There’s exercise and then there’s Exercise with Oxygen Therapy (EWOT). As the name suggests, this involved performing some training while breathing in higher than normal levels of oxygen. This can be delivered either via a mask, or by hyperbaric chamber (a pricier option). Because it’s purported to provide superior benefits, it has become appealing to some with an interest in hacking their way to peak health. Of course, it’s not the first exercise-related hack people have come up with: for example, EMS training is also popular. Nor will it be the last. But if you want to know if EWOT is as promising as it sounds, read on.
- EWOT use has arisen from logical arguments, however the quality of the research is such that we can only say that EWOT may provide benefits to performance. Until the body of research is based on larger studies of representative populations, with consistently strong methodologies, a definitive position will be unattainable.
- Our limited body of evidence currently suggests that, during a single exercise session, EWOT can increase endurance, allow you to complete a set amount of work in a shorter time, and improve dynamic muscle function. The impact it has on your maximal intensity/power output currently appears more questionable. Your results could also vary depending on how fit you are to begin with.
- Use of oxygen therapy during recovery appears to be only modestly beneficial.
- There are very mixed results regarding the long-term impact of EWOT on various aspects of fitness, including power output, maximum oxygen consumption, endurance, blood lactate dynamincs.
- Any EWOT use should be supervised by a medical practictioner, as there is actually such a thing as oxygen toxicity.
Why the interest in EWOT?
Extrapolation from scientific observations accounts for some of the interest in EWOT. For example, low levels of oxygen have been observed in the arterial blood of endurance athletes during very intense work. Logical theories suggests that increasing the oxygen levels of blood will allow more of the good stuff to be delivered to working muscles, and therefore improve performance. It has also been experimentally observed that the capacity of the mitochondria to use oxygen to create energy is greater than our capacity to deliver oxygen to the muscles… in normal atmospheric conditions. Thus, in EWOT, the oxygen content of air breathed is increased beyolnd the normal 21% (also referred to as hyperoxic air).
There are three main groups who use Exercise with Oxygen Therapy: people who are ill; athletes; and other people who simply wish to maximise their exercise performance or otherwise optimise their health. We’re going to focus on the latter users, but let’s briefly dip into EWOT for clinical populations…
EWOT for managing disease
Most clinical research focuses on people who suffer from chronic obstructive pulmonary disease (COPD), with some examination of coronary artery disease (CAD) thrown in. Alas, a 2020 systemic review and meta-analysis showed that among people with these conditions, long-term use of EWOT is not effective at improving exercise performance- whether measured by maximum oxygen consumption (VO2max), power output or distance people covered in a 6 minute walk test. However, we don’t actually have enough evidence to warrant giving up on it as a potential adjunct therapy just yet… Out of the 4038 articles the authors identified, only 11 were deemed eligible for inclusion in the analysis. Thus we need more high quality studies. Ideally this research would also provide us with information regarding what doses of EWOT are required to maximise the long-term benefits. We could also use studies examining its value to other conditions.
Back to EWOT for apparently healthy people…
What impact does EWOT have on exercise performance?
Acute performance benefits of EWOT
Based on the observation that low levels of oxygen in the blood can limit performance, it is argued that using oxygen therapy during exercise can acutely boost your performance. Is this logical? Sure. Is it true? Not sure… there is some evidence to that effect- but not enough to make definitive conclusions. A 2018 meta-analysis of studies suggested that breathing air containing 30+% oxygen tended to be substantially beneficial to endurance; completing a set amount of work in less time; and improving dynamic muscle function. However, on the whole it didn’t appear to improve the maximum intensities one can work at.
Other individual studies have suggested that it might lead to slight improvements in power output and tolerance of HIIT training. Yet another small study from 2010 suggests exercise tolerance might only be enhanced when it lasts for more than four minutes- and it may even slightly lessen tolerance to shorter training bouts.
If these findings are accurate, it means that the impact varies depending on what measure of fitness you wish to improve. However, marked differences between studies to date, and the fact that most studies are of small sample sizes, mean we cannot even be certain of these findings.
For the sake of less clarity: a small study from 2017 suggests that the impact of EWOT may also depend on your baseline fitness. That is, those who start with a high level of aerobic efficiency seemed to benefit more. Further examination of this possibility- along with the rest of it- should be carried out.
Possible mechanisms for any benefit (as gleaned from small studies) include:
- Increased amount of oxygen carried by haemoglobin in the blood- or an attenuated decline during exercise.
- Increased uptake of oxygen by mitochondria
- A shift in fuel usage. In a 2017 study of 14 men and 4 women, the amount of fat burned for fuel increased by 52%- while carbohydrate usage decreased.
- Reduced relative stress of a workload. In an early study, when hyperoxic air was used there was less demand for ventilation, and lower levels of adrenalines and lactate were seen in the blood. It also allowed the participants to produce higher power for the same amount of physiological stress as when breathing room air. This study only used 5 participants though, so like most individual studies in this field, it needs to be taken with a grain of salt.
- Shifts in muscle metabolism responses. In a 2010 study of 7 people performing maximum knee extensions, the levels of phosphocreatine within muscle fell more slowly when hyperoxic air was breathed. Phosphocreatine helps maintain a cell’s supply of ATP, and thus is essential for muscle contractions.
