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VO₂ max is often described as the gold standard measure of aerobic capacity. It represents the maximum amount of oxygen your body can take in, transport, and use during exercise. For athletes it has long been seen as a marker of endurance potential. For the general population it is one of the strongest predictors of long-term health and resilience.
But the way VO₂ max is measured, and more importantly the way it is trained, is often misunderstood. Athletes chase the number on a lab test without really understanding what it means, while many non-athletes assume it is something only professionals need to worry about. The truth is VO₂ max tells us how efficiently your body uses oxygen, how well your cardiovascular system is functioning, and how prepared you are to perform under stress.
In this blog we will look at carbon monoxide rebreathing, one of the scientific methods used to assess VO₂ max, why it matters, and how structured breathing training can increase your own VO₂ max by up to 20%. As one of the leading breathwork coaches in the UK, working with clients across Europe, the USA, and India, I see the same pattern: people chasing numbers in the lab but overlooking the power of consistent breathing training.
In simple terms, VO₂ max is the maximum rate at which your body can use oxygen during exercise. Oxygen is the fuel your muscles need to work. The more oxygen you can deliver and use, the harder and longer you can perform before fatigue sets in.
For athletes a higher VO₂ max is linked to greater endurance and the ability to sustain high workloads. For the general population a higher VO₂ max is strongly associated with reduced risk of cardiovascular disease, better metabolic health, and longer lifespan.
It is important to remember though that VO₂ max is not the only factor in performance. Two people can record the same VO₂ max in the lab but perform very differently on the field or track. This is because how you breathe, how you tolerate carbon dioxide, and how efficiently oxygen is delivered into working muscles also matter.
The standard way to measure VO₂ max is in a lab using a treadmill or bike test while wearing a mask connected to a gas analyser. The workload is increased step by step until exhaustion while oxygen intake and carbon dioxide output are measured. This approach gives an estimate of aerobic capacity and is widely used in sports science.
But there are other ways to measure VO₂ max, and one of the most interesting is carbon monoxide rebreathing.
The carbon monoxide (CO) rebreathing method sounds alarming at first, but in controlled scientific settings it is completely safe. The principle is simple: carbon monoxide binds to haemoglobin in red blood cells much more readily than oxygen. By introducing a very small, safe amount of CO into the lungs and then measuring how much haemoglobin it binds to, scientists can calculate the total haemoglobin mass in the blood.
This matters because haemoglobin is the protein that carries oxygen. The more haemoglobin you have, the greater your potential to transport oxygen to your muscles and tissues. This makes total haemoglobin mass a strong determinant of endurance performance.
Carbon monoxide rebreathing therefore gives researchers a direct way of assessing the oxygen-carrying capacity of the blood, which adds an important layer to the picture provided by treadmill or cycling tests.
By looking at haemoglobin mass rather than just oxygen uptake, scientists gain a clearer picture of performance potential. Two athletes may have the same VO₂ max score, but different haemoglobin levels, which could affect recovery, altitude tolerance, and the ability to sustain repeated efforts.
The limitation is that CO rebreathing is a specialist test requiring equipment and medical oversight. It is not widely used outside research settings or elite sports programmes. But the insight is valuable because it reminds us of a critical truth: performance is not only about how much oxygen you breathe in. It is about how efficiently you transport and use that oxygen.
This is where breathing training becomes so powerful. VO₂ max is influenced not only by your heart and lungs but also by how you breathe every day, how you manage carbon dioxide, and how effectively oxygen is released into tissues.
The Bohr effect is the physiological principle that explains how higher levels of carbon dioxide in the blood allow oxygen to be released more easily from haemoglobin into working muscles. If you chronically over-breathe and blow off too much CO₂, your ability to use oxygen is reduced — even if your VO₂ max looks good in a lab test.
By training CO₂ tolerance through specific breathing exercises you improve oxygen delivery at the muscle level. By improving breathing mechanics you expand lung volume, ribcage mobility, and diaphragmatic function, which all support better oxygen uptake. By learning to regulate your nervous system you can sustain performance under pressure and recover more quickly afterwards.
The carbon monoxide rebreathing method is fascinating science, but here is the important point: you do not need access to specialist equipment or lab tests to improve your VO₂ max. The biggest gains come from how consistently you train your breathing within the exercise you already do.
Our breathwork programs are designed with that in mind. You do not need to add endless new sessions or invest in complicated technology. Instead, by improving the way you breathe — your tolerance to carbon dioxide, your breathing mechanics, your sleep quality, and your ability to stay calm under pressure — you make every training session more effective.
If you follow the programming exactly as set out, you can increase your VO₂ max by up to 20%. That means more speed, more endurance, and more resilience for athletes, and more energy, better recovery, and long-term health for professionals and everyday individuals.
If you want to explore how this can work for you, we offer a free 15-minute consultation. It is a simple way to ask questions, share your goals, and understand how we can help. You can book directly through the blue button floating on this page.
It is easy to think of VO₂ max as a number that only professional athletes should worry about, but the evidence shows otherwise. A higher VO₂ max is strongly associated with reduced risk of disease and longer lifespan. Some researchers even describe it as the single best predictor of long-term health.
This is why training your breathing should not just be reserved for athletes chasing marginal gains. Learning how to breathe efficiently improves oxygen delivery, energy levels, sleep quality, stress resilience, and overall wellbeing. Whether you are preparing for a marathon, managing stress at work, or simply wanting to feel healthier every day, VO₂ max and oxygen efficiency matter to you.
If you want to understand more about our programs and how they are structured, you can read our full Programs Insight.
What is VO₂ max in simple terms?
It is the maximum amount of oxygen your body can use during exercise. Higher VO₂ max means better endurance and health.
Is carbon monoxide rebreathing safe?
Yes, when used in controlled scientific settings. It involves a very small, safe dose and is overseen by medical professionals.
Do I need CO rebreathing or a lab test to improve my VO₂ max?
No. The science is useful for understanding performance, but the improvements come from consistent breathing training, which can be built into your current exercise routine.
How much can breathwork improve VO₂ max?
With consistent, structured practice, you can improve your VO₂ max by up to 20%.
Why is CO₂ tolerance important for performance?
Higher CO₂ tolerance improves oxygen release into working muscles, boosts endurance, reduces fatigue, and improves recovery.
Does VO₂ max only matter for athletes?
No. Research shows it is one of the strongest predictors of long-term health and lifespan. Everyone can benefit from improving it.
How can I work with The Breath Coach?
You can start with a free 15-minute consultation to discuss your goals. If you want to explore further, our Programs Insight gives a clear breakdown of the different ways we can work together. Whether you are an athlete in Europe, a professional in the USA, or someone in India looking to improve health and energy, our programs are designed to fit into your training and lifestyle.
Carbon monoxide rebreathing is one of the scientific tools that shows us how central haemoglobin and oxygen efficiency are to performance. While it is mainly used in specialist research or elite sports settings, the lessons it teaches apply to everyone. Your ability to use oxygen efficiently depends not only on your cardiovascular system but also on how you breathe.
Through structured breathwork training it is possible to significantly increase VO₂ max, improve recovery, and perform better under pressure. For athletes this means faster times and greater resilience. For professionals and everyday individuals it means more energy, better sleep, and stronger long-term health.
We work with clients internationally, from the UK to North America, Europe, and India, through online and in-person coaching.
If you would like to explore how breathwork can help you increase your VO₂ max and build resilience in both sport and life, book your free consultation today clicking on the blue button on this page.
