On Sunday, Jimmy Fallon will dive into the cold waters of Lake Michigan to raise money for the Special Olympics, joining Mayor Rahm Emanuel and thousands of others in Chicago for the annual Polar Plunge event.
Mayor Emanuel challenged the late night comedian to enter the winter event in exchange for an interview on Fallon's new gig, The Tonight Show. Fallon accepted the mayor's dare and confirmed his attendance on Twitter with hashtag #SwimmyFallon.
Fallon was less enthusiastic when he learned how cold Lake Michigan is. According to Michigan State University, the water temperatures in Chicago were around 36.5°F (2.5°C) on February 23, as frigid as the ice-cold waters of the Bering Sea.
"It sounds like a nightmare," Fallon said during The Tonight Show on February 26. "It's freezing in Chicago right now."
What should Fallon expect and how can he prepare for the plunge? National Geographic turned to Arctic swimmer Lewis Pugh for guidance.
A cold-water swimming champion for more than 27 years, Pugh knows a trick or two about surviving polar plunges. He was the first person to swim across the North Pole in 2007 to bring attention to melting sea ice in the Arctic Sea. He swam in below freezing water temperatures of 28.9°F (1.7°C) for 18 minutes and 50 seconds.
How long Chicago's polar plungers stay in the water is up to them. Here's Pugh's advice for Fallon.
Take a Cold Shower
Don't be shocked by the cold water; prepare for it. According to Pugh, Fallon should start a regimen of cold showers to acclimatize. He recommends two cold showers today for two minutes, and one on Saturday for five minutes.
"This will start preparing him mentally. The body can acclimatize quickly. It's like studying for an exam," said Pugh. "You can do a lot in the last few days."
Uncomfortable? Certainly. But studies show that athletes regularly exposed to cold water have a delayed onset of shivering and a reduced response to the cold. Pugh also recommends that Fallon avoid saunas, jacuzzis, or dieting before Sunday.
Get in Quickly
Don't stand around too long on the lake's edge, Pugh cautions. Fallon should jump in as quickly as he can. He'll want to start his plunge with his highest core body temperature; Chicago's cold weather could bring down his temperature before he even hits the water.
According to Johns Hopkins Medicine, average body temperature—which varies depending on gender, age, and individual rate of metabolism—ranges from 97.8°F (36.5°C) to 99°F (37.2°C).
But Pugh's core body temperature has been recorded as high as 101.3°F (38.5°C) before embarking on a cold-water swim. This unusual ability to raise his temperature in anticipation of entering freezing water is an anomaly that's been documented in other Arctic swimmers.
Even with that increase, Pugh's body temperature dropped to 95°F (35°C) when he swam in the Arctic. "I knew that [18 minutes] was my maximum. Another minute and I might've lost my fingers."
When Fallon takes the dive into cold water he'll feel like he can't breath, says Pugh. That's a natural reaction called cold-shock response.
"There's a misconception that the passengers of the Titanic died of hypothermia,” said Pugh. "But they drowned. You gasp in water and drown. So don't panic. Just breathe!"
Hypothermia sets in when core temperature dips below 96.8°F (36°C) because the body's metabolism can no longer generate enough heat to counterbalance the cold.
The initial cold-shock response will pump adrenaline into the body, increasing the heart rate and blood pressure, but that will eventually fade away.
Get Out Within 3 Minutes
Pugh spent seven summers living in the Arctic before making his swim across the North Pole. Though he braved the cold water for nearly 19 minutes, he recommends a much shorter swim for inexperienced swimmers. That's because water is an excellent conductor of heat, so it wicks warmth away from the body much more rapidly than cold air.
"Anything under two or three minutes will be fine," said Pugh. "But don't swim far out."
Put on Some Clothes
Once he's taken the plunge, Fallon should get dressed quickly. Wet clothing loses its ability to insulate from the cold so core body temperature could plummet, raising the risk of hypothermia.
"Don't mess around wet in a cold wind," said Pugh. "Get dressed and then get a good cup of hot chocolate."
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