i was sort of taught to hyperventilate at the freediving course i attended, only 5 breaths right before the dive though. this thread on spearboard just came up about a week ag with a lot of really good info about hyperventilation. the reason i was taught to do it was to increase your ratio of O2 to CO2, but another diver argued that doing a full exhale right before you dive will get all the CO2 out, keep your heart rate down, and is safer. apparently hyperventilating makes you think you can stay down longer, it tricks your body into thinking it doesn't need air or that it doesn't hurt as much, when it really doesn't increase your bottom time.
i havn't tried the long exhale method, and i've never had any issues with the 5 quick breaths before i dive...but the info on this thread makes sense so i'm going to give it a shot next time i go out
How Much Deeper Can i Dive With freediving fins and proper gear? - Spearboard.com - The World's Largest Spearfishing Diving Social Media Forum
I was a little confused in your post since it seems to imply that you should dive with empty lungs, and immediately thought how is this possible? So I followed your link, and found this:
Final Breaths…
Breath for approximately 2 minutes, from the belly, all the time focusing on the exhale.
Keep these breaths relaxed and no deeper than you may do so whilst relaxing in a ‘normal’ situation.
You are looking at ensuring that the exhale is approximately 2x the length of the inhale. These are not deep breaths, they are simply controlled.
Start you final breath phase.
Take a slightly deeper breath in.
Breathe EVERYTHING out… And i mean everything, until you are having to spit out the last bits of air in your lungs.
Your final breath in needs to be focused and almost mechanical in its nature.
Start breathing in from the diaphragm. Keep breathing in from the belly until you can’t get any more air in.
Shift your focus to breathing in from the chest… keep breathing in until you cant get more air in to the chest.
Shift you focus finally in to breathing in to the collar and neck… This is a bit abstract I know but it really finalises the breath and ensures you are holding a good posture for maximizing your capacity.
OK…. Now its time to dive.
It seems that the technique also includes instructions for the final inhale before diving. It think I may take these instructions to the pool next time and test it out against hyperventilating.