This is the first of four pieces in the series Breathing, Revisited. The series returns to breathing from the side of the research, eight years into offering Rolfing sessions. It stands in a different place from the four-part breathing series written back in 2015, during basic training. This first piece takes up the quantity of breath itself.
Which is harder, breathing in or breathing out?
When I begin a first session, I ask:”When you breathe, which is harder — breathing in, or breathing out?”
Then I direct attention to the shoulders, the front and back of the chest, the sides of the ribcage, and ask:”Which muscles are you breathing with?”
Clients notice that they have been recruiting far more muscles into breathing than they thought.
And there is something further:A great many people are breathing too much.
This is not widely known.
Breathing too much — it starts with the mouth
Just as there is a right amount of water and food to take in over a day, there is an ideal amount of breath. Overeating is bad for the body, and so is overbreathing.
How do you tell whether you are breathing too much? For example:
- Mouth breathing, whether during the day or while asleep
- Snoring, or breathing that stops during sleep
- Visible breathing movement, with the chest moving more than the belly, at rest
- Frequent sighing — occasional is fine, frequent suggests chronic overbreathing
- Hearing your own breath at rest
- Nasal congestion, fatigue, unsteadiness, dizziness — symptoms that overbreathing can produce
If several of these apply, overbreathing is likely.
The Bohr effect — what was found in one laboratory
We take in oxygen and release carbon dioxide roughly 25,000 times a day. The body needs oxygen, but more is not simply better.
Hemoglobin carries oxygen in the blood. How tightly hemoglobin holds onto that oxygen shifts with the acidity of the blood and the concentration of carbon dioxide. When carbon dioxide rises, the grip loosens and oxygen passes more readily into the tissues. When it falls, the grip tightens and oxygen passes less readily.
This is named after the man who found it: the Bohr effect.
In 1904, Christian Bohr of the University of Copenhagen published it together with two of his students, Karl Hasselbalch and August Krogh. Using an instrument Krogh had devised, they measured the full oxygen equilibrium curve in whole blood for the first time. They had set out to confirm the accepted view of the day, but what they measured did not have the accepted shape — it traced an S. And from the same experiment, they saw that the affinity for oxygen moves inversely with the pressure of carbon dioxide.
Their paper pointed out that in the capillaries of the lungs, carbon dioxide is lost and the uptake of oxygen is favoured; in the peripheral capillaries, carbon dioxide is added and the release of oxygen is favoured.
Of the three, Krogh received the Nobel Prize in Physiology or Medicine sixteen years later. And Christian Bohr’s son was Niels Bohr, of the atomic model.
How much does it actually do?
What I find interesting is how much the size of this effect depends on the conditions.
Across the ordinary arteriovenous range, blocking the Bohr effect reduces oxygen unloading by about 8 percent. One estimate of what the Bohr effect alone contributes to oxygen release in humans puts it at 1.3 percent.
Push the conditions, though, and the picture changes. Blood at a carbon dioxide pressure of 40 mmHg gives up 69 percent of its oxygen as the oxygen pressure falls from 100 to 20. Blood at a carbon dioxide pressure of only 5 mmHg gives up 2.3 times less under the same conditions. In a calculation where the Bohr effect is removed altogether, the amount of oxygen released drops twenty-two-fold.
So: small within the everyday range, and suddenly large toward the extremes.
There is one more thing, less often mentioned. The Bohr effect matters considerably more for carrying carbon dioxide than for carrying oxygen. Under the same block, oxygen unloading falls by 8 percent while carbon dioxide loading falls by 47 percent. It reads more accurately as a mechanism for transporting carbon dioxide that also, along the way, adjusts how oxygen is passes across.
Worth holding onto: the Bohr effect is not a switch that determines whether oxygen is released. It adjusts how readily. What determines the unloading itself is the oxygen pressure gradient between blood and tissue.
What happens when you breathe too much
So what follows from breathing more than you need?
Carbon dioxide is released in excess and its concentration in the blood falls. Going by the direction of the Bohr effect, hemoglobin holds its oxygen more tightly. But that alone does not account for fatigue or dizziness. As the numbers show, the effect within the ordinary range is small.
There is a second line running through this.
The blood vessels of the brain are highly sensitive to changes in carbon dioxide pressure. When hyperventilation lowers arterial carbon dioxide, the pH around the resistance vessels of the brain shifts and those vessels constrict. Blood flow to the brain itself is reduced.
And here the effect is large. For every 1 torr drop in carbon dioxide pressure, cerebral blood flow falls by roughly 2 percent.
Clinically, this mechanism gets used in reverse. When intracranial pressure rises after a traumatic brain injury, deliberate hyperventilation lowers carbon dioxide, constricts the cerebral arterioles, reduces cerebral blood flow and blood volume, and brings the pressure down. Breathing more, in other words, works as a method for reducing blood flow to the brain.
