How to use it
No power breathing, hyperventilation or breath-hold games before or during cold water, a pool or the sea. It can cause a blackout with no warning. In cold water, breathe slowly, never go alone, and get out when shivering takes over.
How sure we are
C Evidence: contested. The research disagrees. Named, so you can stop worrying about it.
Sources
the physiology is well established. This is a safety rule, not a debate.
Not medical, legal or financial advice.