Systematic review and Meta-analysis of the effects of different training types on the physical fitness of football players

The intermittent high-intensity nature of football requires athletes to possess comprehensive physical reserves. Key indicators such as maximum oxygen uptake (VO₂max), anaerobic threshold speed (ATV), repeated sprinting ability (RSA), and directional agility (including ball control and non-ball situations) directly determine competitive performance and endurance in matches. In current football-specific training, three mainstream methods are widely applied: compact space group training (integrating technical skills with physical conditioning in confined spaces), high-intensity interval training (HIIT, alternating short bursts of high intensity with rest periods), and low-intensity interval training (repetitive drills under low-intensity loads). However, existing research remains inconclusive regarding whether these three approaches differ in enhancing specific physical metrics or their applicability scenarios. To systematically synthesize empirical evidence and clarify the advantages and compatibility of these training methods for football players' physical development, this study will conduct a systematic review and Meta-analysis. By comprehensively reviewing relevant clinical studies and using core physical fitness indicators as outcome variables, we will quantitatively and qualitatively evaluate the effectiveness of these three training modalities, providing evidence-based references for the precise formulation of specialized football training programs.