And what about people like David Blaine or Tom Sietas? Sietas held his breath underwater for over 22 minutes (world record). I know they train for it like months and even years, but doesn’t holding your breath = no oxygen to brain?
Permanent brain damage apparently occurs just after 4 minutes of lack of oxygen to the brain, so why are freedivers left generally unscathed after 8 or 10 minutes without air?
In: Biology
I really feel like I haven’t seen the real ELI5 answer yet.
It’s because “holding your breath” *doesn’t mean* “no oxygen to your brain.”
Inside your body, oxygen is carried by your blood to all of your different parts. Then, the blood (with some of the oxygen used up) is sent back to your lungs to get more oxygen. But, even if there is no new oxygen in your lungs, you still have a decent reserve of oxygen in your blood for your parts (including your brain) to use up. The only way to *immediately* get to “no oxygen to the brain” is decapitation. Otherwise, as long as your heart is beating (and *all* of the oxygen in your blood hasn’t been used up), your brain will continue to get oxygen.
What freedivers and David Blaine can do is various methods of (1) increasing the amount of oxygen that their blood can carry and (2) decrease the speed at which their body uses that oxygen. So, when they go underwater, they can last longer on the oxygen already stored in their blood until they need to take a breath.
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