Background: The purpose of the present study was to investigate the impact of a combined Repeated Sprint Training (RST) with Large-Sided Soccer Games (LSSG) on soccer players` physical performance indicators. Methods: A randomised controlled trial protocol was designed and implemented to examine the effects of an 8-week training programme on the physical performance of U20 national team soccer players. Participants were randomly assigned after matching them based on their pre-test results from a 30 m sprint to one of two groups: an experimental group (EG; n = 16) and a control group (CG; n = 10). The EG took part in two extra training sessions per week, which included RST and LSSG, whereas the CG stuck to their usual training routine. Sprint, Repeated sprint ability (RSA), vertical jump, the New Multi-Change of Direction Agility Test (NMAT), and the 15 m ball dribbling agility test performances were assessed. Results: The main findings from this study indicate that the EG showed statistically significant improvements in short sprint performance (5 m), vertical jump height (SJ and CMJ), agility (NMAT), RSA, and fatigue tolerance, with moderate to large effect sizes. The CG showed no statistically significant changes, though some small to moderate effect sizes were observed. Conclusions: The findings suggest that this hybrid method has the potential to produce improvements in specific performance domains, particularly agility and fatigue tolerance, beyond what may be expected from regular soccer training alone.
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