Longitudinal Tracking of Objective Measures of Cardiorespiratory Fitness, Body Composition, and Physical Activity in Children

Purpose: Understanding the longitudinal tracking of cardiorespiratory fitness (CRF), adiposity, and moderate-to-vigorous physical activity (MVPA) during childhood is essential for developing effective health interventions. Our study evaluated the tracking of objectively measured MVPA, CRF, and adiposity from early to late elementary school age. Methods: Participants were recruited through six elementary schools in the Kanto region in Japan. Of the 247 children assessed at baseline in first grade (ages 6–7), 244 participated in a follow-up in fifth grade (ages 10–11). CRF was assessed as peak oxygen uptake (VO 2 peak, mL·kg⁻¹·min⁻¹) during a progressive treadmill test. Body fat percentage was measured using dual-energy X-ray absorptiometry. MVPA was measured using a triaxial accelerometer worn for 14 consecutive days. Results: Spearman rank correlations indicated high tracking of body fat percentage in boys (ρ = 0.65, p <0.001) and girls (ρ = 0.61, p <0.001), and moderate and high tracking of MVPA in boys (ρ = 0.58, p <0.001) and girls (ρ = 0.63, p <0.001). CRF showed moderate tracking in boys (ρ = 0.57, p <0.001), but weaker tracking in girls (ρ = 0.29, p <0.01). Generalized estimating equations analysis adjusted for height revealed significant tracking for all three indicators, with a weaker tracking pattern for CRF in girls compared to boys: body fat percentage (β = 0.89 in boys, 0.79 in girls, both p <0.001), MVPA (β = 0.70 in boys, 0.69 in girls, both p <0.001), and CRF (β = 0.76 in boys, 0.54 in girls, both p <0.001). Conclusions: These findings support the need for targeted approaches during the early school years to prevent the consolidation of unfavorable profiles in fitness, adiposity, and physical activity. In addition, population-wide approaches throughout the school-age years may be important in supporting fitness development in girls, given the greater variability observed in CRF