CO2 and O2 Tables: The Dry Training That Actually Moves Your Breath-Hold
Two tables, two different adaptations, and a hard rule about where you do them. One trains tolerance to discomfort, the other trains efficiency at low oxygen, and confusing them wastes weeks.
Wednesday, August 12, 2026/3 min read
Apnea tables are the most widely used dry training tool in freediving and the most widely misunderstood. People run them daily, mix the two types together, and wonder why nothing improves.
The two tables train different things, and the difference is the whole point.
The safety rule first
Both are dry training. On a sofa, on the floor, in a chair. Never in water, never in a bath, never in a pool, never alone in any of those places.
A blackout on dry land is frightening and survivable. The same blackout face down in fifteen centimetres of water is a drowning. This is not a theoretical caution; it is the most common way breath-hold training kills people.
CO2 tables: tolerating the alarm
A CO2 table keeps the hold length constant and shortens the rest between holds.
Because you never fully clear the carbon dioxide from the previous hold, it accumulates. Each successive hold starts with more CO2 in the system and therefore feels harder, even though it is the same duration.
What that trains is tolerance: staying relaxed while the urge to breathe builds, and not panicking through diaphragm contractions. It is largely psychological and it works quickly, within weeks.
A typical structure, using a comfortable hold of around half your maximum:
- 8 rounds of a 1:30 hold
- Rest starting at 2:00 and dropping by 15 seconds each round, down to 0:45
It should be uncomfortable by round five and genuinely hard by round eight. If it is not, the hold is too short.
O2 tables: working at low oxygen
An O2 table keeps the rest constant and lengthens the hold.
Rest is generous, usually two minutes, so CO2 clears between efforts. The holds get progressively longer, so each one takes you further down the oxygen curve.
This trains the body to function with less available oxygen and encourages the adaptations that matter: stronger dive reflex, spleen contraction releasing extra red cells, better peripheral vasoconstriction.
A typical structure, working from around 50 percent of maximum up towards 80:
- 6 rounds, rest fixed at 2:00
- Holds of 1:30, 1:45, 2:00, 2:15, 2:30, 2:45
The early rounds should feel easy. The last two should not.
How to schedule them
The mistake almost everyone makes is doing both, every day, at maximum effort.
O2 tables are demanding and need recovery. Twice a week is plenty. CO2 tables are less taxing and can be done three or four times a week. Never run both in the same session, and leave at least a day after an O2 table.
A workable week: CO2 on Monday, O2 on Tuesday, rest Wednesday, CO2 Thursday, O2 Saturday.
Reassess your maximum every four to six weeks rather than testing it constantly. Maximum attempts are the least useful training there is: they are exhausting, they carry the most risk, and they teach very little.
Doing them properly
Prepare each hold with the same slow diaphragmatic breathing you would use in the water, and never with hyperventilation, for reasons we set out in the piece on breathing technique. Lower starting CO2 delays your warning without adding oxygen, which defeats the purpose of a CO2 table entirely and makes an O2 table dangerous.
Stay still. Movement burns oxygen and contaminates the result.
Do not chase numbers on the day. Tables are a stimulus, not a test, and a session where you complete every round comfortably is a session that was correctly calibrated.
What tables will not do
They will not fix your equalisation, which is what actually stops most people getting deeper. Depth progression is limited by the ears far more often than by breath-hold, and no amount of dry apnea changes that: that problem has its own solution.
They will not teach you to relax in open water, where cold, depth and the sight of a line disappearing below you all change the experience.
And they are not a substitute for supervised training. Tables build the engine. The diving is still done with a buddy on the surface watching you.
This article is general information, not medical advice or a substitute for certified instruction. Anyone with cardiovascular, respiratory or blood pressure conditions, and anyone pregnant, should talk to a doctor before breath-hold training.
Published in The Outspoken Digest
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