It is a well-accepted idea amongst elite athletes and coaches that spending time at altitude can elicit beneficial training adaptions that enhance endurance performance. However, as soon as I started my research for this article, it became clear that the scientific justification of altitude training is more limited than one would assume. This article is going to investigate what physiological mechanisms are altered as a result of long-term exposure to altitude (i.e. acclimatisation), and then discuss the research behind some of the most common altitude training protocols, and why it is so difficult to definitively conclude their effectiveness.
From immediate exposure to hypoxia (low levels of inspired oxygen), the body has to make specific alterations in order to maintain sufficient oxygen delivery to working tissues (this was discussed in depth in the previous article, in case you missed it). Adaptive responses to altitude continue working behind the scenes for as long as weeks or months with the main goal of becoming more tolerant to a low-oxygen environment. To acclimatise to altitude means improving oxygen delivery and utilisation over time, a process which is positively correlated with improvements in endurance performance.1
Blood adaptations
One of the most well-known systems to be altered while being at altitude is the blood. Red blood cells (RBC) are responsible for carrying haemoglobin, a molecule that binds to and delivers oxygen to the tissues that need it around the body. Within about 15 hours of moderate altitude exposure (over 2000m), low oxygen levels in the blood cause the kidneys to release a hormone called erythropoietin, more commonly known as EPO.2 The function of EPO is to stimulate the production of RBC.
Elevations in RBC mass by about 7% can be seen after 3 weeks of moderate altitude exposure. With a greater number of circulating RBC, more haemoglobin (1% increase per week at altitude) is available to deliver oxygen around the body, therefore leading to an increased VO2 max.1,3 More specifically, it is understood that VO2 max increases by 200ml/min per 1g/dl increase in haemoglobin.4
The activity of EPO is strengthened at higher altitudes. At 1900m, EPO activity increases by 30% compared to sea level, whereas at 4500m the increase is as large as 300%. RBC mass can increase for up to year, although it is understood to never achieve the value of those who are native to high altitude environments. It is estimated that optimal haematological adaptation are achieved after 80 days, but this process can be accelerated by travelling to higher altitudes.1
It is important to note that after about 48 hours of moderate altitude exposure, iron uptake is significantly increased by the bone marrow in order to form new molecules of haemoglobin. Without further iron supplementation, it is likely that iron deficiency could prevent optimal haematological adaptation.2
Another substance that can enhance oxygen delivery at altitude is 2,3-diphosphoglycerate (2,3-DPG). In response to hypoxia, lower levels of oxyhaemoglobin synthesis (the binding of oxygen to haemoglobin) facilitate the accumulation of 2,3-DPG.5 As a result, oxygen is more easily released at peripheral tissues, therefore increasing the amount of oxygen available to working muscles.5 With adaptation to altitude, this means that the critical oxygen pressure is decreased, meaning that lower oxygen levels have to be reached in order for oxygen uptake to be significantly lowered.1
Peripheral adaptions
Not only do adaptations occur in the blood as response to hypoxia, they may occur at any of the steps between the lungs and the muscle. When exposed to hypoxic conditions, the lack of oxygen acts as a stimulus to increase its peripheral uptake. There are several factors that may lead to this, the first being an increased muscle buffering capacity. This means that when acidic by-products accumulate from high intensity exercise, they are more effectively neutralised, therefore aiding performance.2
Myoglobin content in the muscle is also elevated. This is a molecule that stores oxygen in the muscle, so having more of it is beneficial to optimise oxygen uptake into the tissues.6
There is also greater capillarisation around the muscle fibres. With a greater network of blood capillaries surrounding the muscle tissue, it allows for more efficient oxygen uptake from the blood because the molecules don’t have to diffuse as far. It is thought that hypoxic conditions lead to the production of vascular endothelial growth factor, or VEGF, which is responsible for the production of new blood vessels.6
It is important to note that this is by no means an extensive list of possible peripheral adaptations; there are plenty more!
