Hypoxic training as a doping method – the final whistle from Norway and Italy

Is this the final whistle to the comparison between hypoxic training and blood doping? The last two countries (Norway and Italy) that have edited laws in the 2000s for prohibiting the use of hypoxic devices in sport have lifted their bans in recent years. Here we retrace 20 years of procedure where controversies and polarized positions intersect: the recent history of the 'simulated altitude/hypoxic' methods and their use by athletes. Norwegian endurance athletes, mainly cross-country skiers and biathletes, have considerable and lengthy experience in 'simulated altitude/hypoxia' since they used a hypobaric hypoxic chamber (in Trysil) between 1995 and 2003. After this period, the Norwegian Sports Council prohibited 'simulated altitude' (both, normobaric and hypobaric hypoxia) methods until 2021, when the ban was lifted. On 26 January 2023, the Norwegian Olympic Committee published recommendations for the safe and optimal use of the aforementioned equipment by athletes. It is noteworthy that numerous pertinent points were identified as potential risks (e.g. 'poor air quality, respiratory irritation, fire hazard, poorer sleep and recovery'), yet also the potential distinctions between hypobaric (i.e. natural/terrestrial) and normobaric (i.e. simulated) hypoxia (e.g. 'simulated altitude is always a supplement, and not a substitute for terrestrial altitude') (Millet & Debevec, 2020). Similarly, in 2007, Italy banned hypoxic devices (decree of 24 January 2007, revision of the law No. 376 of 14 December 2000) arguing that 'the use of hypobaric/hypoxic chamber is prohibited because it was considered a doping practice'. This ban was imposed due to 'concerns that athletes were artificially increasing their red blood cell production and thus enhancing their performance'. It was banned also due to concerns regarding the safety of the athletes. Briefly, athletes were allowed to acclimatize to terrestrial high altitude, but not 'artificially' using hypobaric/normobaric hypoxic chambers. This point has been the subject of lively debate between Italian [e.g. Ferretti (2010) vs. Lippi & Franchini (2010)] and international (Boning, 2010; Sanchis-Gomar et al., 2010) exercise physiologists. During the same period (2003–2007), the scientific committee of the World Anti-Doping Agency (WADA), led by Dr Rabin, considered a potential ban on the use of artificial altitude environments, arguing that 'such conditions can significantly enhance performance when properly applied, by increasing the endogenous production of erythropoietin (EPO) with a subsequent elevation of red blood cell production and a better oxygen transfer to the muscles'. On 10 May 2006, a group of 76 physicians, bioethicists and sports scientists with experience in the field of hypoxia endorsed a letter written by Prof. Levine to contest the relevance of such a ban (Levine, 2006), based on the three criteria used by WADA to prohibit a substance or method (Sanchis-Gomar et al., 2010): ergogenic effect, safety and the 'spirit of sport'. In conclusion, the outcome was that WADA did not prohibit the use of hypoxic methods, but just the use of such devices within the Olympic village. A contradictory argument emerged in the 2010s. Instead of the previously held position that the altitude/hypoxic methods 'are too effective and considered as doping', the position became as 'ineffective and without scientific foundations'. Briefly, the argument put forth was that altitude/hypoxic training (either 'living high-training high', LHTH, or 'living high-training low', LHTL) was deemed irrelevant in elite endurance athletes who have – by definition – high values of maximal oxygen consumption ( V ̇ O 2 max V̇_O₂max ) and total haemoglobin mass (tHbmass) and therefore have reached a physiological ceiling (Lundby & Robach, 2016; Robach & Lundby, 2012). Further analysis refuted this assumption, demonstrating an ergogenic effect of altitude/hypoxic training even in athletes with already high Hbmass values (Millet, Chapman, et al., 2019). Such debate has the merit of highlighting the fact that the gains related to altitude/hypoxic training are not systematic, with a high intra- and inter-individual variability. It is noteworthy that, despite a disputable potential placebo effect (Siebenmann et al., 2012) or several altitude-associated risks (e.g. maladaptation) (Debevec & Millet, 2014; Dempsey & Morgan, 2015), the remain debated (Millet & Brocherie, 2020; Siebenmann & Dempsey, 2020), and the majority (75%) of the endurance athletes considered altitude/hypoxia to be 'a very important factor in their training regime' (Turner et al., 2019). In our eyes, this latter point is very important from a practical point of view. During the last decade, novel hypoxic methods have emerged, collectively referred to as 'living low-training high' (LLTH) approaches, with the premise to improve performance in intermittent (e.g. team- or racket-) sports (Faiss et al., 2013; Millet, Girard, et al., 2019). This widens the use of hypoxic devices or methods beyond the circle of endurance sports and emphasizes some non-haematological (e.g. at peripheral, vascular and/or neuromuscular level) adaptations. The advances have logically led to the combination of 'traditional' chronic altitude/hypoxic exposure (i.e. LHTH and LHTL focusing on central adaptations indicated by the increases in V ̇ O 2 max V̇_O₂max and tHbmass) and the aforementioned innovative acute methods (e.g. the 'repeated-sprint training in hypoxia, RSH, focusing on specific muscle resistance to fatigue) (Brocherie et al., 2015), in order to induce concomitant haematological and non-haematological adaptations to boost both aerobic and anaerobic energy pathways. The next steps involve a better understanding of altitude/hypoxic training with other training components (e.g. dose–response, combination with other environmental stressors) to enhance the support provided by sports scientists, coaches and staff to athletes striving for peak performance. France is an interesting example since, in preparation for the 2024 Paris Olympic and Paralympic Games, the Ministry of Sport allocated 1.5 million Euros to better integrate altitude/hypoxic training in their training programme, to better understand the mechanisms and the combination with the other training components. Interestingly, the expertise gained in altitude/hypoxic training may also have some transferability and benefit in clinical settings (Burtscher et al., 2024). Over time, scientific evidence has increasingly indicated that the Norwegian and Italian bans were not necessary, even when the 'precautionary principle' prevails in such cases. Ultimately, the voice of athletes was listened to, and the pros and cons of artificial altitude training were discussed and assessed within the scientific community, resulting in the bans being lifted for their benefit. We may consider this to be the final whistle of a lengthy and complex process. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. None declared. G.M.: Conception or design of the work, drafting the work or revising it critically for important intellectual content, final approval of the version to be published and agreement to be accountable for all aspects of the work. F.B.: Conception or design of the work, drafting the work or revising it critically for important intellectual content, final approval of the version to be published and agreement to be accountable for all aspects of the work. All authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. None. We thank Guia Tagliapietra for the translation of the Italian official documents.