Heather Massey of the Extreme Environments Laboratory, School of Sport, Health and Exercise Science at the University of Portsmouth, scales the heights of science on altitude training.
Among elite competitors, altitude training has become an accepted practice carefully woven into periodised training programmes, the aim being to improve subsequent performance at altitude or at sea level. The desired performance improvement can occur as a result of the change in environment that stimulates continued adaptation to a greater extent than may occur through training at sea level alone.
Advances in technology have expanded the range of options for altitude training and made it more accessible. There is no longer a need to go to altitude to train in a low oxygen environment. Services and equipment can be readily purchased to enable individuals to live or train in hypoxic (low oxygen) environments. However, there are many considerations that need to be carefully addressed before training at altitude or in hypoxic facilities.
Altitude training methods
Travelling to terrestrial altitude mountains (a hypobaric hypoxic environment) results in a reduced barometric pressure (due to the altitude) with an unchanged fraction of inspired oxygen (~21%). We can also simulate altitude exposures at sea level by reducing the fraction of available oxygen while maintaining sea level barometric pressures. These simulated altitudes can be achieved using chambers and tents in which the concentration of oxygen and nitrogen are closely controlled.
Both methods of hypoxic exposure result in low blood oxygen levels (arterial hypoxaemia). Yet, limited study has looked at the separate effect that barometric pressure has, and if this in itself results in adaptive responses over and above that of hypoxia.
There is a variety of altitude training practices available: all have advantages and disadvantages and will depend on the person’s budget, access and available time. These methods include ‘live high, train high’, ‘live high, train low’ and ‘live low, train high’ practices that can incorporate different exercise programmes or even passive exposure. More information is given in Table 1.
Table 1: Altitude training practices
| Altitude training type | Achieved by | Positives | Negatives |
| Live high, train high (LHTH)
|
Living at natural altitudes
|
Maximises opportunity for adaptive responses | Training intensity is reduced and may lead to a detraining effect when working at high intensities |
| Live high, train low (LHTL)
|
Travel between moderate altitude to live and low altitude to train
Living at natural altitude and using supplemental oxygen during training
Living in a hypoxic tent/hypoxic hotel when not training |
Is able to maintain training intensity
Remains in one venue to live and train
Is able to remain in one venue, possibly home training venue |
Much travel, expense and difficult access to locations that enable this
Practical issues of using supplemental oxygen while training, only possible in some sports
Need to accumulate 12+ hours’ exposure per day to stimulate a response |
| Live low, train high (LLTH)
|
Using a hypoxic tent to train in | Option to train at high intensities at sea level | Exposure time may be insufficient |
| Intermittent hypoxic exposure (IHE)
|
Brief resting exposures (typically repeated 1-3mins of exposure) | Limited impact on training and other activities | Exposure time is insufficient |
Why train high?
Aerobic exercise capacity reduces with ascent to altitude resulting from a reduction in barometric pressure, arterial oxygen pressure and, ultimately, oxygen saturation (which can be estimated using a pulse oximeter finger or ear probe). This reduced blood oxygen saturation stabilises hypoxic inducible factor 1 and sets off a cascade of responses that can enhance aerobic capacity by increasing the transport and extraction of oxygen to, and in, the muscle. These include increase in red blood cell count; angiogenesis; and altering the regulation between glycolytic and oxidative metabolism. These adaptations improve tolerance to lower oxygen availability and may improve performance at altitude and sea level in some individuals.
Increases in muscle function and hypertrophy have been reported from hypoxic training but are not universally agreed1. More recently, attention has turned to whole-body resistance training exercises in hypoxia, purporting to stimulate a greater metabolic stress, recruit a greater number of motor units and, therefore, increase the adaptive stimulus to a larger proportion of the muscle. However, the research is inconsistent and doesn’t reliably indicate that resistance training in hypoxia is any more beneficial than resistance training in normoxia2.
Problems/contraindications
Being at altitude does highlight a number of concerns, which may reduce or prevent adaptation, as detailed below.
Sleep
Quite frequently, when ascending to terrestrial altitudes, sleep is disturbed for the first few nights. Between 25-35% of people will experience sleep disruption caused by periodic breathing, which leads to sleep apnea (breathing repeatedly stops and starts while asleep). This can improve and possibly disappear with continued acclimatisation but can also depend upon the altitude. At moderate altitudes, many find sleep improves over the first two or three nights. At higher altitudes, sleep may be profoundly affected and may not improve with continued acclimatisation3. Using hypoxic generators at sea-level altitudes in your own home can also challenge sleep, the generators can be noisy, and sleeping wearing a mask or in a tent may disturb sleep until used to the feeling. Consideration of partners should also be given if using a hypoxic generator at home, as the units are typically designed for one person.
