Classification of physical activity intensities using a wrist-worn accelerometer in 8–12-year-old children

Background: Population-specific accelerometer cut-points are required to accurately determine the accumulation of physical activity of various intensities.

Objectives: A calibration study was conducted (i) to determine the cut-points for the ActiGraph GT3X+, non-dominant, wrist-mounted accelerometer in children aged 8–12 years and (ii) to compare classification accuracies among the accelerometer’s three axes and vector magnitude (VM) values.

Methods: Forty-five children aged 8–12 years performed up to seven activities while wearing accelerometers on their non-dominant wrist. Activities were performed in a summer day camp setting, represented free-living activities, and lasted for 10 min with minutes 5–8.5 used for analysis. Direct observation and percentage of heart rate reserve were used to determine activity intensity.

Results: Receiver operator characteristic (ROC) analyses resulted in area under the curve values of all three axes and VM ranging 0.82–0.89, 0.80–0.83, 0.62–0.67 and 0.86–0.89 for light, moderate, vigorous and moderate-to-vigorous activity intensities. Additionally, regression analyses resulted in prediction equations with R2 values ranging from 0.70 to 0.77.

Conclusion: Results found comparable activity intensity classification accuracies from the ActiGraph GT3X+ wrist-worn accelerometer to previously published studies. Based on ROC and regression analyses, activity intensities can be distilled from this accelerometer using axis 1, axis 2 or VM values with similar classification accuracy.