Objective: To examine grade-related changes in physical fitness indicators among undergraduate students and to explore sex differences in these trajectories, providing empirical evidence for physical education programs in universities.
Methods: Longitudinal data from undergraduate physical fitness tests conducted at a university between 2013 and 2025 were analyzed. Lung capacity, standing long jump, sit-and-reach, and the 50-m sprint were included as outcome variables. Linear mixed-effects models were applied to lung capacity, standing long jump, and sit-and-reach to account for repeated measurements within individuals. For the 50-m sprint, performance was converted to running speed (m/s) and analyzed using generalized estimating equations. Grade, sex, and their interaction were included as fixed effects, with enrollment year and gap years as covariates.
Results: A total of 14,920 students with 49,156 observations were included. Lung capacity and standing long jump performance increased significantly with grade (P<0.001), and males exhibited higher levels than females for these indicators (P<0.001). Significant grade-by-sex interactions were observed for both lung capacity and standing long jump (P<0.01), indicating smaller grade-related improvements among females. Enrollment year showed significant associations with several fitness indicators. Results for 50-m running speed were consistent with these main patterns and robust across different data-cleaning strategies.
Conclusion: Physical fitness indicators among undergraduate students demonstrate clear grade-related changes and pronounced sex differences. Findings from this longitudinal analysis provide empirical support for understanding physical fitness development in undergraduate populations and may inform physical education practices in universities.