The present study aimed to investigate the development of physical performance attributes across one competition year in male youth soccer players from different playing levels, while controlling for baseline performance, chronological age, and biological maturity. A total of 175 male Scottish youth soccer players from three distinct playing levels, such as grassroots, professional youth, and performance school, were recruited. Physical testing (linear sprint, change of direction, squat jump, and Yo-Yo Intermittent Recovery Test Level 1) was conducted for all players to establish baseline fitness and then repeated under matched conditions at the end of the same competition year. A Bayesian approach was used to estimate the size of any change in each physical test over the season, estimate the uncertainty around these changes, and estimate the probability of direction of these changes. In all cases, the players improved fitness testing metrics. The grassroot group made the greatest changes in physical performances but did not match absolute performance of the professional youth and performance school groups. Our results provide meaningful benchmark data for evaluating and interpreting isolated physical fitness metrics between distinct youth playing levels and may augment the ongoing critique of the discriminative ability of isolated physical fitness tests in youth soccer.
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