If you have spent any time around breath-hold training, you have heard about CO2 and O2 tables. They look similar on paper, a column of holds and rests, but they pull on two completely different physiological levers. Knowing which lever you are pulling keeps your training focused and your progress measurable.
What a CO2 table trains
A CO2 table holds your breath-hold duration roughly constant while steadily shortening the rest period between rounds. With each round you start the next hold a little more loaded with carbon dioxide, so your body learns to stay calm as that familiar urge to breathe arrives earlier and earlier. The goal is mental and physical tolerance, not a longer maximum hold.
- Holds stay similar in length, often a comfortable percentage of your max
- Rest periods get progressively shorter each round
- The challenge builds gradually rather than peaking at the end
What an O2 table trains
An O2 table flips the pattern. Rest stays generous and fixed, while each breath-hold grows longer than the last. Because you recover fully between rounds, the work happens inside each hold, where your body practises operating with steadily falling oxygen. This is the table that nudges your apnea ceiling upward over time.
- Rest stays the same length for every round
- Each hold is a little longer than the previous one
- The final rounds feel hardest because oxygen demand peaks late
A simple way to remember
CO2 tables move the rest, O2 tables move the holds. One teaches comfort with the breathing urge, the other extends raw capacity.
Choosing and sequencing them
Most freedivers run one table type per session and never stack both in a single day, because the recovery demands and fatigue patterns are different. A common rhythm is to alternate types across the week and to base your numbers on a recent, honest assessment of your comfortable hold rather than an all-out personal best.
Dry training only
CO2 and O2 tables are designed for dry land, performed seated or lying down. Never run them in water, in a bath, or while moving around alone. A hypoxic blackout in water is silent and can be fatal. In water, always train with a trained, attentive buddy.
Use these tables as steady, repeatable building blocks. Track how each one feels, progress conservatively, and let comfort, not ego, set your numbers.