Have you ever watched a sleeping baby breathe? Or a dog soaking in the sun breathe? Notice that their bellies, rather than their chests, rises when they inhale and becomes flat when they exhale. This is called diaphragmatic breathing (or also called ‘belly breathing’). The diaphragm is a dome-shaped muscle at the base of the lungs, between the chest and the abdomen. When you inhale (breathe in),  the diaphragm contracts and moves downwards, stretching your lungs elastically to expand and fill your chest; that creates a vacuum and air flows in. When you exhale (breathe out), the diaphragm relaxes and moves upwards, allowing the lungs to elastically recoil to their deflated position; this squeezes out the air out of your lungs.


Under the everyday life stressors (i.e., tight clothing, sedentary lifestyle, talking a lot, stress, inefficient ergonomics, etc.) many of us unintentionally stop using this innate ability to correctly engage the diaphragm while breathing and we shift to a shallower type of breathing (‘chest breathing’). Chest breathing depends more on the accessory muscles of breathing like the intercostals (the muscles lining the ribcage).

Breathing is an automatic process, controlled by the autonomic nervous system (or ANS). The ANS is a division of the nervous system that unconsciously regulates many of the automatic bodily functions that we depend on every second such as our heart rate, digestion or blood circulation to different organs. 

In a recent literature review, it was found that there is evidence to suggest that concussion does impact the function of the autonomic nervous system (Pertab et al., 2018). The nature of the symptoms from autonomic dysfunction confound with those of post-concussion syndrome.

In the study of the relationship between mTBI and the autonomic system, various modalities have been used.
Among the available noninvasive techniques for assessing the autonomic status, measuring heart rate variability (HRV) has been commonly used (Esterov et al., 2017).
Diaphragmatic breathing is required to effectively train one’s HRV.
HRV is frequently impacted in individuals with concussion or mild traumatic brain injury (Thompson et al., 2012).
Moreover, post-concussion syndrome consists of many symptoms (e.g., cognitive dysfunction, emotional regulation, headaches, etc.) for which HRV has evidence as a useful treatment. An added bonus is that there are relatively no side effects to HRV training and concussion patients are generally more sensitive to the side effects of medications; and the medications are often less effective than in the non-concussion population (Ashina et al., 2020).
In concussion, some of the adversely affected networks in the brain may participate in the affective network (i.e., anterior cingulate, amygdala, anterior insula, etc.). This is a network of brain structures that are involved in emotional regulation. It is not just involved in the demonstration of emotions, but also memory, pain tolerance and many other functions.
This is intuitive, consider the following examples:
1. A young child really wants earrings and is willing to endure the pain for the same, but when her little sister lightly hits her, she cries.
2. When you are really interested in something, you tend to absorb more of the material.
This affect network is connected to important structures in the brainstem like the locus coeruleus in the pons and the nucleus of the solitary tract (NST) in the medulla. The NST, for example, influences activity in many brain regions like the locus coeruleus, cingulate, amygdala and the hypothalamus that, in turn, influence our sympathetic nervous system’s activity, our blood pressure and heart rate, fear behaviours, and the hormone-pituitary-adrenal (HPA) axis (Thompson et al., 2015).
HRV breathing stimulates vagus afferent feedback to the brain stem.
This may theoretically explain why HRV has grade A evidence for the treatment of migraine. As migraine is a condition of cortical hyperexcitability that involves the brainstem. Inhibiting this excited signal in the brainstem before it goes up to the trigeminal nerve and the cortex with this vagus afferent feedback (from HRV training) may be how HRV works. When one considers that many conditions of cortical hyperexcitability (e.g., tension-type headache [TTH], migraine-like headache, dizziness, anxiety/depression, PTSD, chronic fatigue syndrome, temporomandibular disorder [TMD], myofascial pain syndrome [e.g., chronic neck pain], chronic pain syndromes) exist in the context of post-concussion syndrome, it is understandable why so many have started studying HRV training and its effects in post-concussion syndrome patients.

Proper breathing contributes to maintaining the acid-base homeostasis of the blood. Overbreathing (or ‘over-ventilating’) is a common type of breathing dysregulation that happens when people breathe out too much carbon dioxide (CO2). Many people think about the importance of having enough oxygen (O2), and that  CO2 is “just waste”. However, we need enough CO2 to maintain proper acid-base chemistry in the blood so our cells and enzymes can work optimally. Breathing out too much CO2 disrupts that homeostasis resulting in physiological, emotional and/or cognitive symptoms like:

  • shortness of breath
  • heart palpitations
  • elevated heart rate
  • numbness and tingling in the hands or feet
  • shakiness
  • dizziness
  • feelings of unreality
  • muscle tension
  • fatigue
  • headache
  • nausea
  • difficulty concentrating
  • “foggy” mind
  • diaphoresis (sweating) and shivering
  • blurred vision
  • dry mouth

In moderate overbreathers there is a 30-40% reduction of O2 to the brain and in severe overbreathers this amount can go up to a 60% reduction of O2 to the brain (Khazan, 2013). If overbreathing persists chronically it can lead to or worsen chronic fatigue, asthma, COPD, functional abdominal pain, fibromyalgia, hypertension, chronic muscle pain and lower back pain, depression, PTSD, anxiety disorders, psychological stress/irritability, insomnia, migraines, tension-type headaches, TMJ pain and autonomic dysfunction to name a few. (Khazan, 2013).

