Objectives This systematic review and meta-analysis evaluated the effects of high-intensity interval training (HIIT) on physiological adaptations and performance in competitive swimmers. Methods Following PRISMA guidelines, five databases were searched from inception to July 2025. Eligible studies included randomized controlled trials and intervention studies examining HIIT in competitive swimmers. Methodological quality was assessed using PEDro scale. Random-effects meta-analyses calculated standardized mean differences (SMDs) with 95% confidence intervals. Results Eleven intervention studies comprising 237 competitive swimmers (mean age 15.4±2.5 years) were included. HIIT significantly improved VO2max (SMD=0.86, 95% CI: 0.52-1.20, p<0.001, I2=0%) and swimming performance (SMD=0.52, 95% CI: 0.36-0.68, p<0.001). Sprint events showed greatest improvements (1.8%). Polarized training produced superior VO2max gains (8.8%) compared to traditional sprint interval training (6.6%) and threshold training (4.7%). Interventions =8 weeks yielded larger effects (SMD=0.78) than shorter protocols (<8 weeks) (SMD=0.42). Ultra-short race-pace training maintained 98.5% of target velocity with 24% lower lactate and 14% lower perceived exertion compared to traditional methods. Conclusions HIIT produces consistent improvements in aerobic capacity and swimming performance in competitive swimmers. For sprint events (50-100m), ultra-short race-pace training is recommended; for middle-distance (200-400m), polarized training; for distance events (=800m), preliminary evidence suggests that pyramidal approaches may be beneficial, though further research is needed. Minimum 8-week interventions are required for meaningful adaptations.
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