Br J Sports Med: first published as 10.1136/bjsports-2013-092741 on 26 November 2013. Downloaded from Review Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia Raphaël Faiss,1 Olivier Girard,2 Grégoire P Millet1 1Department of Physiology, ABSTRACT extended stay in altitude.6 By adding the stress of Faculty of Biology and Over the past two decades, intermittent hypoxic training hypoxia during ‘aerobic’ or ‘anaerobic’ interval Medicine, Institute of Sports Sciences, University of (IHT), that is, a method where athletes live at or near training (INT), it is believed that IHTwould potenti- Lausanne, Lausanne, sea level but train under hypoxic conditions, has gained ate greater performance improvements compared to Switzerland unprecedented popularity. By adding the stress of similar training at sea level. For long, erythrocytosis 2 ASPETAR—Qatar Orthopaedic hypoxia during ‘aerobic’ or ‘anaerobic’ interval training, was believed to be the primary factor benefiting and Sports Medicine Hospital, it is believed that IHT would potentiate greater putative sea-level performance improvement after a Research and Education fi 457 Centre, Doha, Qatar performance improvements compared to similar training suf cient (several weeks) hypoxic stimulus. at sea level. A thorough analysis of studies including IHT, However, IHT viewed this from a new perspective Correspondence to however, leads to strikingly poor benefits for sea-level with evidence that exercising even for a short period Professor Grégoire P Millet, performance improvement, compared to the same in hypoxia affects a large number of genes mediated Department of Physiology, 8 Faculty of Biology and training method performed in normoxia. Despite the by hypoxia-inducible factors (HIFs) and the exer- Medicine, Institute of Sports positive molecular adaptations observed after various IHT cise performance with muscular adaptations arising Sciences, University of modalities, the characteristics of optimal training (and not necessarily an improved oxygen carrying – Lausanne, Géopolis, Quartier stimulus in hypoxia are still unclear and their functional capacity).9 12 Nevertheless, in other IHT studies, Mouline, Lausanne 1015, translation in terms of whole-body performance any potentiating effect of hypoxia in addition to Switzerland; 313–16 [email protected] enhancement is minimal. To overcome some of the training was ambiguous. Although an inherent limitations of IHT (lower training stimulus due improvement in anaerobic performance after IHT – Received 11 June 2013 to hypoxia), recent studies have successfully investigated has been mentioned in four studies,17 20 it is note- Accepted 11 September 2013 a new training method based on the repetition of short worthy that these studies were ‘uncontrolled’, and (<30 s) ‘all-out’ sprints with incomplete recoveries in therefore the effects of training cannot be distin- hypoxia, the so-called repeated sprint training in hypoxia guished from those of hypoxia.13 As such, it seems (RSH). The aims of the present review are therefore that after decades of research, “IHT does not threefold: first, to summarise the main mechanisms for increase exercise performance at sea level in endur- interval training and repeated sprint training in ance athletes any more than simply training at sea normoxia. Second, to critically analyse the results of the level.”21 studies involving high-intensity exercises performed in Until now, only scarce literature has assessed the http://bjsm.bmj.com/ hypoxia for sea-level performance enhancement by potential benefits of altitude training in intermittent differentiating IHT and RSH. Third, to discuss the sports.16 22 23 Therefore, the relevance of altitude potential mechanisms underpinning the effectiveness of training in team-sport athletes for improving those methods, and their inherent limitations, along with players’ specific fitness (repeated sprint ability the new research avenues surrounding this topic. (RSA)) has not been scientifically sounded as yet. Team-sport players (eg, football) perform a large number of high-intensity actions, including numer- on September 25, 2021 by guest. Protected copyright. INTRODUCTION ous sprints, often with incomplete recoveries, Prolonged altitude sojourns using the ‘live high- during the course of a game. As a consequence, train high’ or the ‘live high-train low’ models12 developing their ability to repeatedly perform have been increasingly used in athletes involved in intense exercise bouts for sustained periods is endurance and, more recently, in intermittent (eg, important for crucial match actions.24 For example, team and racket sports) disciplines in an attempt to failure to recover after a sequence of intense gain a competitive edge.23However, the