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Comment by sriram_malhar | Hacker News Reader

Incredible!

Assuming I understand such a feat even with exposure to pure O2, how does he manage to avoid CO2 build-up? Or, how did he train to retain CO2?

Cells use up O2 and release CO2 into the blood to form carbonic acid (keeping it simple), so the blood pH levels drop, which the body does not care about at all. This is what induces the suffocation reflex.

I wish I had known this while trying to master breathing while swimming freestyle: it is not just their VO2 max, but also their ability to retain CO2. Both aspects need to be trained.

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The body doesn't notice a lack of oxygen. Hence the danger of carbon monoxide poisoning or air without o2 etc, as you won't notice o2 lacking. What you notice is co2 buildup, and as long as you keep breathing that's not happening.

When freediving, you can't really avoid it. What you learn however is how to deal with it. Control your diaphragm when it wants to start breathing, as the spasms are wasted energy. It's mostly a mind thing. With simple exercises (co2 tables) and just getting used to the feeling, it took my quite a short time to reach 5 minutes.

One "trick" btw is hyper ventilating. But DONT DO IT! It get rids of lots of co2 in your blood stream / lungs, so it takes a bit longer for the co2 buildup. But you need that buildup. Even though it's painful, that's your only signal as to how you're doing and which you kinda calibrate against. Especially when diving, hyper ventilating before can make it so you suddenly go unconscious before you felt the urge to surface.

Wow, TIL hyperventilating increases the danger! My brothers and I used to compete against each other in swimming pools, and we'd always hyperventilate at the beginning, thinking this 'got the oxygen in'. In any case, it definitely helped. Glad we never got into trouble this way.

My personal record is ~3:30, but I'm pretty sure I could go well past that if we had practiced instead of just competing.

You can still do it, just never do it alone

We used to hyperventilate before underwater training to extent our time under water

Actually knew someone who didn't make it, after (presumably) using the hyperventilation technique. Such a senseless way to go.

You cant avoid co2 build-up, you can only slow it down, main factor here is relaxation. Particularly your brain needs loads of o2, so if you can keep that calm it helps a lot. Obviously a slow metabolism helps as well, so before big static performances fasting is common.

And regarding co2 tolerance, it is a training effect. With training you can withstand much higher levels of co2 without resulting in panic

And co2 build up isn't even that dangerous, just really uncomfortable. Lack of co2 (from hyperventilating) actually inhibits oxygen uptake and causes dizzyness (up to passing out) that way

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