Dehydration and weight loss
Dehydration is a common problem at altitude. Elevated ventilation stimulated by hypoxia results in a greater respiratory water loss in addition to that lost from sweating. The greater UV levels increase the risk of sunburn: sunscreen should be worn whenever outside, regardless of the weather conditions. Altitude and hypoxic environments may also result in a loss of appetite, leading to weight loss. Consequently, fluid and food consumption should be at the forefront of athletes’ and coaches’ minds.
Altitude-related illnesses
Some people experience symptoms of acute mountain sickness (headache, nausea/vomiting, fatigue, sleep problems and dizziness); these may impact on training during the first few days at moderate altitudes. At high altitudes, acute mountain sickness (AMS) is common and exacerbated by exertion. It is rare at moderate altitudes that symptoms are sustained or worsen; they are generally self-limiting and only worsen with continued ascent. Therefore, greater altitudes don’t necessarily provide more opportunity for training adaptations to occur.
More serious and life-threatening conditions of high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE) become more prevalent at altitudes above 3,000m above sea level and with fast ascents. There are treatments which, when taken between 24-48 hours before ascent, may reduce the likelihood of altitude illness. These prophylactic treatments, Acetazolamide and Dexamethasone, are on the World Anti-Doping Agency (WADA) prohibited list4: Acetazolamide both in and out of competition; Dexamethasone, which has recently been found to have a therapeutic use for severely ill COVID-19 patients, is banned only during competition.
Athletes subject to anti-doping testing should consider the potential benefits of altitude training versus the risk of illness, treatment required to aid recovery and disrupted training. Consequently, moderate altitudes are favoured for training camps and, when using a hypoxic compressor for moderate hypoxic environments (14-15% oxygen, very roughly equivalent to altitudes of 2,500-3,000m depending on the barometric pressure), may be more convenient and provide the optimum opportunity for adaptations to occur without the risk of illness and limited training. Again, more is not always better!
Screening
Before leaving for altitude training, athletes should be monitored for signs of illness or fatigue, as well as oxygen saturation at rest and during maximal exercise; those experiencing a rapid reduction in blood oxygen saturation at high intensities may be those most susceptible to a decline in performance at altitude. Readings from pulse oximeters are influenced by blood flow to the periphery and also skin colour. Therefore, it is important to ensure that measurements are made with warm extremities and that they are used to assess previous readings of the same individual.
Hypoxic exposure increases iron requirements and utilisation for erythropoiesis (increasing red blood cell counts) in athletes. Research has shown that iron deficiency in athletes inhibits accelerated erythropoiesis when at moderate high altitude and may preclude a potential improvement in sea-level athletic performance with altitude training5. In those with an iron deficiency, iron replacement therapy before and during altitude exposure is important to maximise physiological adaptation and performance gains from altitude training.
Sleep studies/sleep quality should be monitored before altitude exposure; those with poor sleep architecture may respond poorly during altitude/hypoxic exposure3. The causes of poor sleep quality should be addressed before adding in altitude training programmes.
Who will benefit most?
Elite athletes will always look for ways to enhance performance, promote more rapid recovery and better adapt to their competitive environment in a way that can advantage them the most. It is clear that, for some athletes, altitude training has clear benefits, but these are not guaranteed for all3, and can be expensive and disruptive to training. There may also be a place for resistance training in hypoxia to impact on resistance-trained athletes, as well as play a therapeutic role in slowing the development of sarcopenia in elderly populations6, but more evidence is needed in both cases.
Monitoring is required to assess responses to training, given that the hypoxic environment may lead to an increased risk of illness and overtraining. It is not just a question of monitoring while at altitude or in hypoxic environments, but in the lead-up, during and after altitude/hypoxic training to ensure the person is healthy and, therefore, most receptive to altitude/hypoxic training.
An optimal hypoxic/altitude training programme needs flexibility. More is not always better, and the training intensity and duration of training may need to be reduced to prevent over-reaching. A monitoring programme instigated before leaving for altitude is a good means to highlight any potential problems. A great example of a monitoring programme conducted with elite distance runners is described by Sperlich et al7. Training load of the next session was adjusted if two or more of the 11 markers used were outside the athlete’s normal range. These markers include measures of training intensity and volume, iron status, pulse oximetry and perceptual measures of sleep quality and quantity, fatigue, illness and recovery, as well as body mass, body composition and resting heart rate.
Hypoxic hype: How to get the best results
Firstly, optimise training, sleep quality and iron status at sea level before considering altitude/hypoxic training.
