Longitudinal trajectories of physical fitness among university students: evidence from three-year linked annual fitness records for campus health promotion

Background University is a critical period for the transition from adolescence to early adulthood, during which lifestyle and physical activity patterns become more stable. This study examines longitudinal changes in physical fitness among university students and evaluates whether trajectories differ by discipline group, baseline grade, and sex. Methods Annual physical fitness test records from 2023 to 2025 are linked at the student level. A total of 4,406 students contribute 12,795 student-year observations. Multilevel linear mixed-effects models are used to analyze total physical fitness score, with grade-based outcomes and raw item measurements used as complementary analyses. Results Total physical fitness score declines significantly from 2023 to 2025 in all discipline groups. The year × discipline-group interaction is significant, indicating different longitudinal trajectories. The largest adjusted decline is observed in Science, followed by HSSM and Engineering. Pass rates decline in all groups, while the loss of good-or-excellent status is more pronounced in Science and HSSM. Raw measurements suggest that the decline is concentrated mainly in speed, endurance, lower-limb explosive power, and muscular strength or endurance. Conclusion University students show a marked decline in physical fitness over 3 years. These findings support the use of linked annual fitness records as a campus health surveillance tool to identify declining fitness trajectories and guide stage-specific, risk-stratified health promotion strategies.