The effects of strength and conditioning programs on soccer players’ performance across a single season divided into two phases

Purpose This study aimed to analyze variations in specific endurance, assessed by the Yo-Yo Recovery-Level 1 test, and estimated VO₂max across different phases of a competitive soccer season. Additionally, it examined the relationship between body composition and endurance performance to understand factors influencing physical performance. Methods Twenty professional soccer players participated in this study, with performance measurements taken at six key points throughout the season. The Yo-Yo Recovery-Level 1 test, VO₂max estimation, and body composition analysis were conducted. Statistical analyses included one-way repeated measures ANOVA, Pearson correlation, and effect size calculations. Results The first preparatory phase yielded significant improvements in the Yo-Yo Recovery-Level 1 test (p < 0.05, effect size = 1.6) and VO₂max (p < 0.05, effect size = 5.5), attributed to low baseline performance levels. While the first competitive phase showed modest performance gains (p < 0.05, effect size = 0.9), subsequent phases primarily involved performance maintenance, with minor declines observed during the second competitive phase. Body composition analysis revealed that increased body fat negatively impacted endurance, while higher body water content positively influenced performance. Interestingly, increased muscle mass correlated negatively with endurance, likely due to insufficient cardiovascular conditioning. Conclusions This study highlights the critical role of structured training during the preparatory phase and active recovery during rest periods in sustaining performance throughout the season. It underscores the detrimental effects of increased body fat on endurance and the potential limitations of excessive muscle mass without adequate conditioning.