FormalPara Professor Olivier Girard
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This special altitude training issue of Journal of Science in Sport and Exercise contains a series of 9 articles (5 reviews and 4 original articles). These papers discuss how hypoxic/altitude training can be used effectively by athletes preparing to compete at terrestrial altitude or after return to sea level, mountaineers who venture in high mountainous areas, and patients for improving their health outcomes. My intention was to invite submissions from those with a novel, insightful and most importantly, integrative view of the potential physiological and performance benefits of altitude training. I am delighted with this unique collection of articles, clearly demonstrating that the physiology underlying any functional/performance improvement is still far from fully understood.

The effort to standardize practices for athletic performance at moderate altitude began in connection with the 1968 Olympic Games in Mexico City, where altitude was a particular pressing physiological problem to be solved [8]. The strong sense that gets from reading the Millet et al. [6] review is that in the early-1990s discovery of the hypoxia-inducible factor-1 regulatory pathway and of its molecular regulation has shifted the focus of hypoxia research towards molecular mechanisms and consequences of tissue hypoxia, most notably in cancer. The number of studies focusing on clinical and performance applications of systemic hypoxia is relatively lower. With this in mind, Burtscher et al. [3] reviewed the current knowledge on the physiology of acclimatization to hypoxia with recommendations for medical monitoring and pre-acclimatization strategies by hypoxia conditioning before going on high-altitude treks and expeditions.

In high performance sport, elite athletes who repeatedly engage in altitude training blocks likely experience a different adaptive response to altitude than novice athletes who are often recruited in experimental studies, in turn questioning the ‘real world’ implication of certain investigations [7]. By reviewing factors affecting the response to “Live High-Train High” altitude training, Sharma [10] emphasized how contextual variables likely influence erythropoiesis and production of red blood cells, as well as the maintenance of oxygen flux and training intensity at altitude. Using Team USA’s strongest medal producing Olympic sports – USA Swimming and USA Track and Field – Wilber [13] illustrated how selected altitude training strategies were successfully implemented in preparation of major international competitions, specifically the Olympic Games and World Championships.

We now better understand the physiological basis of altitude training, thanks to both new screening methods/tools and to the advent of technology, yet controversy surrounding best practice still exist [9]. At present, there is no ‘gold-standard’ screening procedure to facilitate the detection of individuals who are likely to cope well with the stress of altitude or who will respond positively. In this context, Turner et al. [12] described the usefulness of using a hypoxic sensitivity test prior to “Live High-Train High” altitude training in order to predict physiological and haematological responses in a group of endurance runners. Recently, companies marketing “altitude or elevation masks” for very reasonable costs have made claims that these face coverings can provide the same performance benefits of living or working out at altitude, and could even help prevent or treat altitude sickness. Given controversy surrounding this practice, Bellovary et al. [1] reported that a breathing restrictive mask did not produce additional metabolic stress compared to hypobaric hypoxia during steady-state exercise in moderate-altitude living individuals.

In last decade, a growing number of “Live Low-Train High” altitude training methods have emerged that include the application of systemic and local hypoxia stimuli, or a combination of both, for performance enhancement [5]. One such method is high-intensity interval training in hypoxia, which was investigated by Smith et al. [11] in female 3 × 3 basketball players. Authors observed that the addition of hypoxia to four weeks of high-intensity training improved maximal aerobic performance, shuttle run performance and muscular power compared to a normoxic condition. Another increasingly popular “Live Low-Train High” intervention is resistance training in hypoxia. By reviewing sixteen original investigations, Deldicque [4] concluded that 2–3 sessions a week performed in hypoxic conditions for 4–6 weeks with simulated altitudes between 2200 and 3500 m should be recommended to individuals looking at potentiating the effects of resistance training. Ischemic preconditioning is a local hypoxia method, which corresponds to a sequence of transient ischemic episodes followed by reperfusion. In an attempt to derive implications to accelerate or facilitate altitude acclimatization, Billaut et al. [2] summarized current knowledge on the potency of this practice to enhance the pulmonary, vascular, and metabolic determinants of performance at altitude.

As highlighted in this themed issue of the Journal of Science in Sport and Exercise, there are a large number of unresolved performance-led and mechanistic issues that still prevent practitioners from making evidence-based decisions. Translating altitude training knowledge that stems from academic research findings and applying it to the real world remains an extraordinary challenge. It is my hope that this collection of articles may help disseminate research into practice.