How much hypoxia does it take to cause (lasting) brain damage? Do long-term freedivers run into problems, like old boxers and American footballers? I’ve always been leery of any sort of intense breathing exercise because of this concern.
Certainly not in any obvious way like people that suffer repeated blows to the head. There’s some debate over whether loss of motor control (they call it “samba” because it’s kinda like you start dancing involuntarily) can cause damage that makes it more likely to happen again in the future, but I haven’t been able to find any evidence that there is any damage at all in normal training and even the former seems to be controversial.