CO₂ tables for freediving are the workhorse of dry apnea training: a structured set of fixed-length breath holds with steadily shrinking rests that teach you to stay calm as the urge to breathe builds. For spearfishers, that translates straight into longer, more relaxed bottom time. This guide shows you exactly how a CO₂ table is structured, gives you a sample table you can run today, walks through what a session actually feels like, lays out an eight-week progression, and flags the common mistakes that stall progress.
What a CO₂ Tolerance Table Trains
The discomfort that ends most dives isn't a real oxygen emergency — it's your brain reacting to rising carbon dioxide. The diaphragm contractions, the burning, the urge to surface: that's CO₂ tolerance talking, and it's trainable. A CO₂ table deliberately lets carbon dioxide accumulate across the set so you spend time in that uncomfortable zone and learn to relax through it.
This is the single most useful adaptation for reef spearfishing, where you rarely need a maximal hold but constantly benefit from a calmer, later urge to breathe. CO₂ tables fit into the broader system explained in Breath-Hold Tables: The Complete CO₂ & O₂ Guide.
How a CO₂ Table Is Structured
The defining feature of a CO₂ table is simple: the hold stays the same length every round, while the rest period shrinks. Because each rest is shorter, you never fully clear the CO₂ from the previous hold, so it stacks up. By the final rounds, a hold you barely noticed at the start feels genuinely hard — without your oxygen ever getting dangerously low.
A standard table is eight rounds. The hold is set to a moderate fraction of your maximum — usually around 55–75% — so it's challenging but never near your limit. Only the rests change.
A Sample CO₂ Table You Can Use
This example assumes a relaxed max hold of about 3 minutes, with the working hold set at a comfortable 1:30. Notice the hold never changes; only the rest comes down.
| Round | Breathe-up (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 |
Scale the hold to your own max rather than copying these numbers blindly — the method for deriving it is in How to Make a Breath-Hold Table, Step by Step.
What a Session Actually Feels Like
Knowing the feel of a good CO₂ table helps you judge whether yours is set right. Rounds one to three should feel almost too easy — you finish each hold well before any real discomfort. Around round four or five the contractions begin: small involuntary twitches of the diaphragm that signal rising CO₂. By rounds seven and eight, those contractions are strong and close together, and the work is entirely mental — staying loose, keeping your shoulders and throat relaxed, and not counting down the seconds. You should finish the table tired of the burn but never light-headed. That arc — easy, then contractions, then a mental fight — is the signature of a correctly scaled CO₂ table.
An Eight-Week CO₂ Progression
Don't make holds longer every session — progress the table in small, planned steps and let adaptation catch up. A simple block looks like this:
| Weeks | Adjustment | Goal |
|---|---|---|
| 1–2 | Fixed hold at ~50% of max, rests 2:00 → 0:15 | Learn the rhythm; finish all 8 rounds easily |
| 3–4 | Raise the fixed hold by 10–15s | Contractions by round 5, still controlled |
| 5–6 | Re-test max, rescale hold to ~60% | Last two rounds a real mental fight |
| 7–8 | Tighten the final rests (0:20 → 0:10) | Hold steady relaxation under heavy CO₂ |
If a week feels too hard, repeat it rather than pushing on. Progress in apnea is rarely linear, and forcing it just raises your risk.
How Hard Should It Actually Feel?
The first three or four rounds should feel almost easy. Contractions should begin somewhere in the middle of the table and grow stronger toward the end, so the last two rounds are a real mental fight to stay relaxed — but you should never feel light-headed, never see stars, and never approach a blackout. If you do, your hold is set too long. CO₂ tables are about discomfort, not danger.
Common CO₂ Table Mistakes
- Setting the hold too long. A CO₂ table is defined by shrinking rest, not by long holds. If you're fighting from round two, shorten the hold.
- Hyperventilating in the rests. This strips CO₂ and masks blackout warning signs — exactly backwards for this table.
- Doing them too often. CO₂ tolerance work is a stress that needs recovery; spacing matters, as covered in how often to do CO₂ and O₂ tables.
- Mixing in O₂ work the same day. Never run a CO₂ and an O₂ table in one session — see CO₂ vs O₂ tables for why.
- Tensing up under contractions. Clenching your jaw, throat, or shoulders burns oxygen and breaks your calm. The skill is staying soft while the diaphragm fires.
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