The Oxygen Advantage for Freedivers

The Oxygen advantage is perhaps one of those books beginner freedivers (as well as experienced and especially instrucors) should pick up after completing their first course. Granted, much of what the author Patrick McKeown writes about is already mostly understood by freedivers, but there are some other specific gasses and chemicals, such as EPO and Nitric Oxide that are vital for freedivers to understand and how we can use them to our advantage.

The author also touches on the human bodies sensitivity to Carbon Dioxide, a gas we are all very well aware of, as well as why having a strong tolerance to Carbon Dioxide is beneficial to our body. After having experimented with the exercises prescribed in the book after taking something called the ‘BOLT’ test, it came surprising to me how easy Carbon Dioxide training can be with great results.

The Body Oxygen Level Test (BOLT) and the Bohr effect

The BOLT test is a simple test to determine the relative breathing volume during rest and breathlessness during exercise. The exercise is very simple; Hold your breath on FRC (Functional residual capacity) until you feel the first distinct urge to breathe.

A strong ventilatory response to carbon dioxide means the threshold will be reached sooner, resulting in a lower breath hold time. A good tolerance and reduced ventilatory response to carbon dioxide results in higher breath hold time.

When your BOLT score is lower, the breathing receptors are sensitive to carbon dioxide and the breathing volume will be greater as the lungs work to remove any carbon dioxide in excess to programmed levels. When you have normal tolerance to carbon dioxide and have a higher BOLT score, you will be able to maintain calm breathing during rest and physical exercise. Improving the BOLT score is best for physical endurance as having an improved tolerance to carbon dioxide means you will be able to better achieve a higher VO2 max.

If the BOLT score determines how sensitive a person is with carbon dioxide, this means there is s direct correlation with the Bohr effect. A high BOLT score means a reduced sensitivity to CO2, which results in better breathing which means an increase of CO2 in the blood. More CO2 in the blood causes the PH of the blood to drop which causes a right shift of the oxygen–hemoglobin dissociation curve, resulting in more oxygen available in the blood.

How understanding BOLT score as a freediving instructor is beneficial to understanding students breathing.

Once you dive into the book and understand how the Oxygen Advantage works, you will be able to understand and be more aware of your students breathing patterns. We’ve all done it before; ask the students to lie down face up with their eyes closed. As you begin to watch their belly, you will start to notice how fast they are breathing and how much. Generally, the calmer the breath with longer natural pauses the better they are accustomed to carbon dioxide.

Once you understand the rhythm of your students breathing you will begin to understand their sensitivity to carbon dioxide. As we know, an instructor / coach cannot prescribe the same set of exercises to a group of individuals. Exercises should be tailor made.

Three ways to increase your BOLT score.

  • Stop losses of carbon dioxide (breathe through your nose, stop sighing and avoid taking big breaths, observse your breathing throughout the day)
  • Improve your tolerance to carbon dioxide (refer to book)
  • Simulate High-altitude training (refer to book)

The important of nasal breathing

One of the ways on which to delay the first contraction during a breath hold is by breathing through your nose and yogi’s for thousands of years have been preaching this practice. I’ve always found a big difference when prepping for my dive on the water whilst sitting upright on the noodle, breathing in from the nose is always much more calming on my mind. It promotes breathing through the belly in a natural way.

Here are some benefits of nasal breathing:

  • It imposes approx 50 per cent more resistance to the air stream in normal individuals that mouth breathing
  • Warms and humidifies incoming air to the human bodies temperature
  • Removes germs and bacteria from the air you breathe in
  • During physical exercise allows for a work intensity great enough to produce aerobic training effect based on heart rate and percentage of VO2 max
  • It is a reservoir for nitric oxide, as essential gas for the maintenance of good health.

The importance of Nitric Oxide during nasal breathing

When it comes to nasal breathing and breath hold exercises, nitric oxide play an important role. Nitric oxide is produced in the nasal cavity and the lining of thousands of miles of blood vessels throughout the body. It is released in the nasal airways and transferred to the lower airways and lungs through nasal breathing.

Nitric Oxide plays an important role in:

  • The opening and closing of blood vessels
  • Homeostasis
  • Neurotransmission
  • Immune defence
  • Respiration

How to train carbon dioxide tolerance using the Oxygen advantage system

Training carbon dioxide should always feel easy, there is no point in hammering your body and system with very high levels of CO2. This is just going to create negative associations with CO2.

What’s smart about the Oxygen advantage system is the way the exercises are prescribed based on your BOLT score. So, the first thing you would need to do is measure your BOLT score. Once you have completed this task you know exactly where you stand. Here are some guidelines based on the BOLT score you achieve but please note that you must refer to the book.

Bolt score of 10 seconds:

  • Recovery exercise to unblock nose
  • Nose breath at all times
  • Avoiding sighing and taking big breaths
  • Breathe light to breathe right during rest
  • breathing recovery exercise.

Bolt score of 20 seconds:

  • Recovery exercise to unblock nose
  • Nose breath at all times
  • Avoiding sighing and taking big breaths
  • Breathe light to breathe right during rest and physical exercise.

Bolt score of 20 to 30 seconds:

  • Recovery exercise to unblock nose
  • Nose breath at all times
  • Breathe light to breathe right during rest
  • Simulate High altitude training during fast walk or jog.

Bolt score of 30 seconds or greater:

  • Nose breath at all times
  • Breathe light to breathe right during rest and physical exercise
  • Advanced simulation of high altitude training
  • Simulate High altitude training during fast walk or jog.

What are the benefits to the Oxygen Advantage system?

  • Improved sleep and energy
  • Easier breathing with reduces breathlessness during exercise
  • Naturally increased production of EPO and red blood cells
  • Improved oxygenation of working muscles and organs
  • Reduction if lactic acid build-up and fatigue
  • Improved running economy
  • Improved aerobic and anaerobic performance


This book is a must read for freedivers of all levels. Whilst the typical courses go into little detail, The Oxygen Advantage dives a little deeper and explains it in a very practical way. By adjusting a few things in your daily life and combining difference methods to work on your oxygen and carbon dioxide sensitivity, it doesn’t take much for the recreational / advanced freediver to improve on their breath hold. You will also learn to train in different ways; whilst walking, running or even whilst watching television which enables you to become more creative!