Normal breathing volume during rest is 4 to 6 litres of air per minute. Breathing a volume which is in excess of normal causes a loss of the gas carbon dioxide. This in turn leads to a number of events including the following:

  • The bond between the red blood cells and oxygen becomes more ‘sticky’ leading to reduced delivery of oxygen to tissues and organs
  • Smooth muscle surrounding blood vessels and airways constrict, causing reduced blood circulation and increased breathlessness
  • pH of the blood changes towards alkaline affecting our immune system and more

You may be thinking at this point, “My breathing is fine, so why change it?” In fact, whenever a stranger asks my wife what I do for a living she replies, “He helps people breathe,” to which the reaction is usually laughter or disbelief.

Yes, breathing is natural and involuntary. Luckily, we don’t have to remember to take each breath or we would have ceased living a long time ago. But while breathing is the most natural thing in our lives, many factors of modern life negatively affect our breathing, such as:

  • Stress
  • Sitting at a desk all day
  • Excessive talking
  • Processed foods
  • Stuffy environments
  • The commonly held belief that it’s good to take deep breaths


During a presentation to a group of runners who were due to compete in the Dublin city marathon the following day, I posed the following question: “Who here believes that taking a large breath into the lungs during rest will increase oxygen content of the blood?” Immediately, 95% of the runners raised their arms, and I have found that such a belief is endemic throughout the world of physical exercise. Ironically, it is exactly the wrong thing to do if you want more oxygen and more endurance.

Based on this belief, many athletes adopt the practice of intentionally taking deep breaths during times of rest, during training and especially when the going is hard. However, by doing so, they are in fact limiting improvements to their performance. It is no wonder that regardless of how hard some athletes train, they still find it extremely difficult to improve their fitness levels beyond a certain point. It is also not surprising that many elite athletes experience sickness and poor health soon after they retire.

Carbon Dioxide: Not just a waste gas!

The concentration of carbon dioxide in the atmosphere is very low, and therefore this gas is not carried into the lungs when we breathe. Instead we produce it in the tissue cells during the process of converting food and oxygen into energy. Maintaining a normal breathing volume ensures that the correct amount of carbon dioxide remains in the lungs, blood, tissues and cells. So what are the negative effects of creating an increased sensitivity to carbon dioxide when we over-breathe?

Carbon dioxide performs a number of vital functions in the human body, including:

  • the delivery of oxygen from the blood to the muscles and organs
  • the opening and closing of smooth muscles surrounding the airways and blood vessels
  • the regulation of blood pH


Delivery of oxygen from the blood to the muscles and organs

One of the fundamental elements of the OxyAthlete technique is to understand the so-called Bohr effect – the way in which oxygen is released from red blood cells and delivered to the muscles. This exchange forms the core of unlocking your body’s true potential when it comes to sport and exercise, allowing you to raise your game and achieve the results you really want.

The Bohr effect was discovered in 1904 by the Danish physiologist Christian Bohr (father of Niels Bohr, the Nobel Prize winner physicist—and footballer). In the words of Christian Bohr, “The carbon dioxide pressure of the blood is to be regarded as an important factor in the inner respiratory metabolism. If one uses carbon dioxide in appropriate amounts, the oxygen that was taken up can be used more effectively throughout the body”.2

Over-breathing is detrimental to the release of oxygen from the blood, and in turn affects how well our muscles are able to work. Author of the book “Respiratory Physiology”, John West tells us that “an exercising muscle is hot and generates carbon dioxide, and it benefits from increased unloading of O2 [oxygen] from its capillaries.”3

In simple terms: haemoglobin is a protein found in the blood, and one of its functions is to carry oxygen from the lungs to the tissues and cells. The crucial point to remember is that haemoglobin releases oxygen when in the presence of carbon dioxide. When we over-breathe, too much carbon dioxide is washed from the lungs, blood, tissues and cells. This condition is called hypocapnia and strengthens the bond between oxygen and haemoglobin, resulting in reduced oxygen release and therefore reduced delivery of oxygen to tissues and organs. With less oxygen delivered to the muscles, they cannot work as effectively as we might like them to. The urge to take bigger, deeper breaths when we hit ‘the wall’ during exercise does not provide the muscles with more oxygen but effectively reduces oxygenation.

In contrast, when breathing volume remains nearer to normal levels, the pressure of carbon dioxide in the blood is higher, loosening the bond between haemoglobin and oxygen, meaning that there is a greater delivery of oxygen to the muscles. The better we can fuel our muscles with oxygen during activity, the longer and harder they can work, and the lower lactic acid levels will be.


The Bohr effect can be illustrated using the oxygen disassociation curve above, which plots blood oxygen saturation on the vertical axis against the amount of oxygen in the blood on the horizontal axis. Within the red cells are proteins known as haemoglobin which contain iron. One of the functions of haemoglobin is to carry oxygen from the lungs to the tissues and The Bohr effect can be illustrated using the oxygen disassociation curve above, which plots blood oxygen saturation on the vertical axis against the amount of oxygen in the blood on the horizontal axis. Within the red cells are proteins known as haemoglobin which contain iron. One of the functions of haemoglobin is to carry oxygen from the lungs to the tissues and cells of the body where it is released in order to burn nutrients for the production of energy. Oxyhaemoglobin saturation on the vertical axis refers to the percentage amount of haemoglobin which is occupied with oxygen. The normal saturation of haemoglobin with oxygen is between 95 to 99%, attributable to silent and barely noticeable breathing during rest.