In studies of patients with orthostatic intolerance, hyperventilation slowed cerebral blood flow velocity and worsened symptoms, and rebreathing carbon dioxide improved both within two minutes.
Unsteadiness, dizziness, fatigue. Before oxygen fails to reach the tissues, what happens is that less blood reaches the brain.
Carbon dioxide and the acidity of the blood
Carbon dioxide has another role: regulating the acidity of the blood.
Blood pH is held within a narrow band, between 7.35 and 7.45. That balance is maintained by the lungs and the kidneys. If the blood turns alkaline, the body moves toward retaining carbon dioxide — breathing less. If it turns acidic, toward expelling carbon dioxide — breathing more.
So what turns the blood acidic?
In The Oxygen Advantage, Patrick McKeown writes that eating processed, acid-forming foods turns the blood acidic and that heavier breathing follows. Diet, on his account, is one reason modern people breathe too much.
Here the ground is less firm than it looks.
That blood pH is held within a narrow band by the lungs and the kidneys is established physiology. That diet moves that band is a thinner claim. In a randomised controlled trial using an acidic diet, systemic pH shifted by 0.014 units, while urinary pH — the larger movement by far — shifted by 1.02 units. In healthy people, diet does not move blood pH by any meaningful margin.
McKeown does not state this part flatly either. He leaves it open as a question: whether processed acidic foods bring on poor breathing habits, or poor breathing habits bring on cravings for processed acidic foods.
The main subject here — that we breathe too much — does not fall apart at this point. What falls away is one line of reasoning that traced the cause to diet.
Breathing in through the nose
The simplest way out of overbreathing is to shift from the mouth to the nose. That alone prevents a good deal of it.
James Nestor’s Breath: The New Science of a Lost Art describes an interesting experiment.
Nestor had been troubled by pneumonia and bronchitis, and a doctor suggested he take a breathing class. He then ran an experiment on himself, plugging both nostrils with silicone. Under the supervision of a nasal researcher at Stanford, he lived for ten days breathing only through his mouth, and for the ten days after that, only through his nose.
What happened was striking. Snoring went from a few seconds a night to four hours. Apnea appeared, along with excess stress, disturbed autonomic function, and lost sleep. Over the period after he returned to nasal breathing, these reversed.
Mouth breathing carries a range of costs, which is why breathing through the nose matters so much.
Breathing in a Rolfing session
In Rolfing, the first session is built so that you can feel, through the session itself, what breathing actually is.
Because the work centres on the muscles that do not fatigue, you become able to attend to your breath without the body tiring.
And the diaphragm begins to move, so the organs — which need that movement for health — can move as well. Once the organs are moving, many people find they have arrived at a sense of being ready to use their body awareness.
Conclusion
This piece has shared some of what I have gathered about mouth breathing, nasal breathing, and breathing too much.
What happens when you breathe more than you need? Carbon dioxide falls, and hemoglobin holds its oxygen more tightly. And the vessels carrying blood to the brain narrow. The first is smaller than you would expect; the second, larger. Between what was measured in Copenhagen in 1904 and what is understood now, that is the span.
Note, September 2026
I wrote this piece in April 2023, coming at the subject of overbreathing through Patrick McKeown’s The Oxygen Advantage and James Nestor’s Breath. Both books say the same thing: look at carbon dioxide, not oxygen.
I had received that same idea once before, eight years earlier.
In November 2015, on the second day of a pranayama course taught by Motoko Saito, I was taught the following about breathing. When the concentration of carbon dioxide in the blood rises, the respiratory centre is stimulated and the rate of breathing increases. Pranayama attends to carbon dioxide rather than oxygen, and understanding that point matters.
There was a further step to it. Tension in the body arising from emotion or stress acts on the respiratory centre through the nerves, and breathing becomes fast and shallow. That change in turn raises muscular tension, and the sympathetic nervous system takes over. Practising pranayama accustoms the body to breathing slowly and deeply while carbon dioxide in the blood is high. The point of the training is to be able to arrive at a parasympathetic, resting state even at high concentrations of carbon dioxide.
What this piece covered was what happens when carbon dioxide runs short — and no further. The other side of it, how to be in the body when there is enough, is not here. That was the part I had been told about eight years earlier.
My notes from the time also record what was said in the course about the ujjayi breath. Narrowing the airway by drawing in the throat makes it possible to exhale over a long stretch without unnecessary effort. And drawing in the throat fixes the neck, so that other parts — the collarbones, the ribs — are recruited, and the muscles that ought to work do the working. In the direction of reducing the volume of breath, it points at the same place this piece does.
Less a case of separate sources arriving at the same spot, and more a case of receiving something once and then receiving it again through a different door. In 2023, I had not noticed the overlap.