# The effect of hypoxic interventions on swimming performance in competitive athletes: a systematic review and meta-analysis

## TL;DR

Hypoxic training slightly improves swimming performance in competitive athletes, particularly in short-distance events, but does not significantly affect key physiological metrics.

## Contribution

This study provides a systematic review and meta-analysis showing that hypoxic interventions modestly enhance swimming performance, likely through non-hematological adaptations.

## Key findings

- Hypoxic interventions led to a small but significant improvement in swimming performance (SMD = −0.34).
- No significant changes were observed in VO2max, HRmax, or VEmax.
- Greater benefits were found for 100 m and 200 m freestyle events and at simulated altitudes ≥3500 m.

## Abstract

To evaluate the effects of hypoxic interventions (HI) on swimming performance and physiological outcomes in competitive swimmers.

Systematic review and meta-analysis following PRISMA guidelines and registered in PROSPERO (CRD420251170303).

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.

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.

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.

Registered on PROSPERO (registration number: CRD420251170303).