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.O 2max ), 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.O 2max 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.