The adaptations of altitude training have been well documented within the literature and have been shown to have a dramatic influence on an endurance athlete’s performance. These adaptations and improved performance are associated with an improved oxygen supply to the working muscles. The stimulus to altitude training is a decrease in the pressure of oxygen (hypoxia), which means that less oxygen can be utilised by the athlete. In response to this, the body stimulates the production of more red blood cells to increase the athlete’s oxygen-carrying capacity (Bonetti & Hopkins, 2009;Chapman, 2013; Chapman et al., 1998; Saunders et al., 2009). There are two main methods behind altitude training which are, “train high, live high” and “train low, live high”. The problem with the “train high, live high” method is that it might induce too much physical strain on the athlete and cause detraining. This is why the “train low, live high” method might be a better alternative however logistically this could be very difficult and cause other external stress to the athlete, through constantly moving (Bailey, 1997; Bonetti & Hopkins, 2009; Saunders et al., 2009).
Another limitation to altitude training is the ability or access an athlete has to the mountains or high-altitude locations. Therefore, the ability to replicate altitude training without going to the mountains would be extremely advantageous and an effective ergogenic aid for endurance performance. There is the option of altitude chambers and tents that can be used to simulate the conditions of altitude training, but they also can have logistical or practical limitations. One method that claims to simulate altitude training is breath hold training (BHT) (Harbour et al., 2022; Joulia et al., 2003). This would combat any logistical and practical limitations and could allow anyone to access the benefits of altitude training. Therefore, the purpose of this article is to critically review the adaptations to BHT to see if they have a similar response to altitude training.
It would make logical sense that an athlete would benefit from altitude adaptations through BHT. This is because during both processes the partial pressure of oxygen is being reduced and the partial pressure of carbon dioxide is increased.Therefore, this would send the same stimulus to the chemoreceptors, thereby causing them to respond by increasing the red blood cell content (Bailey et al., 1998; Joulia et al., 2003). However, the main differences between the methods are that the duration the athlete is exposed to the hypoxia environment is likely to be longer when living at altitude than fromBHT. Wyatt (2014) recommended that for an athlete to become fully acclimatised to altitude they need to be exposed to a hypoxia environment of more than 12 hours and a minimum of 3 weeks. However, the important thing to consider is that that the athlete does not necessarily need to acclimatise to altitude but just gain adaptations associated with it (Wyatt, 2014).
The hormone erythropoietin (EPO) is responsible for stimulating the production of red blood cells in the bone marrow. It is released mainly by the kidneys and its magnitude is based on the level of hypoxia at the cell. Therefore, athletes at altitude have been shown to have an increase in EPO levels (Chapman et al., 1998; Saunders et al., 2009). A similar response was found with individuals suffering from sleep apnea (breathing stops) and elite free divers who have the ability to hold their breath for over 5 minutes (Choi et al., 2006; Schagatay, 2010). De Bruijn et al. (2008) found a significant increase of 24% in EPO concentration after repeated breath holds. These results would indicate that BHT can stimulate similar adaptations to altitude training. However, it is important to consider that the sample size was very small with only 10 relatively active participants. These results therefore might not represent the elite or sedentary populations.The results only show the short-term effect of breath holds so BHT might have different and potentially negative long-term effects. Also, more importantly these results only indicate an increase in EPO and not their endurance performance(de Bruijn et al., 2008).
The spleen is an organ that stores blood. This means that the size and contraction of the spleen will affect the release of red blood cells. It also responds to a hypoxia environment (Schagatay et al., 2020). Nepalese Sherpas have been shown to have an increased volume and greater contractions than Nepalese lowlanders, which indicates adaptation to the spleen associated to altitude (Holmström et al., 2020). Baković et al. (2003) found an increase in spleen contraction and a rapid decrease in spleen volume straight after 5 maximum breath holds. This would indicate that the spleen is releasing blood in response to the apnea (Baković et al., 2003). However, this only represents the initial response to apnea and does not indicate the long-term effect on the spleen volume and contractions. Bouten et al. (2019) actually found contrasting results after 8 weeks of BHT and saw an increase in the spleen volume, which would actually be an advantageous response as the spleen would have the ability to release more red blood cells. However, it also showed a decreased contraction of the spleen (Bouten et al., 2019). This may be because it is unnecessary to have a greater contraction because of the increase in volume. Therefore, it would seem that BHT also has a similar effect on the spleen to altitude training however again this does not necessarily transfer over to an improved performance.
When considering the effect on performance from breath holds, Sperlich et al. (2015) showed no improvement in cycling performance but an increase in spleen contraction after apnea-induced conditions. The results were tested on well trained cyclists and only had one exposure to breath holding as opposed to a period of BHT. Therefore, results could be different if tested after a period of BHT or within other populations where oxygen carrying capacity might be a bigger limiting factor to their performance. It is also important to consider that the distances were only 4km and therefore performance might have improved over longer distances (Sperlich et al., 2015). In contrast, Dimitrios and Geladas (2021) showed a11.7% increase in time to exhaustion on a maximum effort bike test after 2 weeks, every day of 5 repeated maximum efforts of apnea with 2 mins rest in between sets. However, again the sample size was very small, and the participants were only men. Also, account needs to be taken of the specificity of the cycling and the duration of the performance.However, similar results have seen with improved performances in swimming, which in some ways is understandable considering the swimming involves breath holds (Lavin et al., 2015). So far there has been no research showing the relationship between BHT and endurance running performance.
It is also important to consider potential negative effects of BHT. The first thing to consider about BHT is that it can be very unpleasant for the athlete and potentially increase stress and anxiety, which would have a negative effect on the performance (von Leupoldt et al., 2008). However, this may be no different to the uncomfortable feeling when training athigh intensities. More extreme or long-term issues such as headaches, lung damage or neurological harm could occur ifnot performed correctly and would need to be researched (Matsuo et al., 2014).
Summary
Although it seems that BHT does stimulate a similar response to altitude training through an increased production in EPO and adaptations to the spleen, which in turn can increase the red blood cell content and thereby the delivery of oxygen to the muscles, more research will need to be collected about BHT effects on specific endurance performance. Other adaptations to altitude training include an increase in capillary density and the concentration of aerobic enzymes, which will also have a dramatic effect on aerobic performance (Chapman, 2013; Saunders et al., 2009; Wyatt, 2014). However, these adaptations have not been researched with BHT. The method of BHT is not a new concept and has been practised for centuries, however it is only recently being scientifically researched. Therefore, further research should first focus on the long-term effect of BHT to see if there are any serious adverse side effects. It should then look at the specific effect son performance and lastly look to see if there are any other physiological adaptations associated with BHT (Harbour et al., 2022). If the method is safe to practise, then it could potentially be more effective than altitude training. This is because there would be a greater ability to control the volume and intensity of the hypoxia environment but also the ability to perform it anywhere. However, at present the optimal volume and intensity is unknown.
