Does the way we breathe during exercise affect our performance? I think most of us probably don’t think too much about it, when we’re mid workout, gasping for breath, we’re just doing everything we can to keep moving. For elite competitors however, for those fighting for that extra 1%, these kinds of considerations can be extremely important. I’ve noticed a few high-level athletes discussing different breathing techniques recently. One of the main techniques which seems to be in vogue is nasal breathing, with some employing it during the marathon row at the CrossFit Games this year.
Since breathing is my Specialty, I thought I would dive into the literature and try and discover whether there is actually any science behind the claims that nasal breathing improves athletic performance.
How do we normally breath during exercise?
There is wide variability between how people breath, both at rest and during exercise. Most people either breathe through both their mouth and nose during rest and exercise, or switch from nasal breathing at rest to mixed breathing during submaximal exercise (1, 2).
What are the supposed benefits of nasal breathing?
- Filtering, warming and humidification of air
- Increased inhalation of nitric oxide causing increased oxygen uptake in the lungs
- Reduced exhalation of carbon dioxide and increased oxygen uptake by tissues
Ok, so lets take these points one at a time and look a bit more closely.
Filtering, warming and humidification of air
One of the main functions of the nose is to filter, warm and humidify air. It has tiny hairs which filter particles as air passes by them. The nose also warms and humidifies air via the nasal turbinates. These increase the surface area for blood vessels in the nasal mucosa to warm and allow the evaporation of water into the air.
At rest, when breathing through our nose, gases reach a temperature of 36°C (almost matching body temperature) and a relative humidity of 80-90%. This reduces heat and water loss from the body. When breathing through the mouth, this humidity is reduced to 70%. So, in this sense nasal breathing does appear to be beneficial. Further so when we consider that cold air and dust particles can be triggers for conditions like asthma (3).
Increased inhalation of nitric oxide causing increased oxygen uptake in the lungs
Nitric oxide is a chemical produced in the body that causes dilatation of the blood vessels. It is found in the walls of these blood vessels, where it is released in response to triggers like trauma. For example, when a doctor taps on a vein through the skin, nitric oxide is released, and the vein dilates, becoming more prominent, and allowing them to take a blood sample more easily.
Nitric oxide is also produced in the sinuses of the nose (paranasal sinuses). Therefore, the theory goes that by breathing through the nose, more nitric oxide is inhaled and travels down into the lungs, causing dilatation of the blood vessels within the lungs and therefore allowing more oxygen to pass from the lungs into the blood.
Now this sounds great, but this is also where it gets a little confusing. A number of studies have shown that nitric oxide production is reduced during exercise, and not just because we are breathing more air so the levels become diluted. This decrease is attributed to a reduction in blood flow to the paranasal sinuses during exercise, and therefore decreased delivery of the substances needed to make and release nitric oxide (4, 5, 6).
On the other hand, some studies have shown that nitric oxide production is actually increased during exercise (7) . Others have shown that production is increased, but that this increase is from within the lungs, and not from the paranasal sinuses (8). Another study shows that production is reduced during exercise in sedentary subjects, but increased in athletes (9).
I know what you are thinking, how can some research show one thing and others show the total opposite? Unfortunately, this is not a particularly well researched area and all of these studies have been carried out with very small numbers of participants, leaving them prone to error and bias.
Perhaps most importantly, a study done in Japan showed an increased production of nitric oxide during exercise, and increased further in nasal breathing, however there was no effect on any other physiological parameters i.e. it did not improve performance (10).
Nitric oxide is a very clever little molecule, and may also have some dilating effects on the airways themselves, allowing us to breathe more easily. There is evidence of this effect in asthmatics, however nitric oxide has not been shown to have this effect in healthy subjects (11).
Reduced exhalation of carbon dioxide and increased oxygen uptake by tissues
This is where we dive a bit deeper into the physiology, so bear with me. This idea is based on a phenomenon called the Bohr effect. Oxygen is normally carried in blood by a substance called haemoglobin. Carbon dioxide and heat are produced by active tissues which are using oxygen to create energy, for example skeletal muscle during exercise. When the blood reaches these muscles, the carbon dioxide and the increase in temperature cause the haemoglobin to change shape and release the oxygen that it is carrying.
Carbon dioxide also increases cardiac output (the amount of blood pumped by the heart per minute) and causes dilatation of blood vessels, improving blood flow.
When we start exercising, these things all start happening as a reflex response. We exercise, so we make more fuel in the muscles, so we produce more carbon dioxide in these muscles. This carbon dioxide causes dilatation of the blood vessels supplying the muscles, so we get more oxygen arriving, and the haemoglobin releases more oxygen when it gets there.
The question is, can we enhance this Bohr effect by breathing nasally, which reduces our minute ventilation (volume that we breathe per minute), and thereby reduces the amount of carbon dioxide that we breathe out during exercise?
A study of nine individuals performing a cycle test under nasal and oral breathing showed that nasal breathing did reduce hyperventilation, however there was a compensatory increase in heart rate under these conditions, implying increased cardiovascular stress, and there was no difference in power output or performance measures between the two (12).
A study of twenty healthy patients showed a reduction in minute ventilation in nasal breathing, but also showed a decrease in maximal oxygen consumption (14).
A study of nineteen healthy subjects compared nasal and oral breathing at 50%, 65% and 80% of their VO2 max. This showed reduced oxygen consumption during nasal breathing at all intensities. This result alone implies that perhaps nasal breathing is more efficient, given that the two results are at the same intensity. However, in the 80% intensity group, the oxygen saturation of haemoglobin was significantly lower in the nasal breathing group, implying a reduced oxygen delivery to tissues. Therefore the study team calculated the oxygen cost of the exercise and compared it to the oxygen consumption. In 13/57 measures, nasal breathing oxygen consumption did not meet the oxygen cost, whereas in all measures oral breathing exceeded it. For the exercise to be completed without consumption meeting cost, there must have been other physiological compensations contributing to the nasally breathing group- there must have been contributions from anaerobic pathways (13).
There is one study however, which used runners who had practiced nasal breathing in training and racing for at least six months prior to being tested. The results showed no loss in VO2 max between nasal and oral breathing, with an improved physiological economy (energy expenditure) in nasal breathing (15).
So what does all of this mean?
There is a lot more to this topic than the overview that I have covered here. The physiology involved during exercise is a vast, complex and not hugely well researched subject. I think we can safely say that currently there is no strong evidence that nasal breathing helps improve athletic performance in healthy subjects. However, I don’t think we can say that it is definitely detrimental either. In those suffering from exercise induced asthma, it may well be beneficial. As with all aspects of training, it seems that practicing nasal breathing is probably an important factor. Overall, I think this is a really interesting area of exercise physiology, with a lot more research needed to provide some concrete answers.
I would love to hear from you, please leave comments or questions below and if you have any ideas for other topics that you would like me to cover please let me know!