[FrustratedMonky]

So just curious. You do want to have the CO2 levels, so you get the trigger to breath? But to free dive don't you want to stay down longer? So is the method more about dealing with the urges? Mental ways to understand the urge to breath, but be able to block it?

[aqme28]

There are two gases that need to be exchanged when you breathe. You need to get rid of CO2 and you need to get O2. When you hyperventilate, you purge CO2, but don't really change your O2 content.

This matters only because CO2 is what triggers your desire to breathe, but O2 is what causes you to actually pass out or not. So what happens is that you might pass out before you realize you need to come up for air.

[Azrael3000]

Correct. You can deal with the urge to breathe with your brain. High co2 has additional benefits for your metabolism, you just need to deal with it. If that sounds interesting take a free diving course its a great way to learn more about this fascinating sport.