system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If the brain can only survive 4-6 minutes without oxygen, how can freedivers hold their breath for 8+ minutes?

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?
gpt
The level of oxygen in the body is dependent on two things - how much oxygen is in the bloodstream, and how fast it can be used by the body.
So in the case of David Blaine, he breathed pure oxygen for good period before his record attempt, and through practice increased the time that oxygen could last for by slowing down how much he uses that oxygen.

Free divers also are helped by the body slowing down in cold water their pulse rate, and how their body uses energy. These all slow down so free divers (after much practice) can hold their breath for longer than people on dry land.