forty-one adults with DS (19 women; age 35 ± 9 years) performed 17 tasks for 6 min each: sitting; standing; walking over-ground at 3 speeds; running; watching movie; playing app; drawing; folding clothes; vacuuming; sweeping; moving a box; basketball; soccer; fitness circuit; and dancing. Aerobic fitness was estimated with a submaximal treadmill test. Oxygen uptake was measured with breath-by-breath open-circuit spirometry (K5, Cosmed) and expressed as %VO2R. Output from hip and wrist accelerometers (wGT3X-BT, Actigraph) was determined as Vector Magnitude (VM). VM cut-points for moderate and vigorous PA were identified with Receiver Operating Characteristic (ROC) curves based on %VO2R of 40.0 - 59.9% and ≥ 60%, respectively. Optimal cut-points for moderate and vigorous PA that maximized sensitivity, specificity and Youden’s index (YI) were selected. RESULTS: Area Under the ROC Curve (AUC) and Gini Index (GI) were high for all models; for the hip accelerometer: (a) moderate intensity PA (AUC 0.87 95% CI: 0.85 - 0.90; GI 0.74;) and (b) vigorous intensity PA (AUC 0.86; 95% CI: 0.83 - 0.90; GI 0.72;); and for the wrist accelerometer: (a) moderate intensity PA (AUC 0.84; 95% CI: 0.81 - 0.86; GI 0.67;) and (b) vigorous intensity PA (AUC 0.85; 95% CI: 0.81 - 0.88; GI 0.70). The optimal VM cut-points for the hip accelerometer were: (a) moderate PA ≥2065 counts·min-1 (sensitivity 0.97; specificity 0.70; YI 0.66); and (b) vigorous PA ≥3353 counts·min-1 (sensitivity 0.85; specificity 0.72; YI 0.57). VM cut-points based on the wrist accelerometer were: (a) moderate PA ≥3803 counts·min-1 (sensitivity 0.87; specificity 0.66; YI 0.53); and (b) vigorous PA ≥6639 counts·min-1 (sensitivity 0.72; specificity 0.80; YI 0.52). CONCLUSION: Hip and wrist accelerometer cut-points for PA intensity based on %VO2R appear accurate and, if utilized, may improve PA assessment in adults with DS. Funding: NIH R15HD098660 Supported by: NIH R15HD098660