The aim of the present review was to focus on normobaric hypoxic resistance training and to discuss to what extent this method can be efficient for athletes to potentiate classical adaptations to resistance training and thereby performance.
Search terms related to the topic of the present review such as normobar*, hypox*, resistance exercise, resistance training and performance were inserted in Pubmed and Scopus. In total, 16 articles made the core of this narrative review.
Based on the available literature, 2–3 sessions a week performed in hypoxic conditions for 4–6 weeks with a FiO2 of 0.14–0.15 should recommended to athletes looking at potentiating the effects of resistance training. A large range of loads has been found to be efficient at inducing physiological effects in hypoxic vs normoxic conditions, from 20% to 90% of the 1-RM. Ideally, at least the last set should be performed to failure, if not all. Also, inter-set rest periods should be around 30 s for low-load exercise (30%–40% 1-RM), around 60 s for moderate-load exercise (60%–70% 1-RM) and 2 min for high-load exercise (85%–90% 1-RM).
While there is no one size fits all and certainly no guarantee of added value over normoxic training, each athlete looking at potentiating the effects of resistance training should try to implement some sessions in hypoxic conditions. Based on the individual response, subtle improvements may be expected on muscle strength and mass, velocity and power, as well as hormonal responses to resistance training.
Live high train high (LHTH) is the original method of altitude training used by elite athletes to enhance sea-level performance. Whilst many anecdotal reports featuring world-class performances of elite athletes at sea-level following LHTH exist, well-controlled studies of elite athletes using altitude training under ecologically valid conditions with training well characterised are still lacking. The literature is equivocal when considering the ergogenic potential of LHTH, and given the majority of controlled studies do not report enhanced sea-level performance, some scepticism regarding the efficacy of LHTH persists. Despite this, LHTH remains a popular form of altitude training utilised by elite athletes, with numerous case studies of champion athletes employing LHTH solidifying the rationale for its use during preparation for competition. Discussion of factors affecting the response to LHTH are often related to compromising either the hypoxia induced acceleration of erythropoiesis and production of red blood cells, or the maintenance of oxygen flux and training intensity at altitude. Regarding the former, iron status and supplementation, as well as hypoxic dose are often mentioned. Concerning the latter, reduced oxygen availability at altitude leading to athletes training at lower absolute intensities and the relative intensity of training sessions being clamped as equivalent to sea-level, thus also reducing absolute training intensity are frequently discussed. Other factors including immune function and the timing of competition following LHTH may also contribute to an observed performance. Less considered in the literature are those factors specific to elite athletes, namely the repeated use of altitude camps throughout a season, and the influence this may have on subsequent performance. The current narrative review aimed to summarise the current literature pertaining to LHTH in elite athletes, and furthermore describe several factors affecting performance following altitude training.
Main purposes of pre-acclimatization by hypoxia conditioning (HC) are the prevention of high-altitude illnesses and maintenance of aerobic exercise performance. However, robust evidence for those effects or evidence-based guidelines for exposure strategies, including recommendations to ensure safety, are largely lacking. Therefore, we summarize the current knowledge on the physiology of acclimatization to hypoxia and HC with the aim to derive implications for pre-acclimatization strategies before going on high-altitude treks and expeditions.
Based on the literature search and personal experience, core studies and important observations have been selected in order to present a balanced view on the current knowledge of high-altitude illnesses and the acclimatization process, specifically focusing on pre-acclimatization strategies by HC.
It may be concluded that in certain cases even short periods (e.g., 7 h) of pre-acclimatization by HC are effective, but longer periods (e.g., > 60 h) are needed to elicit more robust effects. About 300 h of HC (intermittently applied) may be the optimal preparation for extreme altitude sojourns, although every additional hour spent in hypoxia may confer further benefits. The inclusion of hypobaric exposures (i.e., real altitude) in pre-acclimatization protocols could further increase their efficacy. The level of simulated altitude is progressively increased or individually adjusted ideally. HC should not be terminated earlier than 1–2 weeks before altitude sojourn. Medical monitoring of the pre-acclimatization program is strongly recommended.
Acute exposure to altitude negatively impacts exercise tolerance and reduces athletes’ race performance due to lower atmospheric and body tissues oxygen partial pressures. Chronic exposure to altitude has also been used for several decades by athletes to increase training adaptations. However, the decline in arterial oxygen saturation also impacts 'trainability' and athletes are forced to travel to lower altitude for intensified training. For the athlete preparing for altitude, the advantages of properly timed terrestrial acclimatization and/or sea-level hypoxia-based pre-acclimatization recommendations are clear. However, the associated cost, demands, and time investment make these best-practice strategies difficult or impossible to implement for many athletes. This perspective and opinion article summarizes current knowledge on the potency of ischemic preconditioning (i.e., a sequence of transient ischemic episodes followed by reperfusion) to enhance the pulmonary, vascular, and metabolic determinants of performance at altitude with the aim to derive implications to accelerate or facilitate altitude acclimatization for varied goals. We discuss potential applications for athletes and propose innovative questions for future research in this field.
