Breath-hold training

CO2 Tables (CO2 Tolerance Training)

Same hold every round, less rest each time. You learn to stay calm while the urge to breathe builds.

Also called: CO2 table, CO2 tolerance table, Carbon dioxide table, Hypercapnic table

A CO2 table is a freediving dry-training drill: a series of breath-holds of the same length, usually eight, with less rest between them each round. Because the rest keeps shrinking, carbon dioxide builds a little more before every hold, and the urge to breathe comes sooner and stronger.

You practice staying still and loose through that urge. Done lying down on dry land, it turns the urge to breathe from an alarm into something familiar. It is training for freedivers and breath-hold athletes, not a relaxation exercise.

Pattern: Fixed hold, shrinking rest. Spoon default: eight 2:00 holds, rest from 2:00 down to 0:15
Session: About 25 minutes at Spoon's default
Good for: Freediving and breath-hold training, not relaxation
Level: Intermediate to Advanced
Origin: Freediving dry training, no single inventor
Needs: iPhone or Apple Watch

How to do it

Lie down on a bed, couch or floor, on dry land and away from water. Set your numbers before you start.
Breathe normally for a minute or two. Do not breathe faster or deeper than usual.
Rest: breathe calmly and normally for the round's rest time.
At the end of the rest, take one full, relaxed breath in. Not a gasp.
Hold. Keep your body still and your shoulders and jaw soft. Diaphragm contractions are expected as the urge to breathe builds.
Breathe again when the hold time ends, or sooner if you need to. Take one or two easy recovery breaths.
Repeat for every round. The hold stays the same; only the rest gets shorter.
After the last hold, stay lying down and breathe normally for a minute before you stand up.

Benefits

Calm when the urge to breathe hits
You meet the urge to breathe again and again in a safe setting, so it stops feeling like an alarm and starts feeling familiar.
Steady under pressure
Each hold asks you to relax while discomfort builds. That steady, unhurried feeling stays with you after the session.
Sharp, quiet focus
During a hold there is one job: stay still. You finish clear-headed and focused.

What the research says

CO2 and O2 tables are standard freediving dry training; the Molchanovs freediving school lists them among the key areas to train at home^[2]. On a full breath, the urge to breathe comes mainly from rising carbon dioxide. The Divers Alert Network warns that hyperventilating before a hold delays that urge and raises the risk of losing consciousness^[6].

Breath-hold training does change the body over time. A 2021 review reports that trained breath-hold divers have a stronger diving response than non-divers, mainly as a result of training^[5].

The table format itself has thin support. In a 2024 study, 28 people new to breath-holding did maximal holds, a CO2 table and an O2 table in random order^[4]. Maximal holds lowered blood oxygen more than either table, and the rise in carbon dioxide did not differ between them. The authors suggest beginners focus mainly on maximal holds^[4].

Hold times also rise fast within one session, and lower CO2 sensitivity does not explain it. When 14 volunteers did five maximal holds in a row, their hold time rose 43 percent, yet their breathing response to carbon dioxide did not change^[3]. The table is a common, structured drill, not a proven best method.

CO2 table vs O2 table

CO2 table: the hold stays the same and the rest shrinks each round^[1]. Every hold starts with more carbon dioxide left over, so you train comfort with the urge to breathe.
O2 table: the rest stays the same and the hold grows each round^[1]. Oxygen drops lower, so it is the more advanced of the two.
Build comfort with CO2 tables first. Never do both on the same day, and keep each one to two or three sessions a week^[1].

How to choose your hold time

Spoon does not test your maximum or build the table from it. You choose the hold, from 30 seconds to 4 minutes, and it stays the same in every round. Pick a hold you can finish calmly, well under your best. The 2:00 default assumes real breath-hold experience; if 2 minutes is near your limit, start lower and build up in 15-second steps.

Tips

Keep rest breathing normal. Bigger or faster breaths before a hold only hide your warning signs.
If every round turns into a fight, your hold is too long. Lower it by 15 seconds.
When you start out, set the hold so most rounds end before your first contraction. Build from there.

