CO2 tolerance vs O2 efficiency - or how not to train for blackout?

[growingupninja]

After the mouthfill (and mask equalization) you're keeping the nose pinched all the way down or release the pinch after each equalization?

I EQ handsfree the whole way. The process is very much the same though once you start mouthfill and diving past RV, if you pinch your nose you have to release your nose between EQ, keep soft palate open and keep glotis closed so that you don't swallow the mouthfill and can still eq the mask. Basically what happens is the mask becomes part of mouthfill storage.

Remember that a high performance mask (Sphera or otherwise) is designed to compress, so to fully EQ the mask at depth you are probably putting in more air than you feel like you need to... doesn't really matter because you can sniff it back into your lungs on the way up, which for a 200' dive is noticeable, especially since I put it in when my lung air had normalish ppO2...

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[Penyu]

Apologies if I stole the thread but, I think improving DR does go directly to Penyu's question.

No worries there. Very interesting discussion anyhow. Despite all the great thoughts on the topic we are somehow still non the wiser. Training low O2 tolerance seems to be difficult and the how-to not quite established. Training CO2 tolerance is easy, but ultimately the route to trouble (potentially at least). At the same time its clear that top freedivers must apart from having more CO2 tolerance also a more efficient O2 consumption, because even if my low CO2 tolerance forces me to give up before blackout, I surely would blackout way before more advanced divers than me if I stayed on. Now there is still the possibility that a higher CO2 tolerance means greater relaxation in the absence of contractions and mental urge to breathe, therefore leading to lower O2 consumption, but my guess is that DR makes all the difference. I wonder about cardio fitness too though. I am currently the least fit I have ever been in my life (yes, there is a resolution coming up that will deal with this :- ), so I wonder if a better fitness state will make a big difference. Shame that diving doesn't get you fit and one needs to do something else to get there.

Cheers.

 

[Jaap]

You can train for low O2 fairly easily, if you are willing to train with an oximeter and push yourself to near blackout conditions. The only way to train low O2 tolerance is to stress the body in a low O2 condition. You may be able to figure out at what PaO2 you are at SAMBA and see a lowering of that threshold over time. Training the dive reflex is not training low O2 tolerance. The dive reflex causes O2 efficiency.

By training with an oximeter I know now that I get SAMBA around PaO2 = 38%, and that if I don't push it at all, the discomfort of a long breathhold will make me breathe well before that. Whether the number is correct I do not know because oximeters have low accuracy at low numbers, but it is at least consistent, so the interpretation stays the same.

The problem is, that this training and the awareness of your low O2 tolerance is not that applicable to dives, because there is no way to measure it and because the pressure change changes the way O2 and CO2 react with the body.