Cross-sectional and prospective impact of reallocating sedentary time to physical activity on children's body composition.

The amount of time children spend in sedentary behaviours may have adverse health effects. To examine the substitution effects of displacing a fixed duration of sedentary time with physical activity (PA) on children's body composition. We included 386 children (197 boys). Outcomes were body mass index, waist circumference, total body fat mass and trunk fat mass assessed by dual-energy X-ray absorptiometry. Sedentary time and PA were measured with accelerometers. Data were analysed by isotemporal analyses estimating the effect of reallocating 15 and 30 min d Reallocating 15 and 30 min d Substituting sedentary time with MVPA using isotemporal analysis is associated with positive effects on body composition.