This paper deals with the research of the impact of the training preparation period on the functional abilities of athletes up to 15 years of age, with special emphasis on soccer players, who at this age are in a sensitive phase of physical and motor development. The research was conducted on a sample of 12 young football players, who compete in a lower qualitative level, which further emphasizes the need for specific and adapted training. The subjects' functional abilities were assessed using two standardized tests: the beep test, which measures aerobic capacity, and the New Zealand rugby test, which assesses anaerobic endurance. The results showed statistically significant improvements in both tests after the five-week training preparatory period, thus confirming the initial research hypothesis. The beep test showed a significant increase in aerobic capacity, while the results of the New Zealand rugby test indicated an improvement in anaerobic endurance. These findings indicate that a properly structured and periodized training program can significantly improve the functional abilities of young athletes, which is a key factor for their long-term sports development. The results of this research are in line with earlier research that also emphasized the importance of targeted training during critical phases of growth and development in young athletes. These studies further underline the importance of individualizing training in this age group in order to achieve optimal results and avoid the potential negative effects of overtraining or unadapted training loads. This paper provides valuable guidelines for further research and optimization of training programs aimed at improving sports performance in young athletes.