Maggie Chamberlain, Brantley K. Ballenger, Morgan Bailey, Stamatis Agiovlasitis, FACSM. Mississippi State University, Mississippi State, MS.

BACKGROUND: Accelerometer cut points based on 3 and 6 Metabolic Equivalents (METs) for moderate and vigorous physical activity (PA) may not be appropriate for adults with Down syndrome (DS). PA intensity may be better reflected in the oxygen uptake reserve (%VO2R) which can account for the low aerobic fitness and resting metabolic rate of adults with DS. This study examined if accelerometer cut points for moderate and vigorous PA differ between the METs and %VO2R approaches to PA intensity in adults with DS. METHODS: Twenty-three adults with DS (age 34±8 years; 11 men) performed 18 tasks of varying intensity each lasting 6 min. Aerobic fitness was estimated with a submaximal treadmill test. The rate of oxygen uptake during the treadmill test and the 18 tasks was measured with breath-by-breath portable calorimetry. PA intensity during the tasks was expressed as METs (moderate: 3.0-5.99 METs; vigorous ≥6 METs) and %VO2R (moderate: 40.0-59.9%; vigorous: ≥60%). PA was measured with a triaxial accelerometer (wGT3X-BT, Actigraph) on the non-dominant hip, and the Vector Magnitude (VM) was used in analysis. Receiver Operating Characteristic (ROC) curves were used to identify VM cut points for moderate and vigorous PA using METs and %VO2R. Overall classification performance was assessed with the area under the ROC curve. Optimal cut points maximizing sensitivity and specificity were selected using Youden’s index. RESULTS: Area under the ROC curve was high for all models; for METs: (a) moderate (0.89; 95%CI: 0.85-0.92) and (b) vigorous (0.91; 95%CI: 0.86-0.96); for %VO2R: (a) moderate (0.88; 95%CI: 0.84-0.91) and (b) vigorous (0.86; 95%CI: 0.82-0.90). The optimal VM cut points based on METs were: (a) moderate ≥2863 counts∙min-1 (sensitivity 0.87; specificity 0.77; Youden’s index 0.64); and (b) vigorous ≥3698 counts∙min-1 (sensitivity 1.00; specificity 0.74; Youden’s index 0.74). VM cut points based on %VO2R were: (a) moderate ≥2056 counts∙min-1 (sensitivity 0.99; specificity 0.68; Youden’s index 0.67); and (b) vigorous ≥3698 counts∙min-1 (sensitivity 0.77; specificity 0.80; Youden’s index 0.57). CONCLUSION: Moderate intensity PA cut-points were higher when based on METs than %VO2R. Vigorous intensity PA cut-points did not differ between methods. Utilizing cut-points based on %VO2R may more accurately express levels of moderate PA in adults with DS. Funding: NIH Grant R15HD098660

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