Associations of accelerometer-measured sedentary time, sedentary bouts, and physical activity with adiposity and fitness in children

ABSTRACT

Sedentary time (ST) has been inconsistently associated with adiposity and cardiorespiratory fitness in children in previous studies. We studied cross-sectional associations of ST, light physical activity (LPA), and moderate-to-vigorous physical activity (MVPA) with fat mass index (FMI) and cardiorespiratory fitness (estimated VO₂max). Associations were evaluated with and without considering pattern of ST by bout length. We measured ST and activity by a wrist-worn accelerometer, FMI by bioelectrical impedance, and VO₂max by Pacer test in 443 children (51.2% girls, 10.2 ± 0.6 years). Isotemporal substitution regression models estimated the effects of substituting ST, LPA, and MVPA on FMI and VO₂max. Further models repeated analyses separating ST into short (<10 min) and long (≥10 min) bouts. Only replacing ST or LPA with MVPA was consistently associated with lower FMI and greater VO₂max. When separated by bout length, only one unique association was found where replacing long ST bouts with short ST bouts was associated with lower FMI in girls only. In conclusion, activity pattern is associated with adiposity in girls and fitness in boys and girls. Separating ST into long and short ST bouts may be of minimal importance when assessing associations with adiposity and fitness using wrist-worn accelerometry in children.

KEYWORDS:

• Isotemporal substitution
• wrist accelerometry
• fat mass index
• VO₂max
• activity profile

Acknowledgments

MAJ, BBG, LS, and PMLS conceived the ideas for this paper, BBG and MJ carried out data analysis. HH, KB, PMLS and PS conducted data collection and entry for PEDALS. MAJ wrote the first draft under the supervision of BBG. All authors provided critical feedback and had final approval of submitted paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Heart Foundation of New Zealand [1618] for funding PEDALS University of Otago [ORG 0114-1015].