Your BOLT score is an indicator for your CO2 tolerance. Your CO2 tolerance is important to your fitness, because it affects how efficiently your body is able transport oxygen to your muscles and all your body cells. But let's start at the beginning:
It's all about CO2!
Carbon dioxide, or CO2, is responsible for the fact, that we rarely forget to breathe. Hold your breath right now, wait and feel the signs of your body…
Usually we first notice a slight pressure in our throat or upper chest area. This is caused by the rising CO2 level, which expands our blood vessels. In addition, receptors that measure the CO2 pressure, via the respiratory centre in the brain, incite our breathing muscles to start working. If, other than just now, we do not pay attention, we do not even notice the pressure and breathe in automatically. And we do this independently of our oxygen reserves in the body and looong before these could become dangerously scarce.
How is CO2 produced in our body?
CO2 is a consequence of our bodies energy production. As a fire, that needs oxygen to burn and emits CO2 into the air, our cells use oxygen to produce energy and for their functioning. The cells receive the oxygen by inhalation via lungs and blood and exchange it for CO2, which in turn leaves the body via blood and lungs in the air we exhale. This also explains, why we breathe faster during sports: not primarily because our body needs more oxygen, but because our muscles produce more CO2, which it wants to get rid of.
The Bohr effect
CO2 thus, is responsible for our respiratory stimulus and therefore anything but a waste product. But what does our breathing stimulus have to do with our fitness? It's all about the Bohr effect. Mr. Bohr (1855-1911) found out, that the higher the CO2 level in the blood, the easier oxygen is transferred from the blood into the cells. But the faster we breathe, the less time the body has to accumulate CO2, before it leaves the body with the exhalation. An averagely high respiratory rate therefore results in an averagely low CO2 level in the blood. This means, that if we tend to breathe too quickly and a too big volume of air, the oxygen we inhale cannot be optimally transported into our cells, due to the lack of CO2 in the blood. At the same time, our body gets used to a low CO2 level over time and our CO2 tolerance is ruined. Our breathing stimulus sets in more quickly than necessary for optimal oxygen transfer and we get stuck in a kind of "high ventilation cycle".
If you like to know where you stand in this respect, have a look on your breathing rate. Count your breaths per minute. At rest, it should be no more than about ten breaths per minute - optimally about six to eight times. If your number is more than 12 - 15 times per minute at rest, you definitely have potential :).
How to measure your BOLT score
Measuring our own breathing rate by counting breaths, is not so easy. As soon as we concentrate on our breath, we no longer know, how we would be breathing normally. That's why you may prefer to measure your BOLT score. It is a proven measure of our CO2 tolerance. BOLT stands for Body Oxygen Level Test. The BOLT score indicates how many seconds it takes for our body to give the signal to breathe in, after exhaling.
This is how you measure your BOLT score:
Lie down and breathe consciously until you feel relaxed and your breathing flows smoothly.
Take a normal breath in and breathe out normally and hold your breath
Stop the time from the moment you stop breathing until the moment your body gives you a clear sign to breathe in.
Our CO2 tolerance is optimal when our BOLT score is around 40 seconds. However, since most of us show a latently increased stress level, the BOLT score for most "healthy" people is around 20 seconds. For people with respiratory problems, it can also be 10 and below.
When you measure your BOLT score for the first time, you are probably not sure, whether you have read your body's signs correctly and, if the score is correct. Make sure, you DO NOT measure how long you can hold your breath, but stop the watch at the first clear sign of your body. This can be a strong urge to breathe, the urge to swallow or a twitching of the diaphragm below the lungs. And if you stop in time, your subsequent inhale is not bigger, than a normal one. However, a few seconds more or less is not important. Just always refer to the same signs, in order to observe your personal progress. You will also notice a difference, whether you measure while sitting or lying and depending on your mental or physical condition. A good way to measure BOLT, is in the morning, just before getting up from bed. If you have measured your BOLT for a few days in a row in the same way, you will be able to categorize your CO2 tolerance, based on the above numbers. If your BOLT score is not particularly high, you can take it easy. You have probably lived quite well up to now and your BOLT score will not change this fact. It might also feel good to know, that many athletes have relatively low BOLT scores. Training plans often neglect breathing and athletes simply do not use their full potential. Athlete or not, isn’t it great to know, that we’ve got potential!? Especially, if you feel like doing something for your health or improving your performance.
How to improve your BOLT score
When I started myself to take care of my CO2 tolerance, my BOLT score was around 15 seconds! I had been a Wim Hof instructor for a while and had started to wonder, why my ability to hold my breath during Wim Hof breathing was slowly decreasing over time (see also Blog “Help, my breath holds are getting shorter”). As a hobby apnoea diver, where my performance directly depends on my CO2 tolerance, I was anything but amused. When I started to do more research about breathing physiology, I soon realized: I was breathing too much. Not so much because of the Wim Hof method, it simply was the straw that broke the camel’s back. Much more, I had never had a close look at my breathing pattern in everyday life and during (overwater) sports.
Stay tuned!
The good news: a few weeks to a few months are enough to increase a BOLT score to a high level. Mine had risen from 15 to around 40 seconds within about six weeks. And if I can do it, so do you! Start right now with nasal breathing, in everyday life and in sports. For more information and simple and effective exercises, try the Oxygen Advantage Method or Breatheology. Remember: Breathing is a basic need. Restricting ourselves can feel stressful at first. Therefore, approach all exercises in a relaxed manner and take your time. Usually we overestimate what we can achieve in a short time and underestimate what is possible in the long run. Stay tuned, it’s worth it!
Links & Literature
Oxygen Advantage official Webseite, click on STORE to find online Trainings and products, which support healthy breathing.
Upcoming workshops with Helena , jala coaching
Book Oxygen Advantage. Simple, Scientifically Proven Breathing Techniques to Help You Become Healthier, Slimmer, Faster, and Fitter. Patrick McKeown, 2019
Book Breathing for Yoga. Applying the Science behind ancient Wisdom in a modern World. Patrick McKeown & Anastasis Tsanis, 2023
Book Breath. The New Science of a lost Art. James Nestor, 2021