I was watching Man vs. Wild on the Discovery channel last night. Bear was stranded on an island in the Pacific, spear fishing in some deep waters while swimming with sharks (no laser beams). He is already able to hold his breath for an amazing amount of time, especially if you consider the rigorous physical activity he is performing and the depth that he is swimming to. When he came to the top, he mentioned that every time he goes down he is able to hold his breath a little bit longer than last time. This seems counterintuitive to me - isn’t he using up more and more of the oxygen in his blood stream every time he goes down? Wouldn’t he need to take a decent break inbetween dives to really benefit from such a strategy?
I guess the underlying question here is, how long does it take you to reoxygenate after holding your breath on the order of a couple of minutes?
I’ve got no real answer for this, other than to suggest that maybe he’s stretching out his lungs a bit the first time, so that they can hold more the second time? Perhaps totally infeasible, but I know from playing a wind instrument that it takes a little while to warm up the muscles to be able to “fully” (I put that in quotes because geez, I can’t hold my breath for all that long) inhale. Maybe it’s the intercostal muscles or the diaphragm warming up?
I’d imagine that a part of it is psychological – learning to control that “you’ve got to breathe NOW” mechanism that kicks in when you’re underwater for too long.