Validity and Reliability of the Wristband Activity Monitor in Free-living Children Aged 10-17 Years.

Objective: In this study we aimed to examine the reliability and validity of the wristband activity monitor against the accelerometer for children..

Methods: A total of 99 children (mean age = 13.0 ± 2.5 y) wore the two monitors in a free-living context for 7 days. Reliability was measured by intraclass correlation to evaluate consistency over time. Repeated-measures analyses of variance was used to detect differences across days. Spearman's correlation coefficient (rho), median of absolute percentage error, and Bland-Altman analyses were performed to assess the validity of the wristband against the ActiGraph accelerometer. The optimal number of repeated measures for the wristband was calculated by using the Spearman-Brown prophecy formula.

Results: The wristband had high reliability for all variables, although physical activity data were different across 7 days. A strong correlation for steps (rho: 0.72, P < 0.001), and moderate correlations for time spent on total physical activity (rho: 0.63, P < 0.001) and physical activity energy expenditure (rho: 0.57, P < 0.001) were observed between the wristband and the accelerometer. For different intensities of physical activity, weak to moderate correlations were found (rho: 0.38 to 0.55, P < 0.001).

Conclusion: The wristband activity monitor seems to be reliable and valid for measurement of overall children's physical activity, providing a feasible objective method of physical activity surveillance in children.