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Nasal breathing and the balance of blood gases during exercise

The nose is a vital part of the respiratory system. It warms and filters air as it enters the body, protecting the airways against inflammation and irritation. In order to appreciate the difference this makes to your breathing, it’s worth understanding what happens when you inhale cold, dry air straight into your lungs. In one study, scientists compared the nasal response to exercise in people who were wearing nose clips, making them mouth-breathe by default. Participants were tested for bronchoconstriction (tightening of the smooth muscle in the lungs that causes wheezing, coughing and breathlessness) in various conditions during exercise. It was found that when they breathed dry, cold air, they suffered exercise-induced bronchoconstriction, but when they breathed warm humid air, their airways remained clear2.

The nose creates resistance that allows the body to use inhaled air more efficiently. Nose breathing results in a 10 to 20 percent greater oxygen uptake in the blood. When you breathe, your lungs exchange and metabolize oxygen and carbon dioxide. During exercise, your body uses more oxygen, so the concentration of oxygen in the blood drops. The increased muscle activity and metabolic rate mean you produce more carbon dioxide. What will normally happen is that your breathing speeds up relative to your CO2 production – CO2 leaves the body in expired air – so your blood carbon dioxide levels shouldn’t change much. However, if your CO2 levels become too high, the speed and volume of breathing will increase and heart rate becomes faster. All of this makes it quite hard to continue training. Therefore, your ability to sustain physical exercise is directly related to your blood sensitivity to CO2.

When your chemoreceptors (breathing receptors) are very sensitive to blood carbon dioxide, your breathing is likely to be quicker and from the upper chest. On the other hand, when you develop a lower sensitivity to CO2, your breathing will stay quite light during rest, and even during exercise within a certain intensity and duration. For this reason, low sensitivity to CO2, or a low hypercapnic drive, is advantageous for sporting performance and stamina, and for general levels of health. In fact, research has shown that low sensitivity to CO2 is one factor that sets outstanding endurance athletes apart from their less successful rivals3.

As far back as 1979, scientists were exploring this relationship between low sensitivity to CO2 and exceptional athletic performance in endurance sports4. And in 2007, a study by the biologist and physical education expert, Xavier Woorons, found that reduced sensitivity to blood CO2 was responsible for lower rates of respiration in trained men at sea level and during altitude simulation5.

While it is believed that the desire to breathe, as triggered by blood CO2 levels, might be lessened by intense physical training3, the truth is, not many people are in a position to train to the necessary levels to achieve this. However, the exercises in the Oxygen Advantage are designed to reduce your ventilatory response to blood carbon dioxide. The BOLT score, which is a measure of functional breathing, is also an indicator of your sensitivity to CO2 build up.

Using nasal breathing to improve performance

Since nose breathing produces more efficient oxygenation, it makes sense that it is preferable to breathe through the nose. Scientists have shown that nasally restricted breathing can be used during training to improve endurance6, stamina and performance, especially where economy is a key factor. In 2018, Dr. George Dallam, professor of exercise science, triathlete and coach to some of the world’s top athletes, published a study that examined the potential of nasal breathing in sport. His subjects were ten recreational runners who had raced and trained using only nose breathing for six months in the run-up to the experiment. Most people breathe through their mouths during rigorous exercise, switching to mouth breathing when their breathing volume reaches around 40 liters a minute. This is because mouth breathing creates less resistance, and so it’s easier to take in more air more quickly through the mouth, which is an instinctive response to feelings of air hunger7.

In Dallam’s study, participants were tested after six months using only nasal breathing, which meant their bodies had adapted to the practice. Results were taken when subjects breathed only nasally, and only through the mouth. Just like in the study that examined bronchoconstriction, default mouth breathing was ensured by asking each subject to were a nose clip. The results showed that:

  • Breathing rate was much slower during nasal breathing than oral breathing. When the athletes nose-breathed during running, they took 39.2 breaths per minute, compared with 49.4 breaths per minute in oral breathing
  • The percentage of carbon dioxide in expired air, called end tidal carbon dioxide, was much higher in the nose breathing trial (44.7mmHg compared with 40.2mmHg in mouth breathing)
  • End tidal oxygen pressure was lower when participants nose-breathed. Less oxygen in expired air means that more of the inhaled oxygen is being absorbed into the bloodstream
  • Speed of breathing was 22% lower in when breathing was through the nose

The results of the study also indicated that after six months exercising using only nasal breathing, the runners were able to achieve the same optimum oxygen consumption when they were mouth breathing. This is thought to be because the nasal breath training had enabled them to develop slower breathing patterns. Slower breathing gives extra time for oxygen to diffuse into the bloodstream, as air is pulled deeper into the lungs and stays there longer. The 22% reduction in breathing speed also represents easier, less effortful respiration7.

