MIAMI — Imagine running to the South Pole in a marathon where the temperatures plummet to 42 below zero, and the only way you can breathe without freezing your trachea is with a Neoprene rubber muffler covering your mouth and nose.
Now, imagine racing 135 miles through three mountain ranges and California's "Death Valley" desert in temperatures that soar to 130, so hot that if you run part of the course on the road's asphalt instead of the white line your shoes could start melting.
How about running 50 marathons in 50 states in 50 days, ending in the New York City Marathon?
Dean Karnazes, among the world's most famous endurance runners, has done all of the above — and a lot more. He was in Miami recently to take part in the Fitbit Miami Marathon.
"I've never run Miami," Karnazes, 55, told the Miami Herald ahead of the race. "I'm so looking forward to it. Every marathon has a certain feel, almost like its own culture. I've heard that the Miami Marathon has a really big Latin influence and is a really fun event.
"It's a scenic course, and you don't have something in Miami that we have here in San Francisco. They're called hills. It's a very approachable course, Miami."
"Approachable" to Karnazes might be running through only half the United States instead of the Los Angeles to New York City race — 3,000 miles — he did in 75 days in 2011.
Or "approachable" might be running a marathon "before breakfast" to train for his ultra races. "When I'm training for a big ultramarathon," he said of his races longer than the conventional marathon distance, I get up early, like 3:30 or 4 a.m., run a marathon and then do high-intensity interval training during the day. I never sit down. I do all my writing and interviews standing up, and do speed work in the afternoon."
At least 10 times he has run a 200-mile relay race solo against teams of 12.
And in 2005 he ran 350 miles "in 81 hours, 44 minutes," stopping only to change his clothes and "go — quote, unquote — big potty. ... What happens is you kind of fall asleep while you're running," he said, "but your body keeps moving along."
Karnazes, an author and inspirational speaker who is sponsored by the North Face and is a longtime ambassador for title-sponsor Fitbit, considers most marathons more like social events than completely competitive endeavors.
His next ultramarathon is a 50-miler in April. Karnazes, who has written four books, including the New York Times best-selling "Ultramarathon Man, Confessions of an All-Night Runner," said he typically does 20 marathons a year and maybe 10 or 15 ultras. In total: about 5,000 miles annually and around 100,000 miles since he decided, on a whim, to run 30 miles on his 30th birthday.
But his running career actually began when he was in kindergarten, he said, racing home while his mom was taking care of his baby sister.
Karnazes, 5-9 and 148 pounds, does lots of cross training to build his muscles and is blessed with exceptional biomechanics. He sleeps four to five hours a night and eats a diet that is "basically a hybrid between a Paleo, Mediterranean and raw diet."
"If you can't pick it from a tree, dig it from the earth or catch it with your hands, I don't eat it," he said. "I don't eat anything in a bag. I don't eat anything processed. No bread, no pasta, no rice, no oats."
He does eat plenty of fresh fish and seafood, and occasionally meat and chicken, his wife Julie said.
"I've been pretty much analyzed as far as how I'm able to run for so long and why I don't get injured," Karnazes said. "My alignment is good for running. I've lost toenails, which have been the extent of my injuries. I think it's largely hereditary and has to do with my cross training and conditioning my entire body for the rigors of running."
The father of a 23-year-old daughter and 20-year-old son, Karnazes, who was the valedictorian at California Polytechnic State University in San Luis Obispo and has his master's in business administration from the University of San Francisco, is married to high school sweetheart Julie, who said she walks long distances to keep in shape.
"He's a very focused individual, and a very kind individual," Julie said of her husband, who has a foundation — Karno Kids — "where his focus is making certain children get up and get outside. He has been very generous, with donations that come in, to various venues."
Julie said that her husband "is gone a lot but has taken us as family members to some of the most lovely places he has run."
The South Pole in 2002 wasn't one of them.
"It was supposed to be the inaugural South Pole Marathon," Karnazes said. "They told me there would be 40 or 50 runners there. I get to Antarctica and there were six people. Three of them left right away.
"We kind of got stuck on the most remote place on Earth that was supposedly a marathon distance from the South Pole. But it was actually more like 28 miles away. It was like a comedy of errors and amazing we didn't die."
His time? "Over nine hours," he said.
Do you think people consider him a little wacky? Julie was asked.
"Yes, yes I do," she said. "I hear that a lot when we're together. People say, 'Wait. I don't understand.' "
When does Karnazes figure he'll stop doing this crazy stuff?
"I always tell people, 'My finish line is a pine box,' " he said.