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Did you know that the horse, generally regarded as one of the most robust animals on the planet, breathes almost exclusively through its nose? It is physically incapable of mouth breathing unless it suffers from an anatomical abnormality.
Though I learned that titbit after completing a majority of the research for this article, I think it is a testament that nature has designed mammals with an intent for optimal respiration through the nostrils.
The purpose of this piece is to investigate whether conscious nasal breathing during exercise, specifically that of the anaerobic type, might be beneficial over orinasal or mouth breathing in terms of performance and recovery.
Aerobic exertion relates to my findings as well.
Working out creates acidity. Acidity creates fatigue. Oxidation neutralizes acidity. Nasal breathing is better at oxidation than mouth breathing. Therefore nasal breathing should in theory reduce fatigue and speed recovery better than mouth breathing.
One of the penalties of kinetically induced metabolic excitation (i.e. exercise) is H+ and lactate production (the accumulation of which being more marked in the case of intense physical activity).
The build-up of these two by-products creates acidity which the body wants to balance by raising its pH back up to normal levels. Acidity also inhibits glycolysis, the process by which most energy is generated under anaerobic conditions. These factors contribute to the feeling of fatigue.
The path of least resistance for restoring pH is through hyperventilation, which by definition is when the body expels more carbon dioxide (CO2) than is produced. Hyperventilation typically occurs through the mouth (and not the nose).
However, a lower pH and higher concentration of CO2 foster more willing delivery of oxygen throughout the body, as per the Bohr effect. Oxidation by definition offsets reduction (i.e. acidity), and also converts lactate back into pyruvate, a building block of energy production.
By nasal breathing, CO2 is not dispelled as disparately and though airflow is constricted, limiting the rate at which oxygen can be assimilated into the bloodstream compared to mouth breathing, the oxygen that is inhaled is more efficiently distributed to fatigued tissues which should in theory improve athletic performance and recovery, with practice of the technique.
High intensity exercise, which often (but not always) recruits fast-twitch (aka type II) muscle fibres, stimulates glycolysis to synthesize ATP for energy in predominance over oxidative phosphorylation because glycolysis is able to produce ATP at a faster rate to fulfil acute energy demands, though oxidative phosphorylation is the preferential and more cost-efficient pathway of energy production within the body.
Fermentation (i.e. reduction) of pyruvate to lactate oxidizes NADH back to NAD+ for reuse in glycolysis. (Pyruvate and NAHD themselves are products of glycolysis.) NAD+ is available in limitation, hence the need to regenerate it.
Lactate is thus a by-product of glycolysis. Hydrolysis of ATP generated by glycolysis releases H+ which accumulates in the muscle along with the lactate.
Some of the H+ is buffered in the muscle and some diffuses into the blood in exchange for Na+ or along with lactate through monocarboxylate transporters (MCTs). This then decreases pH in the blood (because of the influx of H+ and plasma lactate, lowered HCO3– concentration, and thus increased amounts of CO2 from H2CO3 dissociation) and as a consequence, the body wants to raise its pH back up to maintain homeostasis. This acidity specifically inhibits phosphofructokinase, an enzyme that catalyses a key regulatory step of glycolysis, and also impairs the utilization of glucose. This is partly what causes fatigue and in a way shows the self-regulation of these mechanisms to protect the body from overexertion.
The path of least resistance for raising pH is by eliminating plasma CO2, which is vaporized in the alveoli and exhaled by the lungs. Its dismissal is hastened by hyperventilation, which happens primarily by breathing through the mouth.
This helps restore pH, though CO2 is essentially displaced as lactate is produced, which is undesirable as lactate is not as synergetic with oxygen in the way carbon dioxide is through the Bohr effect.
Another method by which pH can be levelled is consumption of the glycolytic by-products, which is advantageous because this produces energy. The protons can be used in cellular respiration and the lactate can be oxidized back to pyruvate for use in metabolic processes as well.
As a side note, I find the interconnection here rather elegant; the heart is able to utilize the built up plasma lactate for energy, which thus allows it to pump harder and increase blood flow to tissues that have a pressing need for oxygen.
Mouth breathing is advantageous over nasal breathing in that it allows for increased airflow, which lets an individual reach higher levels of exercise intensity presumably because of the combination of higher oxygen consumption and lower carbon dioxide retention, both of which help balance acidity. The cost of this is that it is inefficient when compared to nasal breathing due to the Bohr effect, which means energy is wasted to achieve similar results of oxidation and subsequently I would imagine fatigue sets in sooner as this is a stressful state of physiology. If maintained, CO2 concentrations will likely further deplete, making oxygen delivery even poorer, exacerbating the effect, suggesting this is a mechanism to be avoided when possible and used only for short durations.