While one can still over-breathe with any breathing style, it is more commonly present in those that practice quicker, shallower breathing – more typical of chest breathing. Using mindfulness techniques, patients can often intuitively feel the diaphragmatic breathing form that feels natural for them; the use of biofeedback expedites the learning curve.

Some patients need feedback regarding how much CO2 they are blowing off so that they can adjust their breathing to restore more physiologically-sound blood chemistry; fortunately, most will not need to use this expensive equipment.

Other than the benefits listed above about regulating CO2 levels to promote ideal blood pH and ionic potentials, diaphragmatic breathing improves O2 perfusion to the organs which in turns can also help with performance and athleticism (Hunt et. al., 2018).

Regulating CO2 levels can help alleviate some concussion symptoms. Training diaphragmatic breathing also decreases musculoskeletal tension, particularly around the neck, as it requires less effort and energy to breathe, and through efficient core recruitment, can improve balance.

There is evidence suggesting it may even help patients suffering from asthma (Venkatesan et al., 2012).

In a review of heart rate variability (i.e., trained by using diaphragmatic breathing) and concussion, biofeedback-based training of heart rate variability was found to be an effective intervention after concussion, and that this would then likely have a positive impact on cognitive performance (Conder et al., 2014).
Research has shown promising effects from using biofeedback to train HRV reflected in positively impacted mood and emotion regulation, post-concussion symptoms, and decreased headache severity (Lagos et al., 2013; Kim et al., 2013).

At the Toronto Concussion Clinic, one area where we start rehabilitation is by teaching our patients diaphragmatic breathing. We call it low-and-slow diaphragmatic breathing (LSDB) so as to avoid giving the impression that there is striving or effort involved; it is an easy, natural way of breathing. If we are not diaphragmatically breathing now, rest assure, we once did. As patients reconnect with this natural form of breathing, they start noticing how much easier it is, and they wonder why and how they ever got out of habit of doing it. We then train these patients in HRV training. In fact, as people recover and reintegrate into the activities of their pre-concussion lives, they comment that one of the most helpful skills they learned is HRV training.

To train this, we combine biofeedback training with mindfulness.

  • First, find a comfortable, quiet space to lie down.
  • Can you recognize if there is any tension in your shoulders, neck, chest or core? Consciously minimize that tension.
  • Place one hand on your upper chest and one hand on your abdomen (belly) to identify where the motion is coming from. And breathe in.
  • Allow the motion to shift to your abdomen while minimizing the motion that takes place from the chest. The hand on your chest should remain still while the one on your abdomen should rise.
  • If helpful, you can use visualization strategies like imagining a balloon expanding, or imagining air flowing past your lungs and into your belly to guide your breath.
  1. Ashina H, Iljazi A, Al-Khazali HM, et al. Persistent post-traumatic headache attributed to mild traumatic brain injury: Deep phenotyping and treatment patterns. Cephalalgia. 2020;0(0):1-11. doi:10.1177/0333102420909865
  2. Conder, R. L., & Conder, A. A. (2014). Heart rate variability interventions for concussion and rehabilitation. Frontiers in Psychology, 5, 890. http://doi.org/10.3389/fpsyg.2014.00890.
  3. Esterov D, Greenwald BD. Autonomic dysfunction after mild traumatic brain injury. Brain Sci. 2017;7(8):1-8. doi:10.3390/brainsci7080100.
  4. Hunt, Melissa & Rushton, James & Shenberger, Elyse & Murayama, Sarah. (2018). Positive Effects of Diaphragmatic Breathing on Physiological Stress Reactivity in Varsity Athletes. Journal of Clinical Sport Psychology. 12. 1-12. 10.1123/jcsp.2016-0041.
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  7. Lagos, L., Thompson, J., & Vaschillo, E. (2013). A preliminary study: Heart rate variability biofeedback for treatment of postconcussion syndrome. Biofeedback, 41(3), 136-143. https://doi.org/10.5298/1081-5937-41.3.02.
  8. Pertab, J. L., Merkley, T. L., Cramond, A. J., Cramond, K., Paxton, H., & Wu, T. (2018). Concussion and the autonomic nervous system: An introduction to the field and the results of a systematic review. Neurorehabilitation, 42(4), 397–427. http://doi.org/10.3233/NRE-172298.
  9. Thompson J., Hagedorn D. (2012). Multimodal analysis: new approaches to the concussion conundrum. Journal of Clinical Sport Psychology, 6, 22–46. doi:10.1123/jcsp.6.1.22.
  10. Thompson, Michael; Thompson, Lynda. Functional Neuroanatomy. The Association for Applied Psychophysiology and Biofeedback 2015.
  11. Venkatesan, Prem & Sahoo, Ramesh & Adhikari, Prabha. (2012). Effect of diaphragmatic breathing exercise on quality of life in subjects with asthma: A systematic review. Physiotherapy theory and practice. 29. 10.3109/09593985.2012.731626.

Last updated: May 2020