Age-related differences in physical fitness components of youth soccer players

Background and Study Aim. Soccer performance relies heavily on physical fitness components, including linear speed, explosive power, change-of-direction ability, and aerobic endurance. During early adolescence, these attributes develop alongside biological maturation and systematic training exposure, which may differentially influence performance outcomes across age groups. Despite the widespread use of standardized field-based tests to assess physical fitness in youth soccer players, the manifestation of age-related differences between closely spaced categories remains a matter of practical interest. This study aimed to investigate differences in selected physical fitness components between U13 and U15 youth soccer players using standardized field-based tests. Materials and Methods. A cross-sectional comparative design was employed with 36 male youth soccer players (U13: n = 18, mean age 12.7 ± 0.4 years; U15: n = 18, mean age 14.6 ± 0.5 years) from organized training programs at Nakhchivan State University. All participants had at least two years of systematic soccer training and were free from recent injuries. Physical fitness was assessed using the 30 m sprint test (linear speed), the standing long jump (lower-body explosive power), the Illinois agility test (change-of-direction ability), and the Yo-Yo Intermittent Recovery Test Level 1 (aerobic endurance). Data were analyzed using independent-samples t-tests and Cohen’s d effect sizes (p < 0.05). The study adhered to the Declaration of Helsinki. Informed consent was obtained from parents or guardians, and participants provided assent. Results. Statistically significant differences were found between groups in all measured variables (p < 0.001). U15 players outperformed U13 players with faster 30 m sprint times (4.41 ± 0.27 s vs. 4.82 ± 0.31 s, t = 4.12, d = 1.38), greater standing long jump distances (1.95 ± 0.18 m vs. 1.72 ± 0.15 m, t = −3.89, d = 1.40), quicker Illinois agility test times (16.93 ± 0.69 s vs. 18.21 ± 0.74 s, t = 5.06, d = 1.45), and higher Yo-Yo IR1 distances (1420 ± 260 m vs. 910 ± 210 m, t = −6.01, d = 2.15). All effect sizes were large. Conclusions. The results demonstrate clear age-related differences in physical fitness between U13 and U15 youth soccer players. Older players showed superior sprint speed, explosive power, agility, and aerobic endurance. These findings reflect the combined influence of biological maturation and accumulated training experience during early adolescence. The study highlights the importance of age-specific and developmentally appropriate training programs in youth soccer. Regular assessment of physical fitness using standardized field-based tests may support evidence-based training planning, performance monitoring, and long-term athlete development in youth soccer environments.