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Physiology 10/12/2013

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Cold water swimming enthusiasts love the rush that comes with a near-freezing dip. Anda polar bear plunge does do lots of things to make you feel invigorated, says Christopher Tedeschi, an emergency physician at Columbia University Medical Center. But from your bodys perspective, a racing heart and gasping breath signal not so much excitement as self-preservation.

It doesnt even take near-freezing water to provoke a physiological response anything under 70 degrees Fahrenheit can be considered cold, according to Tedeschi. Hypothermia wont set in unless you plan on floating around for around an hour, but your body will still react very quickly to a sudden immersion.

What happens in the first one to two minutes is what we call the cold shock response, Tedeschi says. Your body reacts by getting very revved up.

The first and most immediate sign of this metabolic turbo-drive can be seen in the respiratory system. As soon as a person rushes or jumps into frigid water, he begins taking big gasps of breath. If a person cant get his breathing under control, he might start to hyperventilate within a minute or so.

In those first few minutes, your core body temperature wont change very much, but your surface temperature will start to drop. Your body reacts to this by constricting blood vessels near the skin. Constricting these blood vessels is a way for your body to try and conserve all the warmth that it can by bringing warm blood towards the heart and brain -- to do so, it has to cut down on the blood flowing at the periphery of your body. (You can see the opposite effect on summer days, when your blood vessels dilate, transferring heat from your core out towards the skin, dissipating heat and giving you a nice rosy flush.) This blood vessel constriction also affects your nerves, which might cause a pins-and-needles feeling or numbness.

This effect on nerves may also temporarily make it harder for you to make precise motions right after a freezing dip. Five minutes after being immersed in cold water, most people cant put a key in a lock, Tedeschi says.

While you might be tempted to prepare for a polar bear plunge by extending your New Years Eve drinking into the wee hours, you should probably resist the urge. Your body will thank you.

Being drunk for anything temperature-related is bad, Tedeschi says.

In addition to impairing a person's judgment, alcohol is whats called a vasodilator it opens up your blood vessels (hence people get flushed after having a few). So, the effects of being drunk are going to interfere with your body's efforts to constrict your blood vessels after you plunge into icy water. And while the feeling of vasoconstriction might be a bit painful, its a natural effort your bodys making to try and preserve your vital organs, even in the midst of your decidedly non-sober judgment. All in all, a drunk polar bear plunger might stay in longer than is healthier for him or her, and will probably lose heat faster.

So, being drunk is probably not the best condition to attempt a polar bear plunge. Being hungover probably isnt as bad, but a person recovering from a night of drinking will likely be dehydrated and metabolically not at their best, Tedeschi says.

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Polar Bear Plunge Physiology: What A Cold Water Dip On New Year's Day Does To Your Body