The Effects of Intermittent Hypoxic Training Strategies on Maximal Oxygen Uptake in Healthy Humans: A Meta-analysis with Meta-regression

Background Intermittent hypoxic training aims to enhance exercise performance and health, commonly assessed through maximal oxygen uptake ( V O 2 max). Currently applied methods are live-high train-low (LHTL), live-low train-high (LLTH) and passive hypoxic conditioning (PHC). However, within these methods, numerous modes of application exist, and effectiveness is debated. Objective To determine the effect of LHTL, LLTH and PHC on V O 2 max in healthy participants, and identify factors associated with the amplitude of change in V O 2 max. Methods We conducted a systematic review with random-effects meta-analysis and meta-regression. Studies were identified through PubMed, EMBASE and Web of Science. We included controlled studies, calculating between-group standardised mean differences. Athlete and non-athlete populations were analysed separately. RoB2 was used to assess study quality and publication bias was investigated with funnel plots and the Egger’s test. Results Of the 5244 identified studies, 62 were included for analysis, resulting in a sample size of 1332 participants (610 athletes, 722 non-athletes). LHTL increased V O 2 max significantly more than control in athletes (mean difference [MD] = 2.17; 95% CI = 0.77, 3.56) but not in non-athletes (MD = 3.1; 95% CI = − 0.23, 6.43). LLTH did not increase V O 2 max significantly more than control in athletes (MD = 0.89; 95% CI = − 0.27, 2.05) but it did in non-athletes (MD = 1.70; 95% CI = 0.85, 2.54). PHC did not increase V O 2 max significantly more than control in athletes (MD = − 1.07; 95% CI = − 3.51, 1.37) but it did in non-athletes (MD = 2.26; 95% CI = 1.00, 3.52). Multivariate meta-regressions identified the severity, duration, and frequency of hypoxic exposure to be significantly associated with the change in V O 2 max. Conclusions LHTL showed a significant effect on V O 2 max in athletic populations while LLTH and PHC showed a significant effect on V O 2 max in non-athletic populations only. Future studies should target investigating which characteristics (e.g. severity, duration) of the hypoxic exposure are most beneficial.