Advanced CO2 Tolerance Training Part 2 | Freedive Earth

Advanced CO2 Tolerance Training Part 2

Welcome back! Part 2 in this series on CO2 tolerance training deals with the use of Turnarounds, Technical issues in CO2 training and gives some examples for pool-based sessions. Hope you enjoy it. If you haven’t already, before reading this article you should look at our previous one which covers the basics of CO2 tolerance training. Improving your CO2 tolerance is probably the single best way to improve your breath-hold and overall freediving ability but it’s important to understand that by overdoing it, you’re likely to introduce bad habits into your technique, put yourself at risk of drowning and generally stress yourself out to the point of hating freediving altogether. Take it slowly. Don’t put yourself under any kind of stress until you’re sure that your technique is really solid, and don’t attempt any of the exercises described below unless you’ve:

  • Done at least one freediving course which involves CO2 training
  • Read the first article in this series
  • Practised and are confident with the basic level exercises described in it.

And remember, any kind of freediving activity in water, particularly the strenuous exercises described here, require the supervision of a qualified and competent freediving buddy.

Never, ever freedive alone!.

Using Turnaround Time in CO2 training

In the first article in this series we discussed the difference between a Rest Interval (where you get the same rest after each dynamic swim no matter how fast you do it) and a Turnaround Time where your rest is included in the time it takes you to complete each dive. For example:

 Turnaround Time in CO2 training


Clearly, the faster you do the dive, the more rest you’ll get because when you’re using a turnaround, the clock just keeps ticking. This is really useful. Much more useful, in fact, than a simple rest interval: If you’ve done any sort of formal freediving training, you’ll know that diving as fast as you can is generally a bad idea. Resistance in the water increases with the square of your speed through it, so you’re wasting a lot of energy by going faster.

That said, the quicker you do the dive (all other things being equal) the more oxygen you’ll have left at the end of it, and the further you’ll ultimately be able to go. Training with a turnaround time is ideal because it encourages you to make improvements, not just in pure speed which can leave you feeling exhausted and requiring a much longer rest interval than you’ll get, but also in efficiency. To put it another way, there’s an optimum speed for you to dive which minimises both your dive time, and the effort required to achieve it. Training with a turnaround pushes you to find that point for yourself. The key factor here, as you’ve probably guessed, is technique. More than anything else, good technique will help you minimise the effort you put in to a dive, and maximise your speed. We’re not going to discuss the specifics of technique in this article, check out our other posts (such as no-fins) for more information on this. But keep reading for more information about using Turnarounds to improve your technique.

Training for Technique with CO2 tables.

Every Freediver knows that the most important thing in Freediving is to always to look good in front of other people. This is a good enough reason for me at least to think about technique all the time. In addition to this, good technique can also (apparently) help you to dive deeper, further, longer and safer. Kind of like a good contraceptive. CO2 tables, particularly when you use a turnaround time rather than a rest interval are an ideal opportunity to focus on technical aspects of the dive for 4 main reasons:

  • You’ll be doing a large number of repetitive dives, so you can focus on one small aspect of technique.
  • Each dive is the same: You’ll be able to watch the clock and gauge your level of fatigue following each dive to see if you’ve made an improvement in speed and/or efficiency.
  • A useful change to your technique will yield you immediate benefit and make the session much easier and more enjoyable.
  • CO2 training is stressful - if you can maintain excellent technique during a period of stress, it will be much easier for you to do so in a competition environment, and towards the end of a maximum dive.

The key thing with technique is to develop Unconscious Ability. Once you’ve achieved this, you won’t have to think about that aspect of technique much at all. High volume training is the key to this, but you need to make sure you’re getting it right each time, otherwise you’ll just ingrain bad habits. Ideally, ask your buddy to watch the element you’re working on and give you feedback, otherwise go by the clock. If you’re going faster with less effort, you’re on the right track. Say you’re training for a no-fins event. On each training day choose one small aspect of technique (reaching fully forwards at the catch or keeping your head in the right position, for example). Build up slowly to peak intensity, including a large number of dives (see the examples below). This is called High Volume Training and for improving your technique there’s nothing better. As you’re diving, try to think about nothing else apart from the single, tiny technical point that you’re working on. Check your progress against the clock. If you’re going faster with less effort, you’re doing it right! On the next day, pick something else to work on, and do the same thing. Repeat until you achieve your chosen goal!

CO2 Tables - Live Examples

The examples shown below are Quite Difficult Don’t attempt these until you’ve tried and mastered the easier examples which you can find here. Remember Never Ever Freedive Alone! Simple Pyramid:

Keeping track of time can be difficult in these pyramids, particularly as you start to fatigue. Notice how each step of the pyramid comes at a whole number of minutes (e.g. 8x45sec = 360sec = 6min, 6x40sec = 240sec = 4mins). Organising things this way means that you can easily see when you need to move on to the next set and helps you to work out when you should be going next. Intense DNF Pyramid with ‘Sawtooth’ Pattern:

The principle here is that you won’t be able to maintain the maximum intensity (e.g. 30sec turnaround) for long. Adding a lower intensity phase into the middle allows you to stay at peak intensity for a much longer proportion of the set. You can get creative too: Try adding extra blocks of work, or working on maximum speed for the same level of work: 

Technical Considerations

Remember that maintaining good technique under pressure is one of the key aims of this type of training. Inevitably, as you get up towards maximum intensity, you’ll begin to fatigue and your technique will start to come a little bit unstuck (if it isn’t, you’re probably not working hard enough!). This is one of the main reasons why you need a very good level of technical ability before you even think about pushing yourself to the max. Whatever type of CO2 training you’re doing, one of the key times to focus on technique is during the ‘cool-down’ phase of the workout - as you’re coming down the other side of the pyramid. In the ‘intense’ example above, for instance, the second set of 12 dives on 35sec will still be hard, but if you’ve chosen your table right, you’ll find that you’ve got just enough rest for it not to be overwhelmingly stressful. This simulates quite accurately the feeling you’ll get towards the middle or the end of a maximum attempt - lots of lactic, a bit of hypoxia and some mental stress in thinking about how far you’ve still got to go. If you get used to nailing your technique in these conditions, it will only bring benefit in competition. That’s it for this week, next week we’ll look at CO2 training for depth. See you next time :) Got a training tip you’d like to share? Comment below or write to us at or here.

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