Surviving Extreme Physical Challenges

Your body's first reaction to hitting icy water isn't to swim; it's a gasp that can make

you drown instantly. This is the cold shock response. But that’s just one extreme your

body handles. If you’re a freediver, the deep-sea pressure can shrink your lungs to the size

of a fist. For elite cyclists, fatigue is different for a 45-second sprint versus a

40km race. And get this, being super fit has a downside: your immune system

crashes right after a hard workout, making you an easy target for germs. It’s all about how

we survive at the limit.