**5. Conclusions**

The experimental rules, namely the reduction in the number of players, field size, and goal size, promoted the realization of more actions and more variability in these actions. There was a significant increase in the passes that passed through defensive lines and a greater number of actions in the offensive zone. The experimental format better fits the players' individual progression (U-12) and players' and teams' collective development, and it will allow the players to evolve from the individual development of previous stages. The rules of youth sport play a critical role in a player's LTAD. Future studies are necessary to establish the proper rules for each age group to facilitate their appropriate development.

**Author Contributions:** Conceptualization, A.G.-A., E.O.-T., J.M.G.-E., F.J.G.-A. and J.M.P.; Data curation, E.O.-T., J.M.G.-E. and F.J.G.-A.; Formal analysis, E.O.-T. and J.M.P.; Investigation, A.G.-A., E.O.-T., J.M.G.-E., F.J.G.-A., and J.M.P.; Methodology, A.G.-A., E.O.-T., J.M.G.-E., F.J.G.-A. and J.M.P.; Software, E.O.-T. and J.M.P.; Supervision, A.G.-A., E.O.-T. and J.M.P.; Visualization, A.G.-A., E.O.-T., J.M.G.-E., F.J.G.-A. and J.M.P.; Writing—original draft preparation, A.G.-A., E.O.-T. and J.M.P.; Writing—review and editing, A.G.-A., E.O.-T. and J.M.P.; Funding acquisition: E.O.-T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Science and Innovation, Spain, under Grant DEP2010-16140. Project "Salvador de Madariaga", of the Ministry of Education, culture and sport (PRX16 / 00422). Murcia Regional Football Association's (Spain), Football Proyect, under Grant FFRM-UMU-04 0092 321B 64502 14704. And Ministry of Economy, Industry and Competitiveness, under Grant DEP2017-90641-REDT.

**Conflicts of Interest:** The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

International Journal of *Environmental Research and Public Health*
