Breathing for runners – Part 1

PART 1: Breathing Functions and Limitations During Running

(Many thanks to MFV, PhD and multi-bostonian for proofreading this article)

If you only have a few seconds:

When running, energy expenditure and locomotion speed increase. Respiratory rate and volume adapt in response to produce energy. Beyond the metabolism, the respiratory chain facilitates locomotion. In some cases related to a weakness or misuse of the respiratory chain (hyperinflation of the lungs, blood stealing, hyperventilation), breathing can be limiting and cause breathlessness.

If you have a few minutes, read on…

Breathing control is potentially beneficial for anyone who is subject to constraints that can impact their stress level, their emotions, their posture. This concerns almost everyone. But more fundamentally, breathing is a physiological response to energy needs. Physical activity implies an increase in energy needs (in addition to impacting stress, emotions and posture). It is therefore easy to understand that the control of breathing can be crucial for sports practice. One can only hope that this involves as many people as possible, given the benefits of physical activity (Kandola et al., 2019; Mok et al., 2019; Reimers et al., 2012). One popular physical activity is running. In fact, there was a time when I used to run a lot. On the road, on the trail, three times a week at least. In sessions of five, ten, twenty and even forty kilometers. I liked it a lot. That’s why, when I read about breathing in relation to sports, I am particularly interested in running, compared to sports I have never played, like golf or curling.

Therefore, it was with great interest that I read the recent article by Harbour et al. on respiratory tools that can be used to improve running (Harbour et al., 2022). This article presents a state of knowledge on breathing during physical activity in general and running in particular. More specifically, it presents the conditions under which breathing can become a limiting factor. Secondly, the article discusses breathing tools that could move these limits and improve practice.

The goal of this two-part blog post is to provide a summary of the Harbour et al. article that is accessible to as many people as possible while remaining as accurate as possible. My hope is that as many running enthusiasts as possible can access this knowledge without necessarily mastering the science and jargon associated with it¹.

Rather than presenting the breathing tools right away (which I will reserve for a second part), I felt it was important to take the time to also summarize the basics of breathing during sport and the problems that can arise. This is the objective of this first part. This approach, I hope, in addition to respecting the methodology of the authors of the original article, will convince running enthusiasts of the validity of the tools. I have taken the liberty of making a few personal comments.

Breathing while running

Breathing as a metabolic response

Respiration is a cellular process of energy production. The balance is the transformation of glucose (C₆H₁₂O₆) and oxygen (O₂) into carbon dioxide (CO₂), water (H₂O), and energy in the form of ATP. During physical activity, the body’s energy needs increase. Respiration increases in response to these energy needs. How does respiration increase? At the organism level, this is manifested by an increase in ventilation. Ventilation is the speed and amplitude at which you inflate your lungs. Increasing ventilation will provide the cells with more O₂ while getting rid of CO₂, thus ensuring energy production. During physical activity, the volume of air breathed per minute can increase from 6 L/min to 150 L/min. This parameter, called minute ventilation, is itself broken down into respiratory frequency (number of respiratory cycles per minute) and respiratory volume (liters of air ventilated during a respiratory cycle). Physical activity can therefore cause an increase in respiratory rate, respiratory volume, or both. When physical activity is initiated, it appears that the increase in respiratory rate is the initial adaptation and the increase in respiratory volume is more gradual². This balances out with the effort according to the “principle of minimal effort”. The respiratory rate increases to 35-70 breaths per minute (compared to 12-20 at rest, for more information on the respiratory rate, I refer you here) and the respiratory volume to 50-60% of the vital capacity (compared to approximately 13% at rest, N.B.: the vital capacity corresponds to the “usable” lung volume). Beyond minute ventilation, other changes occur when physical activity increases. Typically, there is a shift from nasal to oral breathing when the threshold of 40 L/minute is exceeded. In addition, the ratio between inspiratory and expiratory times is altered. Slightly, in favor of expiration at rest, it balances or even favors inspiration during physical activity³.

