CO2 Tolerance Table

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Breathe In

Cycle 1 of 5

20 seconds per cycle

1 minute total

inhale

exhale

hold

10s

A freediving-style training breath that holds after a relaxed exhale to gradually raise your tolerance to carbon dioxide and calm the urge to breathe.

Cadence: 3 bpm
Difficulty: advanced
Family: Train
For: Performance

How to practice

1.Sit or lie down on dry land somewhere stable. Never in or near water, never standing, never while driving.
2.Breathe normally and calmly for a minute or two to settle; drop your shoulders and soften your belly.
3.After a relaxed, unforced exhale, hold your breath and begin a gentle mental count, stay completely still.
4.Let the first urges to breathe and the diaphragm 'twitches' come and go; this rising air hunger is the CO2 signal you are training, not an emergency.
5.When the urge becomes firm (but well before any distress) release and breathe normally, recovering fully.
6.Keep the hold length steady across rounds and shorten the recovery between holds a little each round; that accumulating CO2 is what builds tolerance. Stop the session if you feel faint, dizzy, or your heart pounds.

When to use this

As a focused, seated training block on dry land (for freedivers, spearos, or athletes who want to blunt the panic of air hunger) not as a quick calming tool, and never anywhere a blackout could be dangerous.

Benefits

Builds CO2 tolerance
Calms the panic reflex to breathe
Supports athletic performance
Trains breath-hold composure

Mechanism

When you hold your breath, oxygen slowly falls and carbon dioxide rises, and it is the rising CO2, sensed by chemoreceptors in the brainstem and arteries, not low oxygen, that triggers the urge to breathe and the involuntary diaphragm contractions. By repeatedly and safely sitting with that rising CO2, a CO2 table trains both your chemoreceptors and your conscious tolerance, so the same CO2 level feels less alarming over time. Holding after a relaxed exhale keeps your oxygen stores modest, so you reach the air-hunger zone quickly without driving oxygen dangerously low, the goal is tolerance, not oxygen deprivation.

Evidence

Breath-hold (apnea) training is well established in freediving, and there is real physiological research on the mammalian dive response, spleen contraction, and shifts in CO2 sensitivity with training. Evidence that it improves general, non-diving athletic performance is thinner and mixed. Treat it as a legitimate, sport-specific skill drill that carries genuine physiological stress. Not a proven health treatment, and not something to push toward your limit.

Lineage

CO2 tables come from competitive freediving and spearfishing, where 'dry' breath-hold training is standard preparation. Alongside O2 tables, they were formalised by apnea coaches and organisations such as AIDA as a structured way to raise tolerance to air hunger, drawing on the static-apnea tradition and the body's innate dive reflex.

Variations and progression

Classic fixed-hold table: keep the hold time constant and shorten the rest between holds each round.
Full-inhale version (holding after a full breath rather than after an exhale) for a gentler CO2 build.
Run the table against a metronome or a dedicated apnea-table app to keep timing honest and unhurried.

Start with short holds (perhaps 20–30 seconds) and generous recovery, and keep a log. Rather than chasing longer holds, tighten the recovery intervals gradually over weeks. Only progress when a whole table feels genuinely controlled and calm. Never combine breath-holds with water until dry practice is second nature and you have trained supervision.

Practice next

Common mistakes

Practising in or near water (the single most dangerous mistake), because shallow-water blackout causes silent drowning.
Chasing a longer hold or a personal best each session instead of building slow, controlled tolerance.
Tensing up and fighting the diaphragm contractions rather than staying relaxed and still through them.
Hyperventilating beforehand to stretch the hold, this hides the CO2 warning and raises blackout risk.

FAQ

Is the urge to breathe a sign I'm running out of oxygen?

No. It's driven mainly by rising CO2, which is exactly what you're training to tolerate. You still have oxygen in reserve when the urge begins, but that's never a reason to push toward the edge of a blackout.

How often should I train CO2 tables?

A few times a week at most, with rest days between. Daily maximal breath-holding is unnecessary and just adds strain.

Why hold after an exhale instead of a full breath?

Exhale holds reach the air-hunger zone faster and with less time, so you train CO2 tolerance efficiently, but they feel intense sooner, so ease in gradually.

Safety

NEVER practice breath-holds in or near water (even shallow water) because a shallow-water blackout leads to silent drowning. Never train breath-holds while driving.
Always train seated or lying down on dry land, somewhere you could safely rest if you did black out.
Do not do this if you are pregnant, or if you have cardiovascular or heart disease, high blood pressure, epilepsy, or any history of fainting or blackouts.
Never hyperventilate to extend a hold; stop immediately at dizziness, intensifying tingling, chest pain, or a pounding heart.
Learn from a qualified freediving instructor before doing any breath-holds in water, and never breath-hold train alone in water.

Breathwork is a complement to (not a replacement for) professional medical care. If you have a heart, respiratory, or blood-pressure condition, are pregnant, or feel unwell, check with a clinician before practising breath-hold techniques.