CO2 tables and O2 tables are two different breath-hold training protocols. CO2 tables keep the hold time constant while reducing rest intervals, training your tolerance to rising carbon dioxide. O2 tables keep rest constant while increasing hold time, training your body to function under lower oxygen levels. Both have a place in a freediving training plan, but they serve different purposes and carry different risks. Understanding the difference helps you pick the right one for your current level and goals.
CO2 tables and O2 tables are two different breath-hold training protocols. CO2 tables keep the hold time constant while reducing rest intervals, training your tolerance to rising carbon dioxide. O2 tables keep rest constant while increasing hold time, training your body to function under lower oxygen levels.
Both have a place in a freediving training plan, but they serve different purposes and carry different risks. Understanding the difference helps you pick the right one for your current level and goals.
CO2 tables: shorter rest, same hold
A CO2 table starts with a comfortable hold time, usually around 50% of your max static, and keeps it the same for every round. What changes is the rest interval, which gets shorter each round. By the final rounds, contractions arrive earlier and feel stronger because you start each hold with more residual CO2.
Here is an example CO2 table for a diver with a 3:00 max hold:
| Round | Rest | Hold |
|---|---|---|
| 1 | 2:00 | 1:30 |
| 2 | 1:45 | 1:30 |
| 3 | 1:30 | 1:30 |
| 4 | 1:15 | 1:30 |
| 5 | 1:00 | 1:30 |
| 6 | 0:45 | 1:30 |
| 7 | 0:30 | 1:30 |
| 8 | 0:15 | 1:30 |
The training effect is mostly psychological and neurological. You learn to stay composed when contractions hit earlier than expected. This carries over to depth dives where CO2 builds during ascent.
O2 tables: same rest, longer hold
An O2 table keeps the rest interval fixed (usually 2 minutes) while the hold time increases each round. This means your body spends progressively more time at lower oxygen levels, which trains the physiological response to hypoxia.
Here is an example O2 table for a diver with a 3:00 max hold:
| Round | Rest | Hold |
|---|---|---|
| 1 | 2:00 | 1:00 |
| 2 | 2:00 | 1:15 |
| 3 | 2:00 | 1:30 |
| 4 | 2:00 | 1:45 |
| 5 | 2:00 | 2:00 |
| 6 | 2:00 | 2:15 |
| 7 | 2:00 | 2:30 |
| 8 | 2:00 | 2:45 |
O2 tables carry more physiological risk than CO2 tables because you are deliberately pushing into lower oxygen territory. They should only be done on dry land or with direct supervision in a pool. Never do O2 tables alone in water.
Which one to train first
Start with CO2 tables. They are safer because the hold times stay moderate, and they build the contraction tolerance that most new freedivers need. CO2 work is also more relevant to everyday diving, where the urge to breathe during ascent is the main challenge.
Add O2 tables only once you have a solid CO2 tolerance base and understand blackout risk. O2 work is useful for competitive freedivers who need to extend their working time at depth, but it is not necessary for recreational diving.
How to build your own tables
Start with a recent max static hold done safely with a buddy. Set CO2 table holds at 50% of that max. Set O2 table starting holds at 33% and work up to around 90% of max by the final round.
Run 6 to 8 rounds per table. Dry tables are safe to practice alone at home, lying on the floor, in bed, or on a couch. Pool tables require a trained buddy watching. Never do tables in open water. One or two sessions per week is enough when combined with pool technique and coached depth work at schools in Dahab, Koh Tao, or Bali.
Common questions
Are O2 tables dangerous?
O2 tables carry more risk than CO2 tables because they push you into lower oxygen levels. Always do them on dry land or with a trained buddy in a pool. Never do O2 tables alone in water.
Can beginners do CO2 tables?
Yes, once you have a baseline max hold and understand the basics. Keep holds at 50% of max and stop if you feel faint or dizzy. CO2 tables are the safer starting point.
How often should you train tables?
One or two sessions per week is enough. Tables work best as a supplement to pool technique and coached open-water training, not as the main focus.