The results of Dallam’s study suggest that the body adapts to nasal breathing by developing an increased tolerance to changes in blood CO2, lessening air hunger. They also show that it is possible to maintain VO2 max and peak performance following a period of training using only nasal breathing, and that nasally restricted breathing during training may be beneficial for endurance athletes who want to boost their performance and maintain good respiratory health7. This is coherent with findings of previous research, which demonstrated that air hunger could be lessened by using exercises to increase end tidal carbon dioxide and push feelings of air hunger beyond normal ‘comfortable’ levels8.

Respiratory muscle training

During intensive exercise, the breathing muscles have a significant rising oxygen demand in line with the increase of speed and volume of breathing (hyperpnoea)1. These respiratory muscles are at risk of fatigue, especially during endurance sports. As the breathing rate and volume increase during near maximal exercise, blood flow to the legs is significantly altered1.

The body’s sensitivity to blood carbon dioxide also has an impact on the work of the respiratory muscles during exercise. If your BOLT score is low, you will breathe harder when exercise intensifies. Breathing hard requires a lot of work from the respiratory muscles, and as these muscles become fatigued, blood is diverted from the legs to support breathing9. This redistribution of blood away from the working muscles is called metaboreflex. It makes your legs feel tired, forcing you to slow down or stop. When the respiratory muscles overwork, metabolic by-products like lactic acid collect in the tissues, causing reduced circulation of blood. However, studies into breathing techniques have demonstrated that when the effort of inhalation is lessened, blood flow to the legs improves by as much as 7%9.

In order to develop and strengthen any muscle in your body, it is necessary to work that muscle harder than normal. But it is difficult to improve strength in the breathing muscles, even through regular high-intensity workouts. It’s simply not possible to sustain a high enough level of exercise for long enough to make a difference. Nasal breathing helps here as it engages the diaphragm, while mouth breathing tends to be from the upper chest.

The breathing muscles fall into two groups – inspiratory muscles and expiratory muscles. The inspiratory muscles are used during inhalation. These work much harder than the expiratory muscles, as expiration is relatively passive. They are therefore more at risk of fatigue. One way to train these inspiratory muscles is to practice inhaling against resistance. While the nose already provides more resistance than the mouth, you can extend the practice beyond just nasal breathing by using a resistance mask like the SportsMask, which has an adjustable valve opening. This valve provides the mechanism for conditioning the respiratory muscles, in the same way as any other progressive muscle training program. The technique is called IFRL or inspiratory flow resistive loading. IFRL can increase the strength of your breathing muscles by up to 50%.

Another way to develop strength in the breathing muscles is by using the exercises in the Oxygen Advantage that simulate high-altitude training. The practice of breath holding after a normal exhalation creates an air hunger and causes changes in the acid-base balance of the blood. During the breath hold, the body can’t remove excess carbon dioxide from the lungs, and so the cells continue to work to diffuse oxygen. The result is a combination of high blood carbon dioxide – called hypercapnia – and low blood oxygen – called hypoxia. The diaphragm sends messages to the brain to resume breathing and restore normal blood gas levels. These messages become more urgent as the breath hold continues, and the diaphragm begins to contract again and again. This effectively constitutes a workout for the diaphragm muscle, which is the main muscle of the respiratory ‘pump’.

Air hunger training for athletic performance

Carbon dioxide provides the primary stimulus to breathe in. Nasal breathing during sport makes you breathe slower and take in less air. This creates an increase in blood carbon dioxide, which in turn means better oxygenation of the working muscles, including the respiratory muscles.

This is all very well in theory, but when exercise becomes intense, it’s pretty hard to keep nose breathing10. Unless you’ve been training your breathing for a minimum of 6 to 8 weeks, you’ll experience strong air hunger as exercise intensifies, and you’ll want to switch to mouth breathing. The switching point in terms of minute ventilation differs from person to person. It depends on factors including the size of your nose, your metabolism and your tolerance to blood CO2, but by the time the volume of air entering your lungs reaches about 35 or 40 liters, you are likely to begin breathing through your mouth11. Mouth breathing is faster and helps you take in a larger volume of air, hence it feels more comfortable past a certain intensity of exercise. The larger volume of air causes blood CO2 to drop, lessening your feelings of air hunger7. If, instead, you continue to breath through your nose, your lungs will extract more oxygen from the air you breathe, lessening your feelings of air hunger through better oxygenation. Of the two options, the second is the more efficient. Once your body adapts, this increased efficiency makes it much easier to maintain nose breathing during more intense exercise. If you practice only nasal breathing for six to eight weeks, your feelings of air hunger will subside.