Training at altitude
If you ask any athlete or coach about altitude training, it is likely that they will be positive about its effects on endurance performance. For decades, athletes have used altitude training as a way to enhance aerobic physiology to prepare for competition, although when looking into the science behind it, it becomes apparent that it is not as simple as it is often assumed.4 Many scientific protocols have had major methodological issues, such as a lack of blinding, because it is impossible to prevent the participant from knowing if they are at altitude or not.7 This makes it very difficult to determine exactly how much altitude training can benefit an athlete.2
The classical method of altitude training is commonly known as ‘live high, train high’ (LHTH), with the aim of inducing adaptive responses from living at altitude, while also imposing an additional training stimulus from hypoxia.7 It is thought that the athlete should be training and living above 2000m for at least 3-4 weeks to enable any positive effect to take place. However as mentioned previously, it is impossible to carry out a gold standard scientific study in this scenario because the placebo effect cannot be ruled out when blinding participants is not possible.7
A drawback to this method of altitude training is that when exercising at a high elevation, the relative intensity of a given workload is increased, making it more difficult to elicit a large training stimulus (as discussed in the last article). This could result in a detraining effect if the athlete is unable to maintain a sufficient training load.8
To counter this problem, another method of altitude training was proposed by Levine and Stray-Gunderson in 1997.8 Named ‘live high, train low’ (LHTL), this protocol involves living at high altitude (between 1800-3000m) while training at low altitude (below 1300m). Theoretically this would allow athletes to reap the benefits of acclimatisation, while avoiding the detrimental effects of a reduced training load at altitude.2
The original study involved a 4 week training plan, where runners where randomly split into 3 groups: live low (150m), train low (150m); live high (2500m), train low (1300m); and live high (2500m), train high (2500m). Physiological measurements were recorded before and after the training plan, as well as 5km running time trial performance. They found VO2 max increased by 5% in both the LHTH and LHTL groups, however only the LHTL group achieved a significantly faster 5km time trial after the training.8
Further research has supported the idea that LHTL is currently the most effective method of altitude training. A meta-analysis of 51 studies concluded that LHTL can cause improvements in maximal endurance power output by 1-4%.9 Despite this, many studies have noted large individual differences amongst their findings.10 It seems that not all individuals respond to altitude training to the same extent. It has been suggested that if athletes already have a very high RBC mass, it is unlikely to increase further with training, meaning that altitude training may not be very beneficial to all.7
It has also been suggested that the hypoxic stimulus may not be entirely responsible for the positive training effects that take place at altitude.11 When you consider the environment of an altitude training camp, it is understandable that it could improve an athlete’s performance. Being surrounded by team mates, completing high quality training and being able to de-stress from normal life is very likely to exert a positive influence. When investigating the effectiveness of altitude training, perhaps there needs to be more control regarding the living situations to try and prevent the ‘training camp effect’ from confounding results.11
To conclude, there seems to be no doubt that training at altitude can improve endurance performance. More specifically, the LHTL method appears to be the most effective method to so. Nevertheless, it cannot be ignored that it is very difficult to produce ‘gold-standard’ scientific evidence due to the nature of altitude training. This makes it difficult to definitively conclude the magnitude of its performance enhancing effects.
References
- Drust B, Waterhouse J. Exercise at altitude. Scott Med J. 2010;55(2):31-34. doi:10.1258/rsmsmj.55.2.31
- Pinilla OCV. Exercise and Training at Altitudes: Physiological Effects and Protocols. Revista Ciencias de la Salud. 2014;12(1):115–130. doi:10.12804/revsalud12.1.2014.07
- Stray-Gundersen J, Chapman RF, Levine BD. “Living high-training low” altitude training improves sea level performance in male and female elite runners. J Appl Physiol (1985). 2001;91(3):1113-1120. doi:10.1152/jappl.2001.91.3.1113
- Bailey DM, Davies B. Physiological implications of altitude training for endurance performance at sea level: a review. Br J Sports Med. 1997;31(3):183-190. doi:10.1136/bjsm.31.3.183
- Purcell Y, Brozović B. Red cell 2,3-diphosphoglycerate concentration in man decreases with age. Nature. 1974;251(5475):511-512. doi:10.1038/251511a0
- Paralikar SJ, Paralikar JH. High-altitude medicine. Indian J Occup Environ Med. 2010;14(1):6-12. doi:10.4103/0019-5278.64608
- Lundby C, Millet GP, Calbet JA, Bärtsch P, Subudhi AW. Does ‘altitude training’ increase exercise performance in elite athletes?. Br J Sports Med. 2012;46(11):792-795. doi:10.1136/bjsports-2012-091231
- Levine BD, Stray-Gundersen J. “Living high-training low”: effect of moderate-altitude acclimatization with low-altitude training on performance. J Appl Physiol (1985). 1997;83(1):102-112. doi:10.1152/jappl.1997.83.1.102
- Bonetti DL, Hopkins WG. Sea-level exercise performance following adaptation to hypoxia: a meta-analysis. Sports Med. 2009;39(2):107-127. doi:10.2165/00007256-200939020-00002
- Robertson EY, Saunders PU, Pyne DB, Aughey RJ, Anson JM, Gore CJ. Reproducibility of performance changes to simulated live high/train low altitude. Med Sci Sports Exerc. 2010;42(2):394-401. doi:10.1249/MSS.0b013e3181b34b57
- Lundby C, Robach P. Does ‘altitude training’ increase exercise performance in elite athletes?. Exp Physiol. 2016;101(7):783-788. doi:10.1113/EP085579
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