Objectives: (1) To develop reference values for health-related fitness European children and adolescents aged 6-18 years that are the foundation for the web-based, open-access and multi-language fitness platform (FitBack); (2) To provide comparisons across European countries. Methods: This study builds on a previous large fitness reference study in European youth by: (1) widening the age demographic, (2) identifying the most recent and representative country-level data, and (3) including national data from existing fitness surveillance and monitoring systems. We used the ALPHA test battery as it comprises tests with the highest test-retest reliability, criterion/construct validity, and health-related predictive validity: the 20-m shuttle run (cardiorespiratory fitness); handgrip strength and standing long jump (muscular strength); and body height, body mass, body mass index, and waist circumference (anthropometry). Percentile values were obtained using the GAMLSS method. Results: A total of 7,966,693 data points from 34 countries (106 datasets) were used to develop sex- and age-specific percentile values. In addition, country-level rankings based on mean percentiles are provided for each fitness test, as well as an overall fitness ranking. Finally, an interactive fitness platform, including individual and group reporting, and European fitness maps, is provided and freely available at www.fitbackeurope.eu . Conclusions: This study discusses the major implications of fitness assessment in youth from a health, educational and sport perspective, and how the FitBack reference values and interactive web-based platform contribute to it. Fitness testing can be conducted in school and/or sport settings, and the interpreted results be integrated in the healthcare systems across Europe.

The authors have declared no competing interest.

This research was co-funded by the Erasmus+ Sport Programme of the European Union within the project FitBack No 613010-EPP-1-2019-1-SI-SPO-SCP and Slovenian Research Agency within the Research programme Bio-psycho-social context of kinesiology No P5-0142. FBO, JJGC, JRR and IL are supported by the University of Granada, Plan Propio de Investigacion, Visiting Scholar grants and Excellence actions: Units of Excellence; Unit of Excellence on Exercise, Nutrition and Health (UCEENS) and by the Junta de Andalucia, Consejeria de Conocimiento, Investigacion y Universidades and ERDF (SOMM17/6107/UGR).

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The entire Fitback procedures for pooling together existing fitness data was evaluated and approved by the Ethics Committee in Sports Science at the University of Ljubljana, Slovenia (the University coordinator the FitBack project).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

The availability of each of the datasets used in this study needs to be requested separately to the authors owning their data, which can be found in the references cited in the Online Supplementary Table 1.