In order to reduce your feelings of air hunger during exercise, work to increase your BOLT score and practice exercises to develop slow, light and deep breathing. This means:

  • Fewer breaths per minute
  • Breathe only as much air as you need, don’t over-breathe
  • Breathe from your diaphragm, not into your upper chest

Suggestions during running for recreational athletes

If you are in good health and exercising regularly in order to improve your aerobic fitness, you should aim to breathe nasally throughout your workout7. Try to maintain nose breathing all the time. If you feel like you aren’t getting enough air and need to switch to mouth breathing, slow down and allow your breathing to normalize before resuming exercise.

Suggestions during running for competitive athletes

Competitive athletes will need to use nose and mouth breathing at different times during training and competition. During your warm up, nasal breathing combined with breath-holding exercises can be beneficial.

Practice slow, light, deep breathing as part of your warm-down. The kind of high-intensity training needed to maintain muscle tone will require mouth breathing. During lower intensity training, you should breathe only through your nose. With this as a guideline, you may spend around 50% of your training breathing nasally. It is possible to breathe through your nose during intense exercise, even if it’s not always comfortable to do so. In fact, scientists have proven that healthy adults can maintain nose breathing to 85% of VO2 max12.

When you’re competing, there’s no need to deliberately take bigger breaths to get more oxygen. Instead, work to develop a higher BOLT score and your breathing will be naturally more efficient

References

1. Sheel, A. William, Joshua Landen Taylor, and Keisho Katayama. “The hyperpnoea of exercise in health: Respiratory influences on neurovascular control.” Experimental Physiology (2020).

2. Strohl, KINGMAN P., MICHAEL J. Decker, LESLIE G. Olson, T. A. Flak, and PETER L. Hoekje. “The nasal response to exercise and exercise induced bronchoconstriction in normal and asthmatic subjects.” Thorax 43, no. 11 (1988): 890-895.

3. McGurk, S. P., B. A. Blanksby, and M. J. Anderson. “The relationship of hypercapnic ventilatory responses to age, gender and athleticism.” Sports medicine 19, no. 3 (1995): 173-183.

4. Martin, BRUCE J., KENNETH E. Sparks, CLIFFORD W. Zwillich, and JOHN V. Weil. “Low exercise ventilation in endurance athletes.” Medicine and science in sports 11, no. 2 (1979): 181-185.

5. Woorons, X., P. Mollard, A. Pichon, C. Lamberto, A. Duvallet, and J‐P. Richalet. “Moderate exercise in hypoxia induces a greater arterial desaturation in trained than untrained men.” Scandinavian journal of medicine & science in sports 17, no. 4 (2007): 431-436.

6. Joyner, Michael J., and Edward F. Coyle. “Endurance exercise performance: the physiology of champions.” The Journal of physiology 586, no. 1 (2008): 35-44.

7. Dallam, George M., Steve R. McClaran, Daniel G. Cox, and Carol P. Foust. “Effect of Nasal Versus Oral Breathing on Vo2max and Physiological Economy in Recreational Runners Following an Extended Period Spent Using Nasally Restricted Breathing.” International Journal of Kinesiology and Sports Science 6, no. 2 (2018): 22-29.

8. Bloch-Salisbury, Elisabeth, STEVEN A. Shea, R. O. B. E. R. T. Brown, Karleyton Evans, and Robert B. Banzett. “Air hunger induced by acute increase in PCO2 adapts to chronic elevation of PCO2 in ventilated humans.” Journal of Applied Physiology 81, no. 2 (1996): 949-956.

9. Amann, Markus. “Pulmonary system limitations to endurance exercise performance in humans.” Experimental physiology 97, no. 3 (2012): 311-318.

10. Saibene, Franco, Piero Mognoni, Claudio L. Lafortuna, and Richard Mostardi. “Oronasal breathing during exercise.” Pflügers Archiv 378, no. 1 (1978): 65-69.

11. Niinimaa, V. P. S. R. J., P. Cole, S. Mintz, and R. J. Shephard. “The switching point from nasal to oronasal breathing.” Respiration physiology 42, no. 1 (1980): 61-71.

12. Thomas, S. A., V. Phillips, C. Mock, M. Lock, G. Cox, and J. Baxter. “The effects of nasal breathing on exercise tolerance.” (2009).c


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