Those previously thought to be ‘non-responders to altitude acclimatisation training’ may be a product of ‘one-off’ camps and/or inadequate planning, periodisation, programming and monitoring of altitude training. Indeed, several altitude-training studies have used single exposures in non-acclimatised altitude novices, whereas elite endurance athletes typically utilise altitude training multiple times throughout a season in preparation for competition. In keeping with this suggestion, multiple altitude training camps (>60 days/year) were a significant part of many successful athletic programmes, but whether altitude training was the main stimulus of the success is not clear. Coaches and athletes interested in the detailed programming of altitude training are referred to by Mujika et al8.
Repeated altitude training camps may be useful in the lead up to a competition. Faster re-adaptation to altitude and hypoxia occurs within three weeks of re-ascent following the first exposure9. This facilitates the taper and high-intensity pre-competition training at sea level and rapid physiological re-adaptation to altitude. In addition, a short duration exposure at moderate natural altitude (2,220m) is a very effective pre-acclimatisation strategy for subsequent higher-altitude exposure (4,300m) in comparison with a direct ascent. This approach may speed up re-acclimatisation and decrease the negative effects of altitude ascents.
One of the issues for coaches and athletes attending altitude camps is the ideal timing of return from altitude prior to competition. Some endurance athletes are known to achieve outstanding performances at various timepoints upon return to sea level after altitude training. Experts and practitioners often suggest there might be an immediate sea-level performance window (first few days) upon returning from an altitude sojourn, followed by a second window (>3 weeks’ post-altitude) when optimal performances might be best realised. However, the timing of peak performance following altitude training is likely to be influenced by a combination of altitude acclimatisation and de-acclimatisation responses, but, more importantly, also by periodisation of and responses to training and tapering conducted at altitude and immediately following. At this stage, there is more art than science to the optimal timing of post-altitude performance peaking, and an individualised approach may still be required even when research becomes available.
Take-home messages
- Altitude training has the potential to provide a natural method of enhancing performance both at sea level and for altitude competition. However, it is not a substitute for good-quality sea-level training.
- Assessment, screening and athlete education is an important part of the altitude training process.
- Training loads and recovery require careful management and planning, before, during and after altitude training.
- It’s important the athlete understands the symptoms of acute mountain sickness and how to combat the effects.
- The intensity of training must be reduced at altitude. It is easier to push into over-reaching and over training when at altitude.
- Athletes must maintain a hydrated state and precautions against sun burn are also very important.
Author Bio:
Heather Massey is a senior lecturer within the School of Sport, Health and Exercise Science. She has been a member of the Extreme Environments Laboratory since 2007 where she completed a PhD in the area of Environmental Cross-adaptation in Humans. Prior to that she worked at the Institute of Naval Medicine within the Environmental Medicine Unit for six years.
References
1. Ho JY, Kuo TY, Liu KL, Dong XY & Tung K (2014), Combining normobaric hypoxia with short-term resistance training has no additive beneficial effect on muscular performance and body composition, The Journal of Strength & Conditioning Research, 28(4): 935-941.
2. Ramos-Campo DJ, Scott B, Alcaraz PE, Rubio-Arias JA (2018), The efficacy of resistance training in hypoxia to enhance strength and muscle growth: a systematic review and meta-analysis, European Journal of Sport Science, 18(1), 92-103.
3. Pedlar C, Whyte G, Kreindler J, Hardman S & Levine B (2011), The BASES Expert statement on Human Performance in hypoxia Inducing Environments: Natural and Simulated Altitude. BASES expert statement.
4. WADA WORLD ANTI-DOPING CODE International standard prohibited list 2023, October 2022, https://www.wada-ama.org/sites/default/files/2022-09/2023list_en_final_9_september_2022.pdf, accessed 6 December 2022.
5. Okazaki K, Stray-Gundersen J, Chapman RF, Levine BD (2019), Iron insufficiency diminishes the erythropoietic response to moderate altitude exposure, Journal of Applied Physiology, 127(6): 1,569-78.
6. Jung WS, Kim SW, Kim JW, Park HY (2021), Resistance Training in Hypoxia as a New Therapeutic Modality for Sarcopenia-A Narrative Review, Life (Basel), 11(2): 106. doi: 10.3390/life11020106. PMID: 33573198; PMCID: PMC7912455
7. Sperlich B, Achtzehn S, de Marées M, von Papen H, Mester J (2016), Load management in elite German distance runners during 3-weeks of high-altitude training, Physiol Rep., 4(12): e12845. doi: 10.14814/phy2.12845. PMID: 27356568; PMCID: PMC4926021.
8. Mujika I, Sharma AP, Stellingwerff T (2019), Contemporary periodization of altitude training for elite endurance athletes: a narrative review, Sports Medicine, 49(11): 1,651-69.
9. Subudhi AW, Bourdillon N, Bucher J, Davis C, Elliott JE, Eutermoster M et al (2014), AltitudeOmics: the integrative physiology of human acclimatization to hypobaric hypoxia and its retention upon reascent, PLoS One, 9(3): e92191.
