Implementing a Two-Season Traditional Strength Training Intervention: Chronic Adaptations in Physical Fitness and...

This study aimed to analyze the impact of a long-term traditional strength training intervention across two full competitive seasons to evaluate physical fitness performance and external match demands in high‑performance female youth soccer players. Twenty-eight Danish female young high‑performance soccer players (age: 16.5 ± 0.8 years), belonging to two different soccer teams competing at the highest level for their age, participated in the study. Teams were allocated to either an experimental group, performing twice-weekly strength training for 2 years (EG, n = 14) or a control group (CG, n = 14). Physical fitness level, including vertical jump performance and Yo-Yo IR2 performance for maximal oxygen uptake (VO_2max), was assessed at four different time points: at the beginning of season 1; at the end of season 1; at the beginning of season 2; and the end of season 2. Additionally, players' match external demands (i.e. total distance, distance covered at speeds above 23 km·h^-1, and maximum velocity achieved) were monitored using Global Positioning System devices during four matches before and after the intervention, in the same 4 time-points. Experimental group players obtained greater improvements in both physical fitness and external match load performance, compared to the players in the control group, showing enhancements in all comparisons along the time-points (p < .05 to p < .001). These findings support the inclusion of strength training as an essential part of female soccer players' periodization, not only to improve their performance, but also to facilitate their transition to professional soccer.