Validation and Calibration of an Accelerometer in Preschool Children

The following fundamental research was not performed explicitly using an ActiGraph device. However, the theories developed in this paper are used extensively in ActiGraph’s ActiLife software.

Objective Obesity rates in young children are increasing, and decreased physical activity is likely to be a major contributor to this trend. Studies of physical activity in young children are limited by the lack of valid and acceptable measures. The purpose of this study was to calibrate and validate the ActiGraph accelerometer for use with 3- to 5-year-old children.

Research Methods and Procedures Thirty preschool children wore an ActiGraph accelerometer (ActiGraph, Fort Walton Beach, FL) and a Cosmed portable metabolic system (Cosmed, Rome, Italy) during a period of rest and while performing three structured physical activities in a laboratory setting. Expired respiratory gases were collected, and oxygen consumption was measured on a breath-by-breath basis. Accelerometer data were collected at 15-second intervals. For cross-validation, the same children wore the same instruments while participating in unstructured indoor and outdoor activities for 20 minutes each at their preschool.

Results In calibrating the accelerometer, the correlation between VO₂ (ml/kg per min) and counts was r = 0.82 across all activities. The only significant variable in the prediction equation was accelerometer counts (R2 = 0.90, standard error of the estimate = 4.70). In the cross-validation, the intraclass correlation coefficient between measured and predicted VO₂ was R = 0.57 and the Spearman correlation coefficient was R = 0.66 (p < 0.001). Cut-off points for moderate- and vigorous-intensity physical activity were identified at 420 counts/15 s (VO₂ = 20 mL/kg per min) and 842 counts/15 s (VO₂ = 30 mL/kg per min), respectively. When these cutpoints were applied to the cross-validation data, percentage agreement, kappa, and modified kappa for moderate activity were 0.69, 0.36, and 0.38, respectively. For vigorous activity, the same measures were 0.81, 0.13, and 0.62.

Discussion Accelerometer counts were highly correlated with VO₂ in young children. Accelerometers can be appropriately used as a measure of physical activity in this population.

Key words physical activity, measurement, count cutpoints, indirect calorimetry, ActiGraph

Original web location: http://www.ncbi.nlm.nih.gov/pubmed/17135617