Mei Jiang, Zhou He
These findings challenge uniform weight-centric assumptions about physical fitness. They highlight the need for trajectory-informed, intersectional intervention strategies in collegiate physical education and health promotion.
BACKGROUND: Physical fitness is widely regarded as an important indicator of overall health and functional capacity. However, cross-sectional studies consistently report declining fitness levels and rising overweight/obesity among college students. Longitudinal research tracking individual developmental trajectories remains scarce, and the "fat but fit paradox" is underexplored in this population. This study aimed to model 4-year trajectories of physical fitness indicators (PFI) across body mass index (BMI) categories, and to test the existence of the "fat but fit paradox".
METHODS: This study used de-identified, individual-level longitudinal data comprising four annual physical fitness assessments from 183,075 Han Chinese college students across 140 universities in Chengdu, China. MG-LGCMs were constructed to examine developmental trajectories of physical fitness indicators, with baseline BMI category as the grouping variable and gender as a covariate.
RESULTS: Results revealed significant heterogeneity across BMI categories. The normal-weight group exhibited the highest baseline fitness yet showed non-significant linear growth, whereas the obese group, despite the lowest baseline, demonstrated the fastest improvement. For gravity-dependent indicators-endurance running, pull-ups (males), and 1-minute sit-ups (females)-overweight and obese groups initially displayed a disadvantage but subsequently improved significantly faster. Absolute forced vital capacity followed a "fat but fit paradox," with higher-BMI groups maintaining superior score across 4 years. Flexibility consistently favored the normal-weight group. Gender significantly moderated both initial status and rate of change: males showed steeper acceleration across most motor domains, while females maintained baseline superiority in flexibility.
CONCLUSION: These findings challenge uniform weight-centric assumptions about physical fitness. They highlight the need for trajectory-informed, intersectional intervention strategies in collegiate physical education and health promotion.