Cross-Sectional and Longitudinal Associations between Non-School Time Physical Activity, Sedentary Time, and Adiposity among Boys and Girls: An Isotemporal Substitution Approach

• Main Authors: Kelsey L. McAlister, Jennifer Zink, Daniel Chu, Britni R. Belcher, Genevieve F. Dunton
• Format: Article
• Language: English
• Published: MDPI AG 2021-04-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: reallocation; obesity; youth; sex differences; accelerometry
• Online Access: https://www.mdpi.com/1660-4601/18/9/4671
• ISSN: 1661-7827; 1660-4601

This study investigated the cross-sectional and longitudinal associations of the substitution of non-school time light physical activity (LPA), moderate-to-vigorous physical activity (MVPA), and sedentary time (ST) with adiposity in boys and girls. Boys (<i>n</i> = 65, baseline <i>M</i>age= 9.93 ± 0.86 years) and girls (<i>n</i> = 77, baseline <i>M</i>age = 10.17 ± 0.95 years) wore waist-worn accelerometers (ActiGraph GT3X) at baseline and at a 30-month follow-up, from which non-school time LPA, MVPA, ST, and total device wear were quantified. Body mass index (BMI) and waist-to-height-ratio (WHR) were measured at baseline and follow-up. Body fat percent (BF%) was obtained at follow-up only. Isotemporal substitution models assessed the cross-sectional and longitudinal associations of reallocating non-school time activity with BMI, WHR and BF%. In boys, replacing 30 min/day of LPA with MVPA was cross-sectionally (β = −8.26, <i>p</i> < 0.05) associated with a lower BF%. Replacing 30 min/day of ST with MVPA was cross-sectionally (β = −6.02, <i>p</i> < 0.05) associated with a lower BF% in boys. Longitudinally in boys, replacing 30 min of change in LPA with MVPA (β = −7.42, <i>p</i> < 0.10) and replacing 30 min of change in MVPA with ST (β = 5.78, <i>p</i> < 0.10) over 30 months was marginally associated with less BF%. Associations were null in girls (<i>p</i> > 0.05). These results may support targeting activity reallocation during non-school time for the purposes of adiposity improvement in boys. A multi-behavioral approach may be more appropriate for girls, as non-school time activity may not be driving adiposity status.