Objectives: To evaluate the effects of hypoxic interventions (HI) on swimming performance and physiological outcomes in competitive swimmers. Design: Systematic review and meta-analysis following PRISMA guidelines and registered in PROSPERO (CRD420251170303). Methods: Seven databases were searched to identify controlled trials comparing hypoxic and normoxic training under identical conditions. Eleven studies (n = 182 swimmers) were included. Standardized mean differences (SMD) and 95% confidence intervals (CI) were calculated using a random-effects model. Subgroup analyses were performed by event distance and simulated altitude. Results: HI produced a small but significant improvement in swimming performance (SMD = -0.34, 95% CI [-0.62, -0.06], p = 0.02) with low heterogeneity (I2 = 30%). No significant changes were observed for VO2max, HRmax, or VEmax (all p > 0.05). Subgroup analyses indicated greater benefits for 100 m and 200 m freestyle and for interventions conducted at simulated altitudes =3500 m. Conclusion: Hypoxic interventions yield meaningful yet modest enhancements in competitive swimming performance, likely through non-hematological adaptations such as improved muscle oxygen utilization and fatigue tolerance. Tailoring HI protocols to event-specific demands and sufficient hypoxic stimulus levels may optimize outcomes. Systematic Review Registration: Registered on PROSPERO (registration number: CRD420251170303).
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