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Question Would you say co2 tolerance is both mental and physical or just mental?


New Member
May 18, 2024
Hello, everyone. I'm new here.

So I'm wondering if co2 tolerance is purely a mental skill (relaxation, stress management), or if there is also any physiological or physical adaptation from constantly holding one's breath.

To my understanding, and I apologize for bringing this up, certain people suffer from chronic respiratory acidosis, meaning they experience higher than average co2, and the body compensates by keeping bicarbonate and other buffers in the blood. My question is if these adaptations could be emulated by breath-holding.

From your experience, would you say your improvements have been only mental? Or the body also adapts?

My PB static is 4:40, which I have no idea how I even achieved, it was pure suffering and I weighed a bit less, but that was like my third time holding my breath seriously. I'm not able to replicate this so far, even with hyperventilation I only achieve 4 minutes and that's difficult. This leads me to assume that I'm physically overtrained, even when I feel motivated I have difficulty reaching 3 mins.

And just to clarify, I know that hyperventilation under water is a BIG NO NO. I'm only interested in static PB's, on my bed. Sorry for the long ahh text.
Adaptations from (and for) breathhold...

I'd have to say there are some adaptations from practicing breathholds, and that improvements do go beyond only mental (though that clearly plays a very significant role). For example, it certainly seems as though practicing BH leads to the dive response activating more easily and more strongly - in particular, spleen contraction is noticeably stronger for experienced BH divers (see refs below).

Also, in a slightly different form of 'adaptation', some of the stretching exercises that freedivers use can help the chest and breathing muscles (diaphragm, intercostals, etc.) to allow increased (comfortable) lung capacity at the final breath (i.e. more oxygen stored in lungs for use during BH).

In a previous post I cited a few articles that mention adaptations for BH, so I'll link that here:
The following post in the same thread also cites some articles concerning the spleen (as well as other vaguely related things):
Check out this post for more articles that might be of interest:

'Suffering' through breathhold...

It sounds like your early longer BH time(s) may have come from an initial determination, perhaps combined with less expectation & experience of the 'suffering' from any previous long BHs - and my guess would be that, since then, you've fairly often gone through more of that 'pure suffering' in an attempt to repeat such times...?

I've posted before about the importance of enjoying & having fun with BH (rather than treating it like training for some adrenaline-fuelled sport!), and some parts of that may be relevant here, so I'll point to that rather than repeating myself here:
See also various replies in this thread:


Regarding hyperventilation, despite the lower (initial) CO2 that would seem like it should help dry static BH time, it actually has some other consequences that mean it's not so straightforward. I'd generally suggest not hyperventilating much for a dry static (but if you can manage to do it lightly, and for not too long, while remaining very relaxed, then, yes, it can help increase times - especially when first starting BH practice).

There's also an argument that consistently trying to keep CO2 low at the start of and during (early part of) BH actually has the effect of leading your body to adapt towards that expectation - when you really should be doing the opposite to improve BH time by building up CO2 tolerance instead. (I don't know how true that is, but it seems as though it could be vaguely plausible, so make of it what you will...)

My overall feeling is that hyperventilation can help lead to longer times when you first start BH practice, and if you don't do it too much & too hard then it can help with feeling more relaxed for longer during BH since it takes longer for CO2 to build up. But the body might adapt to some degree as you practice it more, so it's probably not a good idea to continue to use it.

Anyway, I hope there's something helpful somewhere in all that!
CO2 tolerance is definitely a mix of both mental and physical aspects. It’s not just about chillin' and managing stress; your body does adapt over time with regular breath-hold practice. Those physiological changes, like buffering CO2, play a part too.
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