The independent prospective associations of sedentary time, moderate and vigorous physical activity with adiposity in young adolescents

Purpose: To assess the associations between 1) baseline objectively-measured activity intensity (sedentary (SED), moderate (MPA) or vigorous (VPA) activity) and 4-year change in adiposity, and between 2) 4-year change in activity intensity and adiposity at follow-up.

Methods: Analyses of longitudinal data from the SPEEDY study, including all participants with valid data at baseline and 4-year follow-up for objectively-measured activity (Actigraph accelerometer), measured anthropometry (waist circumference (WC), %body fat (%BF), and fat mass index (FMI)), and covariates (age, sex, birth weight, dietary energy density (4-day food diary), accelerometer registered time, maternal BMI, socio-economic status, and sleep). Linear regression models with robust standard errors to account for clustering by school were fitted, interactions with sex and baseline obesity status explored.

Results: 367 participants were included (48% boys, baseline age 9-10 years). Baseline SED was not associated with change in WC (B per 10-minute increase; 95%CI: -0.11;-0.27:0.04), %BF (-0.02;-0.10:0.07), or FMI (-0.03;-0.16:0.10). All models were attenuated but remained non-significant after adjustment for moderate-to-vigorous PA. Similarly, baseline MPA and VPA were not associated with change in WC (MPA: 0.41;-0.14:0.96, VPA: 0.21;-0.20:0.62), %BF (MPA: 0.04;-0.24:0.31, VPA: 0.07;-0.17:0.31), or FMI (MPA: 0.12;-0.23:0.46, VPA: 0.00;-0.24:0.25), adjustment for SED did not change conclusions. Change in SED, MPA and VPA did not predict anthropometry at follow-up. Results did not differ by sex or baseline obesity status.

Conclusions: Objectively-measured activity intensity was not prospectively associated with adiposity in this adolescent cohort. Future research should continue to explore the importance of activity intensity on changes in adiposity, to inform intervention efforts.