Development of Physical Fitness in Young Athletes: A Longitudinal Meta-analysis

Abstract Background Understanding how physical fitness develops during adolescence is critical for interpreting and optimizing training and setting realistic performance expectations in youth sport. Yet, evidence-based, age-referenced benchmarks that track multiple fitness components across sports remain lacking, leaving practitioners without reliable normative trajectories to guide athlete development. Purpose This longitudinal meta-analysis estimated developmental trajectories for vertical jump, sprint, and endurance performance in male youth athletes across multiple sports using data from longitudinal studies. Methods Following PRISMA guidelines, we conducted a systematic search of MEDLINE, Web of Science, and Scopus for studies with repeated measurements of vertical jump, 10-meter sprint, and endurance performance in male youth athletes, from database inception to October 4, 2025. Analyses were restricted to males due to an insufficient number of eligible studies including female athletes. We applied a risk-of-bias assessment adapted from the Cochrane risk-of-bias tool and examined publication bias through funnel plot inspection and Egger’s regression test. We used Bayesian multilevel growth curve modeling to estimate age-related developmental trajectories, with analyses stratified by sport and test protocol. Results Twenty-eight studies met eligibility criteria, providing 41 independent samples across nine sports. Vertical jump and endurance performance exhibited curvilinear trajectories with peak velocity occurring at 13.2 years (68% CrI [±1 posterior SD]: 13.0; 13.5) and 13.8 years (68% CrI: 13.6; 14.2), respectively, overlapping the typical period of peak height velocity in male athletes. Sprint performance showed linear improvement throughout adolescence (ages 12–17) without distinct acceleration periods. Sport-specific analyses revealed varying absolute values but broadly similar developmental patterns within each fitness component, with rugby exhibiting the highest vertical jump values and minimal sport differences observed for sprint development. Conclusion The present age-referenced trajectories offer practical benchmarks for monitoring progression and setting realistic expectations in youth sport contexts. Our findings reveal distinct developmental patterns—curvilinear trajectories for vertical jump and endurance with peak improvements around ages 13–14 versus linear progression for sprint—with peak velocities coinciding with typical maturation timing Trial registration : CRD42020175084 (PROSPERO) 25/03/2020.