Picture for a moment, walking into an ice-cold lake. Your feet are ground zero for the shock wave that goes through your body, and your brain tells you to get the hell out of there. But in you go anyway, because you’re doing a polar plunge.
These acts of wintertime daredevilry are gaining in popularity. Some strip down to celebrate the New Year, or to raise money for charity, like Plungefest in Annapolis, Maryland, where people including Adam Hays, a Special Olympics athlete, are deemed Super Plungers, for going in every hour for an entire day.
And interesting things happen when your body goes into a cold-shock response, according to John W. Castellani, a research physiologist in the Thermal and Mountain Medicine Division at the U.S. Army Research Institute of Environmental Medicine, starting with your feet freezing and your heart pounding out of your chest. And there’s more.
The shock triggers activity in your sympathetic nervous system (fight-or-flight response), prompting a dump of hormones like adrenaline and noradrenaline into your system, Castellani says. That’s where the thrill comes in.
Take a Deep Breath
In the moments after registering the temps, an uncontrollable reflex results in a big gulp of air. So instead of jumping in, walk or run, says JohnEric Smith, an exercise physiologist at Mississippi State University. Enter to shoulder height, take a huge breath, go under—then get outta there.
Cold to the Core
Hit the water and the body goes to DEFCON 1: survival mode. It redistributes blood from the extremities and concentrates it around essential organs (heart and lungs). It’s also the body’s way of conserving heat.
Heat escapes two to four times faster in water than in air, but it takes a few minutes for your core temp to drop. Since polar plunges take a minute or less, you’re unlikely to lose motor function.
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