Purpose: To evaluate the reliability and seasonal sensitivity of a fitness-testing battery in elite youth soccer players using 2 data-treatment methods: (1) the best score of multiple trials and (2) the mean of multiple trials. Methods: Countermovement jump (CMJ), single-leg CMJ, isometric midthigh pull, Nordic hamstring strength, 10-m sprint, 505 change of direction, and the Bronco endurance test were assessed in 24 elite academy soccer players (age 17.6 [1.0] y, height 183.5 [8.5] cm, body mass 78.2 [8.5] kg) at preseason, midseason, and end of season. Results: The CMJ, Nordic hamstring strength, 10-m sprint, 505 change of direction, and Bronco tests demonstrated high sensitivity to change (signal-to-noise ratio [SNR]: 1.14-3.08), with over 60% of athletes displaying an individual SNR >1.0. In contrast, single-leg CMJ and isometric midthigh pull relative peak force exhibited the lowest reliability and sensitivity (SNR: 0.93-1.19), with less than 60% of athletes demonstrating an individual SNR >1.0, suggesting limited utility for evaluating performance changes. While the mean of multiple trials generally yielded marginally better reliability and sensitivity, both data-treatment methods were similar. Conclusions: The majority of the studied fitness tests were reliable and sensitive enough to detect meaningful changes over a season in elite youth soccer players. Practitioners can select either the best trial or mean of trials for data analysis, depending on their context. Overall, these findings illustrate the reliability and seasonal sensitivity of common fitness tests, enabling practitioners to prioritize tests that accurately monitor player performance changes.
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