- It may prevent extra oxidative stress associated with the increased aerobic metabolism required for higher speed and power output. At least, there were lower levels of inflammatory markers seen among 19 trained male cyclists completing interval training with oxygen therapy. However, the study was also conducted at moderate altitude (1800-1900 m), which may have shaped these results. In addition, those of us who aren’t as well trained as these men may not have the same response.
Much more evidence is required to turn these from vague hypotheses to something like a fact.
What about using EWOT during recovery?
The above mentioned 2018 meta-analysis suggested that using oxygen therapy during recovery is only modestly beneficial.
You will see below that there are contradictions between the results of different studies. Another problem we have is that the rate of clearance of lactate from the blood is often used as a key measure- whilst the assumption that it is a good indicator of recovery is fraught with problems. It is also uncertain whether blood lactate clearance has a material effect on performance. Thus, we need more research to clarify what the best indicators are, and then to explore those more robustly.
So I suppose I could skip this next chunk of info- or you can choose to do so. But, in the interest in sharing what we do have:
One study of 10 well trained cyclists found that breathing hyperoxic air during six minute rest intervals between five, 30-second bouts of maximum work provided no more benefit than room air. That is, it didn’t boost either average or peak power output. There was also no effect on blood lactate concentration, pH or base excess (which are taken as reflective of metabolic shifts).
Another small study showed that even breathing 100% oxygen during a 5 minute recovery from a single maximal cycling effort provided no benefit in terms of clearing lactate from the blood. The author noted that longer usage was not attempted, as there is risk of oxygen toxicity (see more about this below). In contrast, an early study demonstrated a faster restoration of phosphocreatine levels when 100% oxygen was breathed during rest.
A couple of early studies suggest that the capacity of oxygen therapy used during recovery intervals to clear blood lactate may depend on both an individual’s baseline fitness and the exercise intensity. Participants were split into two groups based on fitness. They found that the fitter people’s blood lactate clearance was significantly increased when air consisting of 60+% of oxygen was used in recovery. Meanwhile, the less fit benefited from 30-40% oxygen when they performed at intensities over 65% their maximum oxygen consumption, but not less.
The chronic effects of EWOT on exercise capacity
The long-term effects of exercising with hyperoxia are also inconclusive- possibly moreso than the acute effects! Perhaps we can blame the complexity of physiological responses to hyperoxia and differences between studies for this.
It may or may not have beneficial effects on different aspects of fitness:
- Power output: there are mixed results. A number of small studies suggest that repeated high-intensity or interval exercise with oxygen therapy can increase power output. For example, a 2005 study found that recreationally active people increased their power output by 8.1% after 6 weeks of high intensity cycling training, using 60% oxygen. However, in a 2012 study training with normal air actually increased power output more than hyperoxic air.
- Peak/Maximum Oxygen consumption: Most studies I came across suggested that EWOT doesn’t boost oxygen consumption any more than normal training, or at least has no significant effect. One four-week study among well trained cyclists even suggested breathing normal air was more effective.
- Blood lactate dynamics: In a 2020 study a group of athletes performing HIIT with EWOT for 3 weeks allowed them to increase their intensity with slower increases in blood lactate levels. In contrast, in a 2012 study normal air was more effective at increasing the lactate threshold (the point at which lactate starts accumulating in the blood, because your body can’t keep up with it…)
- Endurance: In 2005 and 2007, small studies on recreationally active people showed that using 60% oxygen over 6 weeks of training lead to greater increases in the amount of time they were able to work at 90% of their maximum oxygen consumption, compared to the same exercise protocol with normal air. In contrast, there appeared to be no difference between the endurance or muscle function of 17 moderately trained people undergoing 5 weeks of training, whether they breathed air or 80% oxygen. A recent study of 23 trained cyclists showed only an insignificant improvement in self-paced endurance, and no improvement in exercise efficiency even after completing a 6 week hyperoxic training program involving both HIIT and steady state exercise
- Metabolic enzymes: In the above mentioned 2007 study, pre- and post-training muscle biopsies showed no significant difference in changes to metabolic enzymes whether normal air or hyperoxia was used.
- Oxygen carrying capacity of blood: This is possibly unchanged, based on a recent study showing no extra benefit of chronic hyperoxic training on blood volume or haemoglobin mass
- The capacity of mitochondria to generate more ATP through aerobic metabolism: This also appears unchanged from this recent, albeit small study
Larger, more robust studies with greater statistical power would not go astray.
Are there risks to EWOT?
It is actually possible to take in excess oxygen so that it becomes toxic. For example, hyperoxia may generate reactive oxygen species. When there are too many of these (so that they overwhelm your antioxidant defences), the alveoli of the lungs may suffer irreversible damage (eg: they may become too permeable, there could be unwanted collagen deposition).
The variables which could affect your risk are beyond the scope of this article. Any EWOT use should be guided- and closely supervised- by a medical practitioner.
The evidence is more equivocal. It seems breathing hyperoxic air may improve some measures of performance during a single exercise session, and that if used during recovery it may be modestly beneficial. Based on the data we currently have, we can’t bank on obtaining any greater benefits from chronic use than what you’d get from habitually performing plain old exercise. Sure, it may be a more valuable tool than we know… But we’d require much larger, more rigorous studies of representative populations, including non-athletes, to prove that it is worth your time and money. If you wish to try your luck with it despite the lack of evidence, make sure to do so under medical supervision to minimise risks.
Have you tried EWOT? If so, feel free to share your experiences!
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