Background: This study examined the independent relationships of device-based measured sedentary time (ST) and physical activity (PA) in relation to cardiac structural and functional geometry among adolescents.

Methods: From the Avon Longitudinal Study of Parents and Children, UK birth cohort, 530 (50% female) adolescents aged 17 years had complete ST, PA, cardiac, and covariate measures. Echocardiography cardiac measures were left ventricular mass indexed for height^2.7 (LVMI^2.7 ), relative wall thickness, LV diastolic function (LVDF), and LV filling pressure (LVFP). Overweight/obesity and elevated systolic/BP hypertension were categorized as body mass index >24.99 kg/m² and ≥130 mmHg, respectively. Data were analyzed with linear regression models adjusting for cardiometabolic factors and lifestyle factors.

Results: The prevalence of overweight/obesity in males and females was 17.9% and 24.5%, respectively. The prevalence of elevated systolic BP/hypertension was 11.6% in males and 1.1% among females. The average ST was 484 ± 78 min/day, light PA was 274 ± 62 min/day, and moderate-to-vigorous PA (MVPA) was 41 ± 24 min/day, among females. Average ST, LPA, and MVPA were 468 ± 87 min/day, 293 ± 70 min/day, and 56 ± 30 min/day, respectively, among males. Higher ST was associated with higher LVMI^2.7 (standardized β = 0.16; p = 0.01) among females, but higher ST was associated with lower LVDF in males (β = -0.14; p = 0.04). Higher ST and MVPA were associated with higher LVMI^2.7 in the total cohort, normal weight, and overweight/obese adolescents. Light PA was associated with higher LVDF in the total cohort and normotensives and lower LVFP among adolescents with high lean mass.

Conclusions: Higher ST and MVPA were associated with higher LVMI; however, ST-associated LVMI increase was threefold higher than MVPA-associated LVMI increase. Higher LPA was associated with better cardiac function. Reducing ST and increasing LPA may attenuate the risk of altered cardiac structure and function in adolescents.