O2 Tables for Freediving: Building Hypoxic Tolerance Safely
An O2 table keeps the rest fixed and stretches each hold, training your body to cope with less oxygen. Example table, safe ceilings and how often to use it.
An O2 table is a set of dry breath-holds where the rest between holds stays fixed, usually at two minutes, and the holds get longer each round until they reach about 80% of your personal best. Because each hold goes further into low oxygen, it trains your tolerance to hypoxia rather than to carbon dioxide. It is more demanding than a CO2 table, so you do it less often, always lying down on land and never in water.
For most beginners, the O2 table is the second tool, not the first. It works best once a few weeks of CO2 tables and relaxation holds have made contractions feel familiar.
What an O2 table trains, and why it needs more care
In a CO2 table, short rests mean carbon dioxide builds up while the holds stay modest. In an O2 table, the full two-minute rests let you clear most of the CO2 between rounds, so each hold starts fresh. What changes is how far into the hold you go. The later rounds take you to lower oxygen levels than everyday training does.
Over time, that is thought to help your body handle hypoxia: a more pronounced dive response, a calmer reaction to the late stage of a hold, and familiarity with what the final part of a long breath-hold feels like. The research on exactly which adaptation comes from which kind of table is thinner than the confident tone of the internet suggests, but the general approach is standard in freediving training.
The risk comes from the same place as the benefit. Low oxygen gives very little warning, and your urge to breathe is driven by CO2, so you can feel fine until the moment you are not. That is the mechanism behind shallow water blackout, and it is why O2 work happens on a bed or a mat, never in water. Our explainer on why CO2, not O2, drives the urge to breathe covers the physiology.
How an O2 table is built
- Rest: fixed at 2:00 every round.
- Holds: start at roughly 40–50% of your personal best and get longer each round.
- Increase: about 10 seconds per round for PBs under three minutes, 15 seconds for longer PBs.
- Ceiling: the longest hold is about 80% of your PB. Beginners should cap it at 70–75% for the first few weeks.
- Rounds: eight is typical. Once you reach the ceiling, repeat it rather than going beyond it.
Example O2 table for a 2:30 personal best
Eighty percent of 2:30 is 2:00, so 2:00 is the ceiling.
| Round | Rest before the hold | Hold |
|---|---|---|
| 1 | 2:00 | 1:00 |
| 2 | 2:00 | 1:10 |
| 3 | 2:00 | 1:20 |
| 4 | 2:00 | 1:30 |
| 5 | 2:00 | 1:40 |
| 6 | 2:00 | 1:50 |
| 7 | 2:00 | 2:00 |
| 8 | 2:00 | 2:00 |
The full table runs to about half an hour. If O2 tables are new to you, stop after round 6 for your first couple of sessions, which keeps your longest hold at around 73% of your PB.
Ceilings for other personal bests
| Personal best | 70% ceiling | 80% ceiling |
|---|---|---|
| 1:30 | 1:03 | 1:12 |
| 2:00 | 1:24 | 1:36 |
| 2:30 | 1:45 | 2:00 |
| 3:00 | 2:06 | 2:24 |
| 4:00 | 2:48 | 3:12 |
Round down to the nearest five seconds when you programme it. Nobody needs a 1:03 hold.
Why O2 tables happen less often than CO2 tables
A CO2 table is uncomfortable but stays far from your limits. An O2 table spends its last few rounds much closer to them, and your body takes longer to bounce back. A sensible frequency looks like this:
- Beginners: one O2 table a week at most.
- Experienced divers: one or two a week, depending on the rest of their training.
- Never on the same day as a CO2 table, a maximum static attempt or a dive day.
- Not the day before a big pool session or a flight to the coast.
If two minutes isn’t enough to recover, the usual fix is to lower the ceiling rather than lengthen the rest, which would turn it into a different and less useful session.
