Arterial stiffness, cIMT, and carotid elasticity are crucial indicators of cardiovascular health, linked to morbidity and mortality. While studies have explored the relationship between objectively measured sedentary time (ST) and physical activity (PA) with metabolic markers in young people, evidence on arterial structure and function is limited. This gap may be due to a lack of gold-standard measures of arterial health and objective assessments of ST, LPA, and MVPA in large pediatric populations. Recent research suggests that ST may contribute more to left ventricular mass than MVPA, and arterial stiffness may influence the BP-left ventricular mass relationship. Body composition, BP, and metabolic markers are known determinants of arterial health in youth, yet their role in mediating the associations between movement behavior and arterial health remains unclear. This study aimed to investigate the mediating effect of total body fat mass, lean mass, BP, and insulin resistance on the associations of ST, LPA, and MVPA with cfPWV, cIMT, and carotid elasticity in adolescents from the Avon Longitudinal Study of Parents and Children (ALSPAC).

Existing literature demonstrates a link between physical activity and improved metabolic health; however, its impact on vascular health is still debated. Studies show associations between sedentary behavior and increased risk of obesity, dyslipidemia, inflammation, and cardiac hypertrophy, but its role in vascular health requires further investigation. Some research indicates a link between objectively measured sedentary time and worse metabolic and cardiac profiles, and higher arterial stiffness in children and adolescents. Conversely, other studies found no such association between sedentary behavior and arterial stiffness or other vascular measures. The mediating role of factors like BMI, waist circumference, and blood pressure has been examined, with varying findings reported.

Data from 1574 ALSPAC participants (56.2% female; mean age 15.4 years) with complete data on ST, LPA, and MVPA at age 15 and arterial measurements at age 17 were analyzed. ST, LPA, and MVPA were assessed using ActiGraph accelerometers. Body composition (fat mass, lean mass) was assessed using dual-energy X-ray absorptiometry (DEXA). cfPWV, cIMT, and carotid elasticity were measured using Vicorder and ultrasound. Cardiometabolic and lifestyle factors (BP, insulin resistance, lipids, smoking, family history) were also collected. Mediation analyses using structural equation models and linear mixed-effect models, adjusted for relevant covariates, were conducted to assess the mediating effects of fat mass, lean mass, BP, and insulin resistance on the associations of ST, LPA, and MVPA with cfPWV, cIMT, and carotid elasticity. Multiple imputation was used to handle missing data. Analyses were also stratified by sex and systolic hypertension status.

Females had higher ST, lower LPA and MVPA, lower cfPWV and carotid elasticity, higher fat mass and insulin resistance, and lower lean mass and systolic BP than males. Higher ST was associated with lower cIMT, with lean mass partially mediating this association (11.8%). Higher LPA and the highest LPA tertile were associated with lower cfPWV. Higher MVPA was associated with higher carotid elasticity and higher cIMT (mediated by lean mass; 25.5% mediation). Insulin resistance partially mediated the association between MVPA and carotid elasticity (7.7%). The associations between movement behaviors and arterial measures were generally not significantly influenced by total body fat mass, trunk fat mass, or systolic/diastolic BP. There were no significant associations between movement behaviours and vascular indices in participants with either normal systolic BP or systolic hypertension.

This study provides valuable insights into the complex relationships between movement behaviors, body composition, cardiometabolic factors, and arterial health in adolescents. While previous studies have shown conflicting results, the use of objective measures of physical activity and gold-standard measures of body composition in a large cohort adds to our understanding. The findings suggest that LPA may exert beneficial effects on arterial function (cfPWV) by potentially lowering blood pressure, while MVPA's relationship with arterial structure is more intricate, influenced by lean mass. The paradoxical finding of increased carotid thickness with MVPA, potentially linked to vascular remodeling, requires further investigation. Sex differences highlight the importance of considering gender-specific recommendations for physical activity interventions.

This large adolescent cohort study revealed that higher LPA was associated with lower arterial stiffness, while higher MVPA was paradoxically linked to thicker carotid walls, partly due to increased lean mass. Lean mass and insulin resistance emerged as key mediators in these relationships. Future research could explore the long-term effects of different types of physical activity on arterial health, paying particular attention to gender-specific differences and the mechanisms underlying the observed associations. Interventions focusing on increasing LPA, MVPA, and muscle mass, particularly in females, may be essential in preventing subclinical atherosclerosis during adolescence.

Limitations include potential underestimation of movement behaviors due to accelerometer limitations, the time gap between activity and arterial measurements, the primarily Caucasian cohort limiting generalizability, and the observational nature of the study limiting causal inference. The use of a 7-day accelerometer assessment may not fully capture individual variations in daily physical activity patterns.