When you breathe more than your body requires, carbon dioxide pressure is reduced, which in turn causes pH to change towards alkaline. This alteration shifts the S-shaped curve on the graph to the left and results in oxygen sticking to haemoglobin. With less oxygen being released, the percentage saturation of oxygen in the blood is higher.

Dilation and constriction of airways and blood vessels

Breathing too much can also cause reduced blood flow. For the vast majority of people, two minutes of heavy breathing is enough to reduce blood circulation throughout the body, including the brain. In general, blood flow to the brain reduces by 2% for every 1mmHg decrease in carbon dioxide.4(a normal level is 40mmHg). A study by Gibbs to assess arterial constriction induced by hyperventilation found that blood vessel diameter reduced in some individuals by as much as 50%.5


Most people will have experienced constriction of blood flow to the brain resulting from a period spent over-breathing. It doesn’t take very long to feel the onset of dizziness and light-headedness from taking a few big breaths in and out, breathing heavily through the mouth. Similarly, many individuals who sleep with their mouths open may find it difficult to get going in the morning. Regardless of the amount of time spent sleeping, they are still tired and groggy for the first few hours after waking. It is well documented that habitual mouth breathing during waking and sleeping hours results in fatigue, poor concentration, reduced productivity and a bad mood.6-12 Hardly an ideal recipe for quality living.

The same can also be true of individuals whose occupations involve considerable talking, such as school teachers or salespeople, who are only too aware of how tired they feel following a day of work. This is not necessarily due to mental or physical stimulation, but is more likely due to the effect of increased breathing during excessive talking. Increased breathing without a proportionate increase in metabolic activity results in a loss of carbon dioxide and reduced blood flow.

Depending on genetic predisposition, the loss of carbon dioxide in the blood can also cause the smooth muscles of the airways to constrict, resulting in wheezing and breathlessness. A study by Dr van den Elshout from the Department of Pulmonary Diseases, University of Nijmegen, The Netherlands explored the effect on airway resistance when there is an increase of carbon dioxide (hypercapnia) or a decrease (hypocapnia).13

Altogether, 15 healthy people and 30 with asthma were involved. The study found that an increase of carbon dioxide resulted in a “significant fall” in airway resistance in both normal and asthmatic subjects. This simply means that the increase of carbon dioxide opened the airways to allow a better oxygen transfer to take place. Interestingly, individuals without asthma also experienced better breathing.13

The feeling of chest tightness, excessive breathlessness and the inability to take a satisfying breath is experienced by many athletes, including those without a prior history of asthma. Later on in this book, I will further explore the relationship between breathing volume and exercise-induced narrowing of the airways, and, more importantly, I will provide you with the tools to help prevent asthma symptoms. This is an area of considerable importance to me, having spent years gasping for breath from even the slightest of exercise. Little did I know that my continuous mouth breathing and gulping of air into my lungs was in fact worsening my asthma. For the past twelve years, I have helped thousands of children and adults get to the root of their asthma, providing them with lifelong tools to keep it to a minimum. For those who suffer from asthma or have relatives or friends with asthma, they can find a whole program to end asthma without drugs at my website:

The regulation of blood pH

pH Co2 Link

The scientific evidence clearly points to the fact that carbon dioxide is an essential element in regulating our breathing, optimising blood flow and releasing oxygen to the muscles, and maintaining correct pH levels – all of which are essential for improving sporting performance, endurance and strength. We have also seen how over-breathing can negatively affect the amount of CO2, which can in turn limit our ability to exercise effectively and, in some cases, lead to health issues and injury. Knowing how your respiratory system works, and the important role carbon dioxide plays in its efficiency, allows you to maximise your potential when exercising.

Case study: 37 year old competitive cyclist

Eamon is 37 years old and has been an avid cyclist since his late teens. His usual training regime amounts to two 150km cycles per week. Despite his years of regular training, Eamon came to me because he was experiencing excessive breathlessness and a desperate need for air even while cycling at a moderate pace. He also complained of temporary blackouts during a 150 km cycle. He had visited his doctor and a consultant, who both ruled out asthma. When I met Eamon, he showed signs of habitual mouth breathing which culminated in excessive breathing movements from the upper chest.

Following two weeks of the OxyAthlete program, Eamon’s breathlessness was markedly reduced and he experienced no more blackouts. In this case, the cause of his breathlessness and blackouts was chronic hyperventilation. Eamon’s irregular and over-laboured breathing during resting periods translated into heavy breathing during exercise. His over-breathing during cycling caused an excessive loss of carbon dioxide, which resulted in a reduction of blood flow to the brain and the temporary blackouts. Of course, not everyone with reduced carbon dioxide experiences blackouts, as the effect will depend on genetic predisposition, but in all cases there will be some negative symptom to be found. As the late Cardiologist Claude Lum explains: “Hyperventilation presents a collection of bizarre and often apparently unrelated symptoms, which may affect any part of the body, and any organ or any system.”15

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