Signs you are overdoing it: headaches after sessions, disturbed sleep, a static PB that is going backwards, or dreading the session. A week off often fixes all four. Our post on sleep and recovery for freedivers covers what proper rest looks like.
How to run an O2 table safely at home
- Pick a day when you slept well and haven’t eaten for two to three hours.
- Lie on your back on a bed or a mat on the floor. Not a sofa, not a chair, not the edge of anything.
- Tell someone at home what you are doing, especially for the later rounds. They don’t need to watch; they need to know.
- Set the table up in a timer app with a voice countdown, and keep your eyes closed.
- Breathe up calmly in each two-minute rest. No hyperventilation, no packing.
- In the long holds, stay passive. The final 20 seconds should feel like effort, not like a fight.
- Finish each hold with two or three recovery breaths before settling into the rest.
Some people like to clip on a pulse oximeter during dry tables. That is fine out of curiosity, but don’t treat the number as a safety line. Finger oximeters lag behind what is happening in your blood and become less accurate at low readings.
Warning signs that should end the session
- Tunnel vision, greying or flashing lights
- Twitching, jerky movements or shaking as you start breathing, a land version of samba, or loss of motor control
- Feeling confused, disoriented or not quite yourself after a hold
- A strong headache, nausea or chest discomfort
Any of these means the table is too aggressive. Stop, rest, and next time drop your ceiling by about 10%. If you lose consciousness, even briefly, pause O2 training and talk to a coach, and a doctor if you have any doubt, before doing more. Chest pain, palpitations or repeated fainting need a doctor.
Safety: O2 tables are a dry, land-only exercise, done lying down. Never do them in a bath, a pool or the sea, and never alone in water of any depth. A faint on a mattress is a scare. The same faint with your face in water is how people drown.
When an O2 table is the wrong tool
- If your holds end within the first minute because of discomfort, you need relaxation work and CO2 tables first.
- If you have been ill, slept badly, or it is a sweltering May afternoon and the power has gone, skip it.
- If you have a heart condition, high blood pressure or epilepsy, or are pregnant, ask your doctor before doing any breath-hold training.
Fitting an O2 table into your training week
A simple week for someone a month or two into dry training: CO2 table on Monday, easy cardio on Tuesday, O2 table on Thursday, relaxation holds and stretching on Saturday, and the other days off. That is enough for steady progress without wearing you down. For a full progression that adds pool sessions, flexibility and cardio, see our 8-week freediving training plan for beginners.
Keep a note of your ceiling, your last two rounds and how you felt afterwards, and only move your ceiling up towards the 80% limit when two sessions in a row end with the final hold feeling controlled. We’re building an online community for Indian freedivers. It’s coming soon, so stay tuned.
Frequently asked questions
Should beginners do O2 tables?
Not straight away. Most beginners gain more from relaxation holds and CO2 tables for the first few weeks, because discomfort from rising carbon dioxide is what ends their holds. Once contractions feel familiar, adding one O2 table a week with a ceiling of 70 to 75% of your personal best is a sensible, conservative start.
How long should the rest be in an O2 table?
Two minutes is the standard rest, and it stays the same every round. That is long enough to clear most of the carbon dioxide from the previous hold, so the table targets low oxygen rather than high CO2. If two minutes isn't enough for you to recover, lower your ceiling instead of stretching the rest.
Can you pass out during a dry O2 table?
Yes, it is possible, especially if you set the ceiling too close to your maximum, train when tired or hyperventilate before the holds. That is why O2 tables are done lying on a bed or the floor, with someone at home aware of what you're doing, and never in water. If you do faint, stop O2 training and get advice before resuming.
Is a CO2 table or an O2 table better?
Neither is better, because they train different things. A CO2 table builds tolerance to the urge to breathe with fixed holds and shrinking rests. An O2 table builds tolerance to low oxygen with fixed rests and longer holds. Most training programmes use both, with CO2 tables more often and O2 tables once a week or less.
