How Long Can You Hold Your Breath?

Competitors float face down in a chilled pool, not to stop them cheating but to induce the mammalian diving reflex: when your face is submerged in cold water, outer blood vessels constrict, directing blood away from the extremities and towards the heart and brain. Your heart rate slows, reducing the rate at which oxygen is pumped around the body. With training, experienced breath-holders can drop their heart rate by twice that of non-divers upon immersion in cold water.

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