Cross‐sectional and longitudinal associations between non‐school time physical activity, sedentary time, and adiposity among boys and girls: An isotemporal substitution approach

Abstract

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 (n = 65, baseline Mage= 9.93 ± 0.86 years) and girls (n = 77, baseline Mage = 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 followup 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, p < 0.05) associated with a lower BF%. Replacing 30 min/day of ST with MVPA was cross‐sectionally (β = −6.02, p < 0.05) associated with a lower BF% in boys. Longitudinally in boys, replacing 30 min of change in LPA with MVPA (β = −7.42, p < 0.10) and replacing 30 min of change in MVPA with ST (β = 5.78, p < 0.10) over 30 months was marginally associated with less BF%. Associations were null in girls (p > 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.