As far back as I can remember, I always wanted to breathe.
As a matter of fact, I started to breathe quite young and it quickly became a daily habit that I intend to keep doing until late in my life
Of course, as I've been teaching scuba diving for 45 years now, I know that most divers enjoy breathing on a regular basis, usually around 20.000 times a day, but it's only recently - as I discovered the Buteyko method and Patrick McKeown's Oxygen Advantage - that I realized that we don't always breathe as efficiently as we should. And that, my friend, could be a problem underwater!
If you are a diver, and even more if you are a rebreather diver, breathing is what keeps you alive underwater, as it is not only essential to bring oxygen to your cells and eliminate the by-product of the metabolism, but is also intimately linked to your nervous system. Diaphragmatic nasal breathing keeps you calm and relaxed, while mouth breathing using only your upper chest immediately creates a state of low-grade stress similar to wearing a new white shirt at a painting class for hyperactive toddlers.
Because of the equipment we use, we mouth breathe underwater. Combine that with the fact that we move in an environment that is alien to us, and we end up with a nervous system ready to turn a simple stressful problem into a panic situation. Breathing rate increases, making air hunger and susceptibility to hyperventilation an experience that most divers would prefer to avoid.
A rebreather diver is even more prone to this situation than an open-circuit diver, as rapid shallow breaths can quickly end up in a CO2 build-up that can become critical at depth. Breathing pattern matters enormously underwater: it governs scrubber duration, work of breathing, CO2 loading, and how calm a diver feels when something goes wrong. The Oxygen Advantage method is built on one core idea that applies directly to this problem: most people breathe more air than their body needs, and training the body to tolerate slightly more CO2 produces slower, lighter, more efficient breathing — with less perceived breathlessness, not more.
Why this matters on a loop
The central mechanism is the Bohr effect: carbon dioxide is what signals red blood cells to release oxygen into tissue. Breathe too fast or too heavily and CO2 is washed out before it can do that job, so oxygen clings to hemoglobin instead of reaching muscles and brain, even though "more air" was taken in. The fix isn't deeper breathing; it's calmer, lighter breathing that lets CO2 settle into a healthier range. For a rebreather diver, the practical payoff is real: a diver with poor CO2 tolerance breathes fast and shallow at the first sign of exertion or stress, which increases work of breathing, accelerates scrubber consumption, and — critically — makes it harder to distinguish ordinary exertion from an actual hypercapnia event.
The goal here is a calmer resting breathing pattern in the water, not tolerance used to override real symptoms of scrubber failure, elevated pCO2, or channeling. If you ever feel headache, air hunger that won't ease, or confusion on the loop, treat it as a bailout indication, not something to breathe through.
With that boundary in place, three land-based exercises from the Oxygen Advantage method build the raw skill that transfers into calmer, more efficient breathing at depth.
Three exercises to build underwater breathing efficiency
1. The BOLT score test (Body Oxygen Level Test). After a normal (not deep) exhalation, pinch your nose and time how long you can comfortably hold before the first definite urge to breathe — a throat twitch or involuntary abdominal contraction, not a maximal breath-hold. The BOLT score measures your sensitivity to carbon dioxide and breathing efficiency. A score under 20 seconds suggests a breathing pattern that runs "hot" — quick to feel breathless under load, which is exactly the pattern you don't want mid-dive. A good score is above 40 seconds. Testing your BOLT score every few weeks gives an objective, trackable baseline for whether your training is actually improving your CO2 tolerance.
2. Breathe Light to Breathe Right. Sit or lie comfortably, breathe only through the nose, and gently soften and slow each breath until the fine hairs in your nostrils barely move. Let a mild, tolerable "air hunger" build on both the inhale and exhale, and hold that quiet rhythm for three to five minutes, easing off if breathing ever feels rushed or panicky. This is the foundational drill for correcting chronic over-breathing, and it's the closest topside analogue to the relaxed, minimal-effort breathing pattern you want on a mouthpiece: soft, slow, low-effort, no gasping.
3. Breath holds during light movement (CO2 tolerance training). Walking or lightly jogging, exhale normally, hold, and keep moving until a strong but controlled air hunger appears, then recover with slow nasal breathing before repeating four or five times. This trains tolerance to rising CO2 and falling oxygen — the exact physiological state a hard-working diver experiences — without ever removing the diver's ability to sense a genuine problem. Over four weeks this measurably raises the workload a diver can sustain before breathing becomes ragged, which is precisely the failure mode you want pushed further out on a rebreather.
Bringing it into the water
None of these drills are done underwater. They are topside conditioning — the same way divers train fitness on land before they show up on a dive. What transfers to the rebreather is the pattern: slow, diaphragmatic, nose-like softness even though you are breathing through a mouthpiece, and a nervous system that doesn't spike into rapid shallow breathing the moment CO2 rises or a task gets stressful. A diver who has built this baseline tends to:
Breathe the loop more slowly and efficiently
Extend their scrubber duration
Work less hard for the same output
Stay calmer and more in control if something in the breathing loop, the environment, the equipment, or another diver, goes wrong.
Don't take breathing for granted. It's an essential, but easy to train, component of every dive. Rebreather divers don't always realize that improving their mental state and physiological performance is one of the most efficient ways to deal with anything that may happen during their dives.
About the author:
After serving as a PADI Examiner and Regional Manager, Cedric "Vic" Verdier turned to technical diving, pushing the limits of deep and cave exploration. He was the first to dive the wreck of the battleship HIJMS Yamashiro at -196m/645ft in the Philippines, and has explored numerous other deep wrecks worldwide, including the submarine Protée, the s/s Natal in France, and HMS Manchester in Tunisia, as well as sub-200m/650ft cave systems across Southeast Asia. The author of nine books on diving, he now lives in the US, where he works as a Cave, Trimix, and Rebreather Instructor Trainer.
As a matter of fact, I started to breathe quite young and it quickly became a daily habit that I intend to keep doing until late in my life
