Neighbourhood Environment and Cardiorespiratory Fitness in Youth: A Cross-Sectional Random Forest Analysis.

Cardiorespiratory fitness (CRF) in youth is associated with cardiometabolic outcomes and risk of early-onset cardiovascular disease. While the role of the neighbourhood environment in supporting physical activity is recognized, its contribution to CRF requires further investigation. We examined the extent to which a range of neighbourhood features predict youth CRF. Data were from the baseline visit of the Quebec Adipose and Lifestyle Investigation in Youth (QUALITY) cohort study (n=504, ages 8-10 years, Greater Montreal Area, Canada). CRF was measured as peak oxygen consumption during an incremental cycling test on an electromagnetic bike, expressed relative to body weight as the primary outcome (VO2peak/kg; mL·kg-1·min-1) and relative to fat-free mass as a sensitivity analysis (VO2peak/FFM; mL·kg FFM-1·min-1). Neighbourhood features were assessed through on-site audits and a Geographic Information System. Random forest modeling was applied to explore the predictive contribution of neighbourhood features alongside individual-level characteristics including sex, BMI z-score, Tanner stage, and moderate-to-vigorous physical activity (MVPA). This model explained 61.2% of the variance in VO2peak/kg and 40.7% in VO2peak/FFM based on out-of-bag predictions. The model identified BMI z-score, sex, and MVPA as the top three predictors, followed by several neighbourhood features. In a descriptive block-wise model comparison, out-of-bag variance explained for VO2peak/kg was 5.7 percentage points higher when neighbourhood variables were added to individual characteristics and MVPA. Overall, neighbourhood features suggested a modest contribution to predicting youth CRF. These findings are exploratory and warrant further investigation in longitudinal and intervention studies.