Safety

Dry land only. Never practice in or near water, not even in a bathtub. A blackout in water is silent and can be fatal.
Never do breath-hold training in water alone. Even in a pool, breath-holding needs dedicated one-on-one supervision^[6].
Never practice while driving, operating machinery or standing. Lie down: if you faint in a chair or on your feet, you can fall and get hurt^[1].
Never hyperventilate before a hold or during the rests^[6]. That includes fast breathing, such as Wim Hof rounds, right before a table.
Stop and breathe at any dizziness, tingling, ringing in your ears or change in vision.
Ask a doctor first if you are pregnant or have a heart condition, uncontrolled blood pressure, a seizure disorder or a history of fainting.

CO2 Tables in Spoon

Spoon runs CO2 Tables on iPhone or Apple Watch. You set the rounds, the hold, the starting rest and how much the rest shrinks, and Spoon times every rest and every hold for you. A bell marks each change, so you never have to watch the clock.

On Apple Watch, one tap pattern starts each hold and a different one starts each rest. With your Watch on, you see your heart rate live. Sessions save to Apple Health as Mindful Minutes, never as workouts.

Default table: 8 rounds, a 2:00 hold, rest from 2:00 down to 0:15, about 25 minutes.
Adjust Rounds (4 to 12), Hold Time (30 s to 4 min), Starting Rest (15 s to 3 min) and Rest Decrease (5 to 30 s per round).
Rest Mode can count breaths instead of seconds, from 2 to 10 breaths.
A bell at every change between rest and hold. There is no voice.
End any hold early with a tap; the target is a plan, not a rule.
After the session, Spoon charts the hold you actually did in every round.

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Questions

What is the difference between a CO2 table and an O2 table?

In a CO2 table the hold stays the same and the rest gets shorter each round, so you train comfort with rising carbon dioxide and the urge to breathe. In an O2 table the rest stays the same and the hold gets longer, so oxygen drops lower. Freedivers build a base with CO2 tables first and never do both on the same day.

How long should CO2 table holds be?

Use a hold you can finish calmly, well below your best breath-hold, sized from your own numbers. Spoon's default is 2 minutes, which assumes real breath-hold experience. If that is near your limit, start lower. If every round becomes a fight, shorten the hold.

How often should you do CO2 tables?

Two or three times a week is the usual guidance, with rest days in between, and never on the same day as an O2 table. Progress comes from weeks of steady, calm practice, not from one hard session.

Are CO2 tables safe?

Only on dry land and lying down, with normal breathing between holds. In or near water they are dangerous: a blackout there is silent and can be fatal. Never practice in water alone, never while driving and never right after fast breathing. Ask a doctor first if you are pregnant or have a heart, blood pressure or seizure condition.

Do CO2 tables increase breath-hold time?

They train you to stay relaxed through the urge to breathe, a big part of holding longer. The evidence for the table format itself is limited: in a 2024 study of beginners, tables lowered oxygen less than plain maximal holds, and the authors suggested beginners focus on maximal holds.

Sources

Apnealogy. How To Use Freediving Tables: Your Guide to Breath-hold Training. Apnealogy. apnealogy.com
Molchanovs. Freediving Dry Training: 5 Key Areas to Work On. Molchanovs. us.molchanovs.com
Andersson JP, Schagatay E. Repeated apneas do not affect the hypercapnic ventilatory response in the short term. European Journal of Applied Physiology, 2009. pubmed.ncbi.nlm.nih.gov
Declercq L, et al. A dive into the physiological responses to maximal apneas, O2 and CO2 tables in apnea novices. European Journal of Applied Physiology, 2024. pubmed.ncbi.nlm.nih.gov
Elia A, et al. Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review. European Journal of Applied Physiology, 2021. pubmed.ncbi.nlm.nih.gov
Divers Alert Network. Hypoxia in Breath-Hold Diving. Alert Diver, DAN. dan.org

Updated October 2026. This page is for education, not medical advice. If you have a heart, lung or blood pressure condition, epilepsy, or you are pregnant, ask your doctor before you start a breathing practice with holds or fast breathing.