Although scientific conclusions remain equivocal, there is evidence-based research, as well as anecdotal support, suggesting that altitude training can enhance performance among Olympic level athletes, particularly in endurance sport. This appears to be due primarily to hypoxia-induced increases in total hemoglobin mass and subsequent improvements in maximal oxygen uptake and other factors contributing to aerobic performance. Although less clear, it is possible that non-hematological adaptations may contribute secondarily to improvements in post-altitude performance. These physiological effects are most likely realized when the altitude exposure is of sufficient “hypoxic dose” to provide the necessary stimuli for performance-affecting changes to occur via hypoxia-inducible factor 1α (HIF-1α) and hypoxia-inducible factor 2α (HIF-2α) pathways and their downstream molecular signaling. Team USA has made a strong commitment over the past 20 years to utilizing altitude training for the enhancement of performance in elite athletes in preparation for the Olympic Games and World Championships. Team USA’s strongest medal-producing Olympic sports—USA Swimming and USA Track and Field—embraced altitude training several years ago, and they continue to be leaders within Team USA in the practical and successful application of altitude training. Whereas USA Swimming utilizes traditional “live high and train high” (LH + TH) altitude training, USA Track and Field tends more toward the use of the altitude training strategy whereby athletes live high (and potentially sleep higher, either naturally or via simulated altitude), while training high during moderate-intensity (< lactate threshold 2) training sessions, and train low during high-intensity (> lactate threshold 2) training sessions (LH + TH[<LT] + TL[>LT]). Although USA Swimming and USA Track and Field have taken different approaches to altitude training, they have been equally successful at the Olympic Games and World Championships, both teams being ranked first in the world based on medals earned in these major international competitions. In addition to USA Swimming and USA Track and Field, several other Team USA sports have had consistently competitive performance results in conjunction with regular and systematic altitude training blocks. The purpose of this paper was to describe select altitude training strategies used by Team USA athletes, and the impact of those strategies on podium performance at major international competitions, specifically the Olympic Games and World Championships.
Elite endurance runners frequently utilise live high-train high (LHTH) altitude training to improve endurance performance at sea level (SL). Individual variability in response to the hypoxic exposure have resulted in contradictory findings. In the present case study, changes in total haemoglobin mass (tHbmass) and physiological capacity, in response to 4-weeks of LHTH were documented. We tested if a hypoxic sensitivity test (HST) could predict altitude-induced adaptations to LHTH.
Fifteen elite athletes were selected to complete 4-weeks of LHTH (~ 2400 m). Athletes visited the laboratory for preliminary testing (PRE), to determine lactate threshold (LT), lactate turn point (LTP), maximal oxygen uptake VO2max and tHbmass. During LHTH, athletes completed daily physiological measures [arterial oxygen saturation (SpO2) and body mass] and subjective wellbeing questions. Testing was repeated, for those who completed the full camp, post-LHTH (POST). Additionally, athletes completed the HST prior to LHTH.
A difference (P < 0.05) was found from PRE to POST in average tHbmass (1.8% ± 3.4%), VO2max (2.7% ± 3.4%), LT (6.1% ± 4.6%) and LTP (5.4% ± 3.8%), after 4-weeks LHTH. HST revealed a decrease in oxygen saturation at rest (ΔSpr) and higher hypoxic ventilatory response at rest (HVRr) predicted individual changes tHbmass. Lower hypoxic cardiac response at rest (HCRr) and higher HVRr predicted individual changes VO2max.
Four weeks of LHTH at ~ 2400 m increased tHbmass and enhanced physiological capacity in elite endurance runners. There was no observed relationship between these changes and baseline characteristics, pre-LHTH serum ferritin levels, or reported incidents of musculoskeletal injury or illness. The HST did however, estimate changes in tHbmass and VO2max. HST prior to LHTH could allow coaches and practitioners to better inform the acclimatisation strategies and training load application of endurance runners at altitude.
To investigate the effects of 4 weeks high-intensity interval training in hypoxia on aerobic and anaerobic performance of 3-on-3 basketball players.
In a randomised controlled trial, 15 female basketballers completed eight 1-h high-intensity training sessions in either normobaric hypoxia (hypoxic group n = 8, altitude 3052 m) or normoxia (normoxic group n = 7, sea-level).
After training, the hypoxic group increased their 1-min all-out shuttle run distance by 2.5% ± 2.3% (mean ± 95% CI, d = 0.83, P = 0.04), compared to the normoxic group 0.2% ± 2.3% (d = 0.06, P = 0.8), with the difference between groups being clinically worthwhile but not statistically significant (d = 0.77, P = 0.1). Distance covered in the Yo-Yo intermittent recovery test tended to increase in the hypoxic (32.5% ± 39.3%, d = 1.0, P = 0.1) but not normoxic group (0.3% ± 24.5%, d = 0.08, P = 0.9), with a non-significant change between groups (d = 0.9, P = 0.2). Compared to normoxia, the hypoxic group significantly increased subjective markers of stress (d = 0.53, P = 0.005), fatigue (d = 0.43, P = 0.005), and muscle soreness (d = 0.46, P = 0.01), which resulted in a lower perceived training performance in the hypoxic compared to the normoxic group (d = 0.68, P = 0.001).
High-intensity interval training under hypoxic conditions likely improved 1-min all-out shuttle run ability in female basketball 3-on-3 players but also increased subjective markers of stress and fatigue which must be taken into consideration when prescribing such training.