Respiration as an aid to locomotion

The previous aspects concern the respiratory response to energy needs, in this case to metabolism. But breathing is connected to the locomotor system, with which it is synchronized. This synchronization concerns not only the frequencies (synchronization of respiration/minute and step/minute frequencies), but also certain phases of ventilation and movement (such as the synchronization between the impact of the step and the end of expiration). It is observed in many animals. Running consists precisely in increasing the activity of the locomotor system. It is therefore easy to imagine that ventilation-locomotion synchronization can be affected by such activity. Unlike quadrupeds, humans, because of their bipedalism, have greater freedom to modulate this synchronization. Ventilation-locomotion synchronization seems to occur naturally as soon as a rhythmic physical activity is set up (walking, running, rowing, etc.). Running presents some rather specific aspects of this synchronization. For example, the “visceral piston” model describes how the abdominal viscera move and drive the movement of the diaphragm during running. If the steps and breathing are synchronized, the visceral piston will assist the diaphragm. Conversely, without synchronization, the diaphragm would have to expend additional energy to ensure its movement. Assisted by the arms accompanying the movement of the stroke, this visceral piston can contribute 10-12% of the minute ventilation. It appears that this synchronization occurs relatively spontaneously, but can be refined by intensity, speed of movement and training.

When breathing limits running

As we saw earlier, breathing increases in intensity in response to physical activity in order to meet the energy demand. This process is unconscious and works very well overall. However, there are situations where the respiratory system is limiting, for example in high intensity (above 80-85% of VO_2max), in specific external conditions (hypoxia at altitude, climates that are too wet or too dry). But it should be noted that, despite good health and moderate intensity, between 20 and 40% of runners experience a sensation of breathlessness. This is called exercise-induced dyspnea. This phenomenon limits physical performance, which creates a negative psychological state that reinforces the sensation of breathlessness… and these three components (breathlessness, reduced performance, negative psychological state) reinforce each other. The authors of the article summarized here formulate the hypothesis that, apart from a particular pathological state, most experiences of breathlessness induced by exercise originate (at least in part) in suboptimal or dysfunctional breathing, and describe three dysfunctions of the respiratory system during physical activity.

Hyperinflation of the lungs

The increase in ventilation during physical exercise can induce a relative obstruction of the larynx, by principles of physics, such as Bernouilli’s principle. This is particularly problematic during high-intensity exercise, but up to 20% of athletes may experience this at moderate intensity (especially in elite athletes, women, adolescents and overweight individuals). This phenomenon can be favored by a dominant thoracic breathing and a hypertonicity of the abdominal muscles (which hinders the abdominal breathing and favors the thoracic breathing). This obstruction will disturb the air flow and can cause a phenomenon of “stacking of the respiratory cycles”: the inspirations take over the expirations, not allowing the lungs to return to a basic volume. This leads to hyperinflation of the lungs: they are constantly “overinflated”. The problem with this configuration is that the lung walls have little elasticity and ventilation will require more effort. In addition, the diaphragm has little mobility and is not very effective in participating in the ventilation effort. This situation is thus counterproductive: ventilation initially increases to meet an increase in energy demand, but this same ventilation requires more and more effort, which worsens the total energy expenditure, and finally the organism is unable to meet this expenditure.

Blood stealing

Blood carries O₂ to different systems in the body that use it to produce energy as needed. The term “blood stealing” refers to how different systems can compete for available energy resources. When running, the locomotor system consumes more energy. This energy is supplied by the respiratory and cardiovascular systems. But the latters also need energy. When everything is going well, there is a relative harmony between the systems, allowing the locomotor system to increase in intensity. However, under certain conditions, the distribution of these resources is no longer efficient and will typically penalize the locomotor system and the running performance. This “disharmony” can be caused by different events. For example, during intense effort, the increase in intra-thoracic pressure can negatively affect cardiac performance, and therefore blood will have more difficulty supplying the limbs. In addition, the muscles of ventilation can become increasingly energy intensive if intense effort is maintained. The diaphragm, which consumes 3-5% of total O₂ during moderate effort, will reach a consumption of 10-16%. To this must be added that of the other respiratory muscles. This can cause a relative stealing of blood supplying the limbs of the locomotor system to the respiratory muscles. This phenomenon is called the metaboreflex. Finally, we can point out that the hyperinflation of the lungs described above probably participates in this phenomenon since it imposes an energy overload on the system. This stealing of energy resources penalizes the locomotor system and thus the running experience.

