Revisiting the cross‐sectional and prospective association of physical activity with body composition and physical fitness in preschoolers: A compositional data approach

Summary Background Information is limited for the benefits of physical activity (PA) in preschoolers. Previous research using accelerometer‐assessed PA may be affected for multicollinearity issues. Objectives This study investigated the cross‐sectional and prospective associations of sedentary behaviour (SB) and PA with body composition and physical fitness using compositional data analysis. Methods Baseline PA and SB were collected in 4‐year‐old ( n = 315) using wrist‐worn GT3X+ during seven 24 h‐periods. Body composition (air‐displacement plethysmography) and physical fitness (PREFIT test battery) were assessed at baseline and at the 12‐month follow‐up. Results Increasing vigorous PA at expenses of lower‐intensity behaviours for 4‐year‐old was associated with body composition and physical fitness at cross‐sectional and longitudinal levels. For example, reallocating 15 min/day from lower intensities to vigorous PA at baseline was associated with higher fat‐free mass index (+0.45 kg/m 2 , 95% confidence intervals [CI]: 0.18–0.72 kg/m 2 ), higher upper‐body strength (+0.6 kg, 95% CI: 0.1–1.19 kg), higher lower‐body strength (+8 cm, 95% CI: 3–13 cm), and shorter time in completing the motor fitness test (−0.4 s, 95% CI: −0.82 to [−0.01] s) at the 12‐month follow‐up. Pairwise reallocations of time indicated that the behaviour replaced was not relevant, as long as vigorous PA was increased. Conclusions More time in vigorous PA may imply short‐ and long‐term benefits on body composition and physical fitness in preschoolers. These findings using compositional data analysis corroborate our previously published results using isotemporal substitution models.