Calibration of two objective measures of physical activity for children

Abstract

A calibration study was conducted to determine the threshold counts for two commonly used accelerometers, the ActiGraph and the Actical, to classify activities by intensity in children 5 to 8 years of age. Thirty-three children wore both accelerometers and a COSMED portable metabolic system during 15 min of rest and then performed up to nine different activities for 7 min each, on two separate days in the laboratory. Oxygen consumption was measured on a breath-by-breath basis, and accelerometer data were collected in 15-s epochs. Using receiver operating characteristic curve (ROC) analysis, cutpoints that maximised both sensitivity and specificity were determined for sedentary, moderate and vigorous activities. For both accelerometers, discrimination of sedentary behaviour was almost perfect, with the area under the ROC curve at or exceeding 0.98. For both the ActiGraph and Actical, the discrimination of moderate (0.85 and 0.86, respectively) and vigorous activity (0.83 and 0.86, respectively) was acceptable, but not as precise as for sedentary behaviour. This calibration study, using indirect calorimetry, suggests that the two accelerometers can be used to distinguish differing levels of physical activity intensity as well as inactivity among children 5 to 8 years of age.

Keywords:

• Children
• physical activity
• exercise
• accelerometer
• calibration

Acknowledgements

Support for this research project was provided by an unrestricted gift from the Gatorade Company for the Get Kids in Action Partnership with the University of North Carolina – Chapel Hill. The authors thank Dr. Anthony Hackney for use of the laboratory, Kathleen Shannon and Scott Gee for scheduling assistance, Fang Wen for help with the analysis, Dr. Leslie Bunce for reviewing the manuscript, and Marcus Bullett, Alex Johnson, Cheng-Feng Lin, Jennifer Reynolds, and Anna Sanzhar for help with data collection.