22 Nov 2018 - The Importance of Nasal Breathing, Pt. 2

So, how can you tell if you have a problem with carbon dioxide tolerance? Read on to learn more and find out how you can test yourself!

In Part 1 (which you can find here) we discussed why the nose is so important in breathing and what the benefits are to nasal breathing.

In order to understand the relationship between oxygen and carbon dioxide, we need to understand the Bohr Effect, which describes how the pH of the blood impacts the affinity of oxygen to haemoglobin.

Let’s do a quick biology recap of what happens when we inhale:

Step 1: Air enters the lungs

Step 2: Oxygen passes into the blood stream via the alveoli

Step 3: Oxygen binds to haemoglobin (red blood cells) and is transported around the body

Step 4: Oxygen is released from haemoglobin where it is required at the cells

Back to the Bohr Effect…

When the pH of the blood drops (it becomes more acidic), oxygen is more readily released by haemoglobin (so our cells can use it). Conversely, as the pH rises (becomes more alkaline), haemoglobin will hold onto oxygen (so our cells cannot use it). Carbon dioxide is one such gas that makes the blood more acidic. The key point to take away here is that the more carbon dioxide there is in the blood, the more readily oxygen is released from haemoglobin for our cells to use.

The rate and volume of breathing is determined by receptors in the brain that are sensitive to levels of carbon dioxide, oxygen and blood pH level. When carbon dioxide rises and blood pH falls, we are stimulated to increase our rate of respiration to expel the carbon dioxide. Crucially, some carbon dioxide is retained in the body and correct breathing patterns rely on this.

Those who over-breathe (mouth breathers) have a habit of breathing more air than is required and importantly, too much carbon dioxide is expelled. When this habit lasts for weeks, months or years, it results in the body having chronically lowered levels of carbon dioxide. Due to this, the receptors in our brains develop an increased sensitivity to lower levels of carbon dioxide.

With this lowered limit of Carbon dioxide tolerance we are more regularly stimulated to increases in breathing rates (even though it is not required), and this is where it's impact on performance comes into focus.

Carbon dioxide is a by-product of metabolism; as our activity levels increase, so does the production of carbon dioxide. if we have a lower sensitivity to this, it means that lower levels of intensity will cause us to breathe heavily, pant, or struggle to breathe and ultimately "gas out" much earlier than we should.

You may be thinking that breathing more heavily gets us more oxygen, but this is not quite the case. Blood oxygen saturation is the percentage of oxygen-saturated haemoglobin relative to total haemoglobin in the blood. In normal folks, it sits between 95-99%. This normally stays the same at rest or at exercise - it is very carefully regulated. What this means is that even under increasing levels of intensity our blood does not carry more oxygen.

However if we have decreased sensitivity to carbon Dioxide (because we mouth breathe), haemoglobin has a harder time releasing oxygen for us to use.

To truly develop our aerobic system’s efficiency, we need to increase our tolerance to carbon dioxide and use breathing mechanics appropriate for the level of intensity. Unfortunately, just going HAM on any given workout is not going to fit the bill in these cases!

Whilst we will discuss breathing mechanics during exercise more in our next blog post, it is worth noting that breathing through the mouth is appropriate at certain times, but to be able to control our use of our energy systems, we need to learn to control our breathing.

So, how can you tell if you have a problem with carbon dioxide tolerance? You can perform the following test below, all you need is yourself and a stop watch…

Find a comfortable sitting position

Take 3 normal breaths in and out through the nose

After the 4th inhale (through the nose), start the timer and begin to exhale (again through the nose) as slowly as you can.

When you stop exhaling or need to take a breath in, stop the timer

Post your times to the comments section, and in the next blog post I will reveal what your score tells you about your carbon dioxide tolerance!


A) Gymnastics Tests

A1) L-Sit (or L-Tuck) hold: For max time

A2) Forearm plank hold: For max time

B) Conditioning
3 rounds for time:
25 Toes to bar (or Ab-mat sit-ups)
50 ft Double kettlebell overhead carry
50 ft Double kettlebell overhead walking lunge