Policy dosing in school physical education and adolescent fitness: a threshold-type association in a two-wave panel study from Kunming, China

An EPDI around 60 is a practical, exam-aligned planning benchmark, with diminishing marginal returns beyond the breakpoint and equity-relevant heterogeneity by sex and grade. Segmented and spline models outperformed linear models for most outcomes, and findings were robust across weighting/sensitivity checks. Estimates reflect one school over a short time period and should be replicated across schools/districts, accounting for maturation and socioeconomic markers. Associations are interpreted as non-causal.