High-Intensity Interval Training (HIIT) in Hypoxia Improves Maximal Aerobic Capacity More Than HIIT in Normoxia: A Systematic Review, Meta-Analysis, and Meta-Regression

Abstract

The present study aimed to determine the effect of high intensity interval training (HIIT) in hypoxia on maximal oxygen uptake (VO2max) compared with HIIT in normoxia with a Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA)-accordant meta-analysis and meta-regression. Studies which measured VO2max following a minimum of 2 weeks intervention featuring HIIT in hypoxia versus HIIT in normoxia were included. From 119 originally identified titles, nine studies were included (n = 194 participants). Meta-analysis was conducted on change in (∆) VO2max using standardised mean difference (SMD) and a random effects model. Meta-regression examined the relationship between the extent of environmental hypoxia (fractional inspired oxygen [FiO2]) and ∆VO2max and intervention duration and ∆VO2max. The overall SMD for ∆VO2max following HIIT in hypoxia was 1.14 (95% CI = 0.56–1.72; p < 0.001). Meta-regressions identified no significant relationship between FiO2 (coefficient estimate = 0.074, p = 0.852) or intervention duration (coefficient estimate = 0.071, p = 0.423) and ∆VO2max. In conclusion, HIIT in hypoxia improved VO2max compared to HIIT in normoxia. Neither extent of hypoxia, nor training duration modified this effect, however the range in FiO2 was small, which limits interpretation of this meta-regression. Moreover, training duration is not the only training variable known to influence ∆VO2max, and does not appropriately capture total training stress or load. This meta-analysis provides pooled evidence that HIIT in hypoxia may be more efficacious at improving VO2max than HIIT in normoxia. The application of these data suggest adding a hypoxic stimuli to a period of HIIT may be more effective at improving VO2max than HIIT alone. Therefore, coaches and athletes with access to altitude (either natural or simulated) should consider implementing HIIT in hypoxia, rather than HIIT in normoxia where possible, assuming no negative side effects.

Examining the Effects of Altitude on Workload Demands in Professional Basketball Players during the Preseason Phase

“…In addition, the increased aerobic demands under hypoxia concur with past studies documenting superior VO2 MAX development [11] and faster heart rate recovery [34] in basketball players after altitude training. The authors of [15] found that HIIT in hypoxia improved maximum aerobic capacity more than HIIT in normoxia.…”

“…A few studies in basketball have shown the improvement of aerobic capacities [12], high-intensity running performance [13], and on-court high-intensity actions (sprints, jumps, change in direction, etc.) following hypoxic training [14,15].…”

Effects of various living-low and training-high modes with distinct training prescriptions on sea-level performance: A network meta-analysis

“…However, some perspectives have highlighted that previous studies did not consider the potential impact of variable training prescriptions [ 10 , 14 ]. Recent meta-analyses have also suggested that high-intensity interval training [ 33 ] or repeated sprint training [ 34 ] in a hypoxic condition can effectively improve performance or aerobic capacity in athletes. Training at different duration and intensities has been shown to place diverse physiological demands on the body, leading to potential differences in subsequent adaptive changes, irrespective of whether the environment is normoxic or hypoxic [ 28 , 35 ].…”

Inter-effort recovery hypoxia: a new paradigm in sport science?

“…Although adding hypoxia during interval training may result in greater performance gains compared with the same training performed in normoxia, 6 7 reductions in the intensities compared with the same training performed in normoxia have been reported during aerobic interval training in altitude. 8 Although, in general, interval training in hypoxia improves VO 2 max more than interval training in normoxia, 9 contradictory responses to the addition of hypoxia have been demonstrated depending on the variation of the interval training, 5 which may 6 7 or not 10 11 improve performance.…”