question actions may leave the team more vulnerable defen- as to how effectively prolonged altitude exposure sively by decreasing the chances to reach passes or can improve athletic performance and its underpin- increasing the time to take up a defensive position ning physiological mechanisms and signalling path- (tackles). Sport-specific training methods for team ways remains contentious.45 sports using the stress of hypoxia as a strong add- Over the past two decades, intermittent hypoxic itional stimulus with specifically designed training Open Access training (IHT), that is, a method where athletes live models are arguably promising methods. For Scan to access more free content at or near sea level but train under hypoxic condi- instance, repeated sprint training in hypoxia (RSH), tions, has gained large popularity. Hence, IHT pre- defined as the repetition of several short (≤30 s) sents the advantages of minimal travel and relatively ‘all-out’ exercise bouts in hypoxia interspersed with low expense and causes limited disruption to the incomplete recoveries (exercise-to-rest ratio <1:4), To cite: Faiss R, Girard O, athletes’ normal training environment and lifestyle. could be considered as such a sport-specific training Millet GP. Br J Sports Med Another advantage is that it also avoids the deleteri- strategy. Although RSH could be considered as a – 2013;47:i45 i50. ous effect (decreased muscle excitability) of an form of IHT, its efficacy is presumably based on Faiss R, et al. Br J Sports Med 2013;47:i45–i50. doi:10.1136/bjsports-2013-092741 1 of 8 Br J Sports Med: first published as 10.1136/bjsports-2013-092741 on 26 November 2013. Downloaded from Review different mechanisms than on the existing IHT methods (dis- contribution at the start of a sprint. If the increase in H+ accu- cussed below), therefore justifying the addition of the RSH mulation is also known to impair RSA, recent findings39 suggest modality in the altitude training nomenclature.25 that this fitness component is determined to a larger extent by The aims of the present review are threefold: first, to sum- the muscle energy supply (eg, short-term (<1 min) PCr resynth- marise the main mechanisms for INT and repeated sprint train- esis rate) than by the H+ removal. ing in normoxia (RSN). Second, to critically analyse the results In team sports, the clinical relevance of improving RSA is of the studies involving high-intensity exercises performed in debated,40 but it is a common belief that such adaptations hypoxia for sea-level performance enhancement by differentiat- would be beneficial for improved match-related physical per- ing IHT and RSH. Third, to discuss the potential mechanisms formance. For instance, the mean time recorded during an RSA underpinning the effectiveness of those methods, and their test predicts the distance of high-intensity running and the total inherent limitations, along with new research avenues surround- sprint distance during a professional football match.41 ing this topic. Furthermore, football players experience temporary fatigue A computer-based literature search was conducted in April during a game (eg, lower amount of sprinting, high-intensity 2013 using the PubMed electronic database using combinations running and distance covered after a sequence of repeated and of specific keywords: ‘altitude’, ‘hypoxic’, ‘training’, ‘intermit- intense actions), which may determine the outcome of crucial tent hypoxia’, ‘repeated sprints’, ‘interval training’, ‘exercise’ situations (eg, decreased technical and tactical behaviour and and ‘performance’. Recently, an international consensus group wrong cognitive choices).42 43 This suggests that improving RSA of the IOC26 underlined the further need “to study the effects would maximise team-sport physical performance and that it is of training in hypoxia and live high-train low modalities on per- important to better understand training strategies that can formance at sea level, low and moderate altitude using a enhance this fitness component. placebo-controlled double-blind design.” Well aware of the Although the brief description above of the main determi- methodological issues (ie, importance of ruling out placebo nants of INT versus RSN highlights that those training methods effects21 27) pertaining to the conclusion of some altitude train- aim at developing predominantly the aerobic pathway and RSA, ing studies, the present review is limited to studies including a respectively, the practical question of their optimal combination control (CON) group in their experimental design, allowing the in team sports is widely debated37 44 with two diverging effects of training and hypoxic stimulus to be clearly approaches45; that is, an integrative ‘mixed’