Although altitude training had been used for many years, the last few years it has become incredibly popular with endurance athletes. Athletes and trainers seem compelled to include hypoxia (real or simulated altitude) in their training regimen expecting additional gains through physiological adaptations (See infographic). The primary aim is to induce adaptations in blood (haematological adaptations: e.g., increase in haemoglobin mass), for an improved oxygen delivery at the muscle level. Here we will look at some of currently used methods and their evidence.
Why altitude?
The main reason why athletes are going to altitude is the idea that this will results in various advantageous haematological adaptation, including an increase in haemoglobin mass. Haemoglobin is the iron-containing protein that carries oxygen in your bloodstream towards the working muscles; and the more oxygen you can utilise, the more (aerobic = using oxygen) power you will be able to produce.
Live high-train high
For most, altitude training would preferably be defined as a prolonged stay at a moderate altitude (1800-2500 m) following strategies like "live high-train high" or the "live high-train low" to stimulate an increase in haemoglobin mass while trying to preserve training quality. Despite contentious underpinning physiological mechanisms, many key lessons were learned in the past 25 years related to hypoxic dose, timing, and individual variability in the adaptive gains, among others (1).
Individual responses to altitude
An overview of all altitude training studies to date outlines very individual responses to altitude training camps. To know if it works for you, you need to follow recommendations (e.g., at least 18 days at an optimal altitude of 2100-2500 m, while training ideally at a lower altitude, and with sufficient iron stores at the start, and optimal hydration, etc.). You will also need to try first and follow an individual plan allowing you to train and recover well before, during and after the period at altitude.
Live low-train high
Besides, facilities allowing to simulate altitude (i.e., normobaric hypoxia) in chambers or tents have allowed to use hypoxia as an additional stressor to target adaptations at the peripheral (muscular) level. This defines the “Live Low-Train High” strategy that includes all forms of “Intermittent Hypoxic Training” (IHT). It was, however, evident that "IHT leads to strikingly poor benefits for sea-level performance improvement, compared to the same training protocol performed in normal air conditions” if the exercise intensity is not set correctly (2).
Repeated-sprint training in hypoxia
This was a starting point to develop the first study with based on the repetition of short (< 30 s) “all-out” sprints with incomplete recoveries in hypoxia; the so-called Repeated-Sprint training in Hypoxia (RSH). RSH was conceived with a maximal-intensity training stimulus (i.e., “all-out” sprints) allowing to maintain a high fast-twitch fibers (FT) recruitment. In the past decade, RSH has gained great popularity among athletes. Coaches and scientists report beneficial outcomes that support RSH as an effective (but not magic) training strategy (3). A large majority of the 120 scientific studies published since the first in 2013 (4) support the efficacy of RSH when implemented in ecological sport-specific situations at a simulated (or real) altitude of ~3000 m.
Heat training
If hypoxia is not possible, heat training has also gained interest lately with several studies showing a gain in haemoglobin mass after 5 weeks of training sessions in the heat (with warm clothing or in heat chambers). The rationale behind this strategy lies in the increase in plasma volume induced when training in the heat. This would in turn dilute the red blood cells in the blood (i.e. reduce the haematocrit) with the kidneys reacting to this dilution acting as a so-called “critmeter”. In other words, the body will react to the lesser concentration of the diluted red blood cells by producing more of them. Heat training response may be linked to an increase in erythropoietin production necessary for red blood cell production. Positive changes in haemoglobin mass have recently been observed in several heat training studies with further investigations warranted to explore the exact underlying mechanisms.
Overall, training in the heat also allows an acclimation to the thermal environment that is positive for performing in the heat (and even in temperate conditions). Combining altitude and heat is attractive but more research is currently needed to define the most beneficial sequence (heat before altitude or vice versa) while simultaneous heat and hypoxic training may represent a far too strong stimulus (5).
Conclusions
In conclusion, there is certainly an interplay in the adaptive mechanisms when training in hypoxia and/or in the heat. Both conditions represent a stress adding to the training stimulus with pronounced physiological adaptations. However, these adaptations are very individual, and you should try what suits you and seek expert recommendations before blindly following protocols found in scientific publications.
Reference
Girard, O., B.D. Levine, R.F. Chapman, and R. Wilber, "Living High-Training Low" for Olympic Medal Performance: What Have We Learned 25 Years After Implementation? Int J Sports Physiol Perform, 2023. 18(6): 563-572.
Faiss, R., O. Girard, and G.P. Millet, Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia. Br J Sports Med, 2013. 47 Suppl 1(Suppl 1): i45-50.
Faiss, R., A. Raberin, F. Brocherie, and G.P. Millet, Repeated-sprint training in hypoxia: A review with 10 years of perspective. J Sports Sci, 2024: 1-15.
Faiss, R., B. Leger, J.M. Vesin, et al., Significant molecular and systemic adaptations after repeated sprint training in hypoxia. PLoS One, 2013. 8(2): e56522.
Girard, O., P. Peeling, S. Racinais, and J.D. Periard, Combining Heat and Altitude Training to Enhance Temperate, Sea-Level Performance. Int J Sports Physiol Perform, 2024. 19(3): 322-327.
