Effects of Altitude or Hypoxic Exposure on Endurance Running Performance: A Systematic Review and Meta-analysis.

CONTEXT: Altitude training is used widely by middle- and long-distance runners, yet its effects on performance and key physiological determinants remain inconsistently reported.

OBJECTIVE

To evaluate the effects of altitude or hypoxic exposure on endurance running performance and commonly reported physiological outcomes in middle- and long-distance runners.

DATA SOURCES: Medline, Embase, SportDiscus, and Web of Science.

STUDY SELECTION: Experimental studies involving healthy adult middle- and long-distance runners were included if they examined altitude or hypoxic exposure, included a control group, and reported running time-trial performance, maximal oxygen uptake (V.O2max ), aerobic endurance, running economy (RE), or hemoglobin-related outcomes.

STUDY

DESIGN

Systematic review and meta-analysis.

LEVEL OF EVIDENCE: Level 2.

DATA EXTRACTION: Data on performance and physiological outcomes were extracted from eligible studies. Standardized mean differences (SMDs) with 95% CIs were calculated using random-effects models.

RESULTS

A total of 19 studies met the inclusion criteria. Altitude or hypoxic exposure was associated with a small but significant improvement in time-trial performance (SMD, 0.31 [95% CI, 0.02 to 0.60]; P < 0.05). Effects on V.O2max did not reach statistical significance (SMD, 0.32 [95% CI, -0.03 to 0.67]; P = 0.07). No meaningful effects were observed for aerobic endurance (SMD, 0.12 [95% CI, -0.20 to 0.44]; P = 0.47) or RE (SMD, -0.03 [95% CI, -0.20 to 0.13]; P = 0.70). Hemoglobin concentration increased significantly after altitude or hypoxic exposure (SMD, 0.77 [95% CI, 0.19 to 1.36]; P < 0.001).

CONCLUSION

Altitude or hypoxic exposure appears to confer small improvements in time-trial performance in middle- and long-distance runners, whereas physiological responses are less consistent across outcomes and protocols.