PUYAU, MAURICE R., ANNE L. ADOLPH, FIROZ A. VOHRA, AND NANCY F. BUTTE. Validation and calibration of physical activity monitors in children. Obes Res. 2002;10:150 -157. Objective: This study was designed to validate accelerometer-based activity monitors against energy expenditure (EE) in children; to compare monitor placement sites; to field-test the monitors; and to establish sedentary, light, moderate, and vigorous threshold counts. Research Methods and Procedures:Computer Science and Applications Actigraph (CSA) and Mini-Mitter Actiwatch (MM) monitors, on the hip or lower leg, were validated and calibrated against 6-hour EE measurements by room respiration calorimetry, activity by microwave detector, and heart rate by telemetry in 26 children, 6 to 16 years old. During the 6 hours, the children performed structured activities, including resting metabolic rate (RMR), Nintendo, arts and crafts, aerobic warm-up, Tae Bo, treadmill walking and running, and games. Activity energy expenditure (AEE) computed as EE Ϫ RMR was regressed against counts to derive threshold counts. Results: The mean correlations between EE or AEE and counts were slightly higher for MM-hip (r ϭ 0.78 Ϯ 0.06) and MM-leg (r ϭ 0.80 Ϯ 0.05) than CSA-hip (r ϭ 0.66 Ϯ 0.08) and CSA-leg (r ϭ 0.73 Ϯ 0.07). CSA and MM performed similarly on the hip (inter-instrument r ϭ 0.88) and on the lower leg (inter-instrument r ϭ 0.89). Threshold counts for the CSA-hip were Ͻ800, Ͻ3200, Ͻ8200, and Ն8200 for sedentary, light, moderate, and vigorous categories, respectively. For the MM-hip, the threshold counts were Ͻ100, Ͻ900, Ͻ2200, and Ն2200, respectively. Discussion: The validation of the CSA and MM monitors against AEE and their calibration for sedentary, light, moderate, and vigorous thresholds certify these monitors as valid, useful devices for the assessment of physical activity in children.

Purpose Accurate, nonintrusive and feasible methods are needed to predict energy expenditure (EE) and physical activity (PA) levels in preschoolers. Herein, we validated cross-sectional time series (CSTS) and multivariate adaptive regression splines (MARS) models based on accelerometry and heart rate (HR) for prediction of EE using room calorimetry and doubly labeled water (DLW), and established accelerometry cut-points for PA levels. Methods Fifty preschoolers, mean±SD age 4.5±0.8 y, participated in room calorimetry for minute-by-minute measurements of EE, accelerometer counts (AC) (Actiheart and ActiGraph GT3X+) and HR (Actiheart). Free-living, 105 children, aged 4.6±0.9 years, completed the 7-d DLW procedure while wearing the devices. AC cut-points for PA levels were established using smoothing splines and receiver operating characteristic curves. Results Based on calorimetry, mean percent errors for EE were -2.9±10.8% and -1.1±7.4% for CSTS models, and -1.9±9.6 and 1.3±8.1% for MARS models using the Actiheart and ActiGraph+HR devices, respectively. Based on DLW, mean percent errors were -0.5±9.7% and 4.1±8.5% for CSTS models and 3.2±10.1% and 7.5±10.0% for MARS models using the Actiheart and ActiGraph+HR devices, respectively. Applying activity EE thresholds, final accelerometer cut-points were determined: 41, 449, and 1,297 cpm for Actiheart x-axis; 820, 3,908, and 6,112 cpm for ActiGraph vector magnitude; and 240, 2,120, and 4,450 cpm for ActiGraph x-axis for sedentary/light, light/moderate, and moderate/vigorous PA (MVPA). Based on confusion matrices, correctly classified rates were 81–83% for sedentary PA, 58–64% for light PA and 62–73% for MVPA. Conclusion The lack of bias and acceptable limits of agreement affirm the validity of the CSTS and MARS models for the prediction of EE in preschool-aged children. Accelerometer cut-points are satisfactory for classification of sedentary, light and moderate-vigorous levels of PA in preschoolers.

Efforts should be made to shift the time in sedentary activity to light activity, and to increase the time spent in moderate to vigorous activity in U.S. Hispanic children and adolescents, with special attention given to the overweight, girls, and adolescents.

Uniaxial and triaxial accelerometers are acceptable devices with similar classification accuracy for sedentary, light, and moderate-to-vigorous levels of PA in preschoolers.