Hyperventilation

As previously explained, physical effort will increase the activity of the respiratory system in order to meet energy requirements. This increase is characterized by an increase in respiratory frequency and amplitude. In the vast majority of cases, the response of the respiratory system is adapted to the demand. But in some cases, the system “goes into overdrive”. In fact, it may be that, in order to provide an adequate volume of air per minute, the respiratory frequency is favored to the detriment of the amplitude. It would seem that women are more prone to this, due in part to a smaller average lung volume. This tends to accelerate breathing, the critical lung capacity being reached more quickly. In addition, running, in comparison to other activities, favors the respiratory frequency relative to the amplitude. This would be due to the fact that the diaphragm must ensure two antagonistic functions between engagement in postural maintenance and mobility for ventilation. But also the rhythmicity of running would tend to impose on the runner a cadence that favors a greater frequency rather than a greater amplitude. Moreover, this seems to be even more marked on slopes (20-30% gradient) where thoracic-lumbar coordination is diminished, affecting ventilation accordingly. However, a too high respiratory rate, when the system gets too excited, can lead to hyperventilation. The latter is characterized by a decrease in the CO₂ content of the blood. By a purely biochemical mechanism, the peripheral tissues are then less supplied with O₂ and fatigue of the locomotor system sets in more quickly⁴. In addition, a low CO₂ content in the blood tends to reach a maximum of respiratory amplitude earlier. This will then be compensated for by increasing frequency, encouraging a vicious cycle. Finally, a high respiratory rate can promote the development of lung hyperinflation, as explained above. In the end, hyperventilation will have a negative impact on running.

Conclusion

In this first part, we have seen that, during running, energy expenditure and locomotion speed increase. The respiratory frequency and volumes adapt in response and allow energy production. Beyond the metabolism, the respiratory chain facilitates locomotion. This adaptation is usually successful. But in some cases, a weakness and/or misuse of the respiratory chain can cause hyperinflation of the lungs, blood stealing and hyperventilation. It is interesting to note that these three problems can be interconnected and can reinforce each other. Breathing is then limiting and this will cause breathlessness. Now that we know the main mechanisms of dysfunctional breathing that can limit running, we can ask ourselves the question: are there any breathing tools that can be put in place so that breathing is not limiting? This is precisely the objective of the second part of this article.

🔥❄️🧠✌️

Sébastien.

¹ I myself am far from mastering sports physiology, as it is not my specialty. The latter concerns much smaller biological entities, bacteria. I rely on my background in general biology and self-taught physiology to provide these blog posts. By the way, I don’t claim to be a running coach either. Just a breathing instructor who comes to put his two cents in, because there’s nothing like a little transdisciplinarity.

² In scholarly terms, one would say that tachypnea precedes hyperpnea to regulate respiratory homeostasis. Useful for scrabble.

³ This involves regulating the rates of inspiration and expiration to maintain a stable respiratory volume.

⁴ When the CO₂ content in the blood decreases, this is called hypocapnia. The amount of CO₂ in the blood determines the pH of the blood. Hypocapnia therefore changes the blood pH by making it more alkaline. The chemical bond between hemoglobin and O₂ in oxyhemoglobin is pH dependent. The more alkaline the pH, the stronger this bond and the more difficult it is to release O₂ to the tissues. This is the Bohr effect.

References:

Harbour, E., Stöggl, T., Schwameder, H., & Finkenzeller, T. (2022). Breath Tools: A Synthesis of Evidence-Based Breathing Strategies to Enhance Human Running. Frontiers in physiology, 13, 813243. https://doi.org/10.3389/fphys.2022.813243

Kandola, A., Ashdown-Franks, G., Hendrikse, J., Sabiston, C. M., & Stubbs, B. (2019). Physical activity and depression: Towards understanding the antidepressant mechanisms of physical activity. Neuroscience and biobehavioral reviews, 107, 525–539. https://doi.org/10.1016/j.neubiorev.2019.09.040

Mok, A., Khaw, K. T., Luben, R., Wareham, N., & Brage, S. (2019). Physical activity trajectories and mortality: population based cohort study. BMJ (Clinical research ed.), 365, l2323. https://doi.org/10.1136/bmj.l2323

Reimers, C. D., Knapp, G., & Reimers, A. K. (2012). Does physical activity increase life expectancy? A review of the literature. Journal of aging research, 2012, 243958. https://doi.org/10.1155/2012/243958