Therefore nasal breathing is preferential for its energy efficiency which should in theory better promote oxidative metabolism of glycolytic by-products, increase available ATP, and thus lessen fatigue and speed recovery from athletic endeavours.
I believe there are a few simple takeaways to be gleaned from this science that can easily be applied to improve the efficacy of one’s training.
Consciously make an effort to breathe through your nose at all times, as in 24/7, to develop mastery of the nasal breathing technique.
During high intensity activity, allow yourself frequent breaks to fully regain control of your breathing and allow your heart rate to reset before continuing. Don’t keep pushing while you are winded.
Nasal strips can help improve airflow, which appears to be the limiting factor in the exercise intensity one can achieve solely through nose breathing. (That limiting of intensity could be construed as a positive, however.) Nasal resistance does actually reduce on its own during exercise, too.
First and foremost, this is undoubtedly a simplified view of energetic processes and I do not claim to have that deep a grasp on the subject matter. There may be mistakes in my understanding and presentation above.
Secondly, I think there is ample evidence that shows mouth breathing allows for a higher respiratory rate than nose breathing. Whether the influx of oxygen or exhalation of carbon dioxide is the more relevant factor, I am not sure, but the increased flow rate of mouth breathing does allow exercise to reach a higher intensity.
However, unless you are a professional athlete and your livelihood hinges upon you sucking for air while putting your body through extreme stress, then do it when necessary, but for the rest of the population, if you are reaching the point where you must breathe through your mouth, I think that’s a sign you are training too hard.
What I am unclear about here though is exactly how oxygen is utilized when mouth breathing becomes a necessity at maximal intensity. It is delivered less efficiently, and I would assume certain metabolic processes take priority over others in terms of needing that oxygen. I am guessing oxidative phosphorylation is preferential over lactate consumption in this situation, which might help explain the lactate paradox. This warrants further investigation.
Thirdly, by forcing nasal breathing during high intensity exercise, I have a feeling the body might be exposed to a more acute period of acidity as compared to mouth breathing because of the lower but more efficient ventilatory rate of nasal breathing. By mouth breathing, my hunch is that the body’s pH is restored more gradually as it is the less effective but more voluminous technique. There may be consequences associated with this, if my assumptions are correct.
At high altitude, there is a belief that red blood cell production is stimulated to compensate for the relative scarcity of oxygen in the air, and that this is the primary cause for performance gains associated with altitude training.
However, others postulate that the positive effects of altitude training are mostly due to other factors, such as an adaptation to a more economic utilization of oxygen. This claim seems to be supported by the lactate paradox, which shows “reduced production of lactic acid at a given work rate at high altitude.” Lactate levels should not be reduced if increased red blood cell mass was the predominant factor in performance increase because carbon dioxide plays such a role in oxygen delivery.
Building one’s tolerance of nasal breathing is probably comparable to physiological adaptations of high altitude.
Sodium bicarbonate (i.e. baking soda) raises blood pH which helps buffer acidic build-up, delaying the onset of fatigue. (Excessive acidity impairs energetic pathways.)
It also increases PCO2, allowing O2 to be delivered more readily to fatigued muscles because of the Bohr effect, though the increase in pH may initially offset the increase in carbon dioxide concentration, limiting the phenomenon.
As all this translates to aerobic exercise, the main principle still stands: nasal breathing improves the delivery of oxygen. Oxidative phosphorylation, the preferential metabolic pathway of the body, is more efficient than glycolysis and relies on O2 availability. Thus, sufficiently supplying an increased demand for oxygen during low intensity activity is important as well.
Those interested in endurance exercise may want to read about lactate threshold and note how it relates to oxidation.
Unmentioned here is that metabolic processes create heat. Thus when one exercises, extra energy is spent and body temperature rises. This typically is compensated for by the dissipation of heat through the skin to maintain a functional core temperature. When one’s internal temperature becomes too high, performance suffers (and the risk of serious biological harm onsets).
I have yet to delve deep into the literature on this subject matter, but as it relates to respiration, I think the goal is still ultimately to promote energy efficiency, and excessive heat retention should be viewed as the result of an obstruction, namely the temperature of the outside environment.
It is unclear if there is an optimal ambient temperature for which to exercise, but marathon results show a progression of improved performance all the way down to 41 °F. (Data presumably hasn’t been interpreted below that number.)
My guess would be that the lowest temperature one can tolerate without impediment of motor functioning is the best in terms of maximizing potential.
I am unsure about the relationship between respired air temperature and pulmonary gas exchange (it may again be influenced by the Bohr effect), but nasal breathing warms air better than mouth breathing, though tidal volume lessens with cold air. Glycogenolysis is also reduced at lower temperatures, suggesting improved oxygenation.
Alas, this is a topic for another day.
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