Background: Multiple occasions of device-measured physical activity have not been previously
examined in relation to metabolic traits. We described associations of total activity, moderate-tovigorous physical activity (MVPA), and sedentary time from three accelerometry measures taken
across adolescence with detailed traits related to systemic metabolism.
Methods and Findings: 1826 male and female participants recruited at birth in 1991-92 via mothers into the Avon Longitudinal Study of Parents and Children offspring cohort who attended clinics in 2003-05, 2005-06, and 2006-08 were included in ≥ 1 analysis. Waist-worn uniaxial accelerometers measured total activity (counts/min), MVPA (min/day), and sedentary time (min/day) over ≥ 3 days at age 12y, 14y, and 15y. Current activity (at age 15y), mean activity across occasions, interaction by previous activity, and change in activity were examined in relation to systolic and diastolic blood pressure, insulin, C-reactive protein, and 230 traits from targeted metabolomics (nuclear magnetic resonance spectroscopy) including lipoprotein cholesterol and triglycerides, amino and fatty acids, glycoprotein acetyls, and others, at age 15y. Mean current total activity was 477.5 counts/min (SD=164.0) while mean MVPA and sedentary time durations were 23.6 min/day (SD=17.9) and 434.5 min/day (SD=64.7), respectively. Mean body mass index at age 15y was 21.4 kg/m2 (SD=3.5). Withinmeasure correlations between first and last activity measurement occasions were low (e.g. r=0.40 for counts/min). Current activity was most strongly associated with cholesterol and triglycerides in HDL and VLDL particles (e.g. -0.002 mmol/l or -0.18 SD-units; 95% CI=-0.24, -0.11 for triglycerides in chylomicrons and XL-VLDL) and with glycoprotein acetyls (-0.02 mmol/l or -0.16 SD-units; 95% CI=-0.22, -0.10), among others. Associations were similar for mean activity across 3 occasions. Attenuations were modest with adjustment for fat mass index based on dual-energy x-ray absorptiometry. In mutually adjusted models, higher MVPA and sedentary time were oppositely associated with cholesterol and triglycerides in VLDL and HDL particles; MVPA more strongly with glycoprotein acetyls and sedentary time more strongly with amino acids. Associations appeared less consistent for sedentary time than for MVPA based on longer-term measures and were weak for change in all activity types from age 12-15y. Evidence was also weak for interaction between activity types at age 15y and previous activity measures in relation to most traits (minimum P=0.003; median
P=0.26 for counts/min) with interaction coefficients mostly positive. Study limitations include modest sample sizes and relatively short durations of accelerometry measurement on each occasion (3-7 days) and of time lengths between first and last accelerometry occasions (< 4 years) which can obscure patterns from chance variation and limit description of activity trajectories. Activity was also recorded using uniaxial accelerometers which predated more sensitive triaxial devices.
Conclusions: Our results support associations of physical activity with metabolic traits that are small in magnitude and more robust for higher MVPA than lower sedentary time. Activity fluctuates over time, but associations of current activity with most metabolic traits do not differ by previous activity. This suggests that the metabolic effects of physical activity, if causal, depend on most recent engagement.