The use of the intensity gradient and average acceleration metrics to explore associations with BMI z-score in children

ABSTRACT

This study used the intensity gradient (IG) and average acceleration metrics to describe children’s activity profiles and explore associations with body mass index (BMI) z-score. Two hundred and forty-six children (n = 138 girls) aged 9.6 ± 1.4 years wore a wrist-mounted ActiGraph wGT3X-BT accelerometer for 7 days on their non-dominant wrist. Physical activity (PA) metrics captured included: the IG which describes the intensity distribution of accelerations across the 24 h monitoring period; average acceleration which provides a measure of the volume of activity; total moderate-to-vigorous PA (MVPA) and inactive time. Acceleration was averaged over 5s epochs. Finally, BMI z-score was calculated for each participant. Average acceleration was negatively associated with BMI z-score (p < 0.05) independent of age and gender but not IG. The IG was negatively associated with BMI z-score independent of potential correlates and average acceleration. Total MVPA was not associated with BMI-z score. The IG and average acceleration metrics may be used to explore the independent or cumulative effects of the volume and intensity distribution of activity upon measures of health and well-being in children to inform specific activity recommendations.

KEYWORDS:

• ActiGraph
• accelerometer
• activity metrics
• wrist-worn
• raw acceleration

Acknowledgments

The authors would like to thank the children, schools, teachers and parents who agreed to participate in this study. This study was funded by The University of the West of Scotland, VP Research Fund. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors’ Contributions

GMcL and SD collected all of the data: DSB performed the statistical analysis and drafted the manuscript; DSB conceived, designed and coordinated the study and wrote the manuscript. RA helped to coordinate the study and reviewed the draft manuscript. All authors have read and approved the final version of the manuscript and agree with the order of authors.

None of the authors declare competing financial interests.

Disclosure of interest

The authors report no conflict of interest.