By the light of the full moon, Karnazes checked his watch -- 3:30 a.m. He finally realized what had happened. He'd fallen asleep while running and veered into the center of the highway. Shakily, he stood up.
Karnazes was near the end of the 2002 Providian Relay, a 199-mile footrace from Napa to Santa Cruz that's normally run by teams of 12 people. But as he had for the past seven years, Karnazes was running the entire course by himself, as what he wryly calls "Team Dean." When the horn jolted him awake, he'd been running for more than 50 hours, without sleep, and had covered 160 miles.
Brushing debris off his Polarfleece jacket and checking himself for cuts and scrapes, Karnazes set off again along the dark road. Only 39 miles to go, then there would be plenty of time for rest.
Karnazes is an ultrarunner. He belongs to a niche of long-distance runners who consider 26.2 miles -- the length of a marathon -- a mere warm-up. Their races, called ultramarathons, are generally between 30 and 150 miles long, often on steep hiking trails, lasting into the night, with no breaks for sleep. Just to complete them requires almost superhuman endurance. And even among ultrarunners, Karnazes is considered something of a machine.
At 41, Karnazes (rhymes with "Onassis") has a tanned body so taut that it looks like you could lob a tennis ball at any part of it, even his cheeks, and it would bounce back with a resounding thwack. It's a body that's taken him farther than anybody -- including him -- thought possible.
Last year, he placed second in arguably the toughest race in America -- the 135-mile Badwater Ultramarathon, held in Death Valley National Park in the middle of July, when temperatures soar to a flesh-frying 130 degrees. To insulate himself against ultraviolet rays, he ran in a protective suit made of synthetic Coolmax microfiber, keeping his feet on the road's white divider line to prevent the soles of his shoes from melting.
In 2002, Karnazes had gone to the opposite extreme, flying to Antarctica and becoming the first person to ever run a marathon to the South Pole.
Karnazes balances all these achievements with a wife, two kids, and a full-time job -- he and a business partner are starting a healthy snack foods company. They recently put the finishing touches on what they hope will be the crown jewel of their product line: a low-carb, fat-free "Cheetos-type product." To fit it all in, Karnazes sleeps only four to six hours a night.
"Dean," I ask during an interview, "are you human?"
"I'm human," he says. "I have every other weakness that every other human has, if not more. It's just, I push myself to the level that I've broken down some mental barriers about what a human can do, physically."
Long-distance running is probably as old as the human race. The ancient Greeks ran footraces of various distances and created the marathon. It's based on the journey of a messenger who is said to have run 26.2 miles, to Athens from the city of Marathon, to deliver news of a battle. He reputedly dropped dead afterward.
Long runs were also popular with Native Americans, both as sport and as a means of communicating between villages. After all, you don't need any high-tech equipment and, with regular practice, more people than you'd think can become capable of jogging great distances. To this day the Tarahumara Indians of Mexico's Copper Canyon region run up to 100 miles at a time on mountain paths. They wear sandals made of old tires and their diet -- unlike the abstemious regimens of modern Western athletes -- consists mostly of corn and copious amounts of strong homemade corn liquor called tesguino.
Multiday walking and running races became a fad in Victorian England. They were eclipsed in popularity by the marathon, introduced in 1896 during the modern revival of the Olympic Games in Athens. In 1921, a now well-attended 50-mile road race called the Comrades Marathon was launched between the South African cities of Durban and Pietermartizburg.
But it wasn't until 1974, when Gordon Ainsleigh's horse fell ill before an annual 100-mile equestrian race in California's Sierra Nevada mountains, that ultrarunning took off as a sport. While his opponents rode, Ainsleigh, an American, ran on foot from Squaw Valley to the town of Auburn. He followed a treacherous route that wove among snowy mountain peaks and through hot box canyons, giving birth to what's known today as the Western States Endurance Run.
The Western States was the first trail footrace of great distance, and it sparked a movement that has steadily grown in popularity. Today, there are ultramarathons all over the world -- from Marin County to Mongolia -- and hundreds of thousands of participants of all ages, both women and men. Karnazes has run the Western States eight times; his best finish was fourth place last year.
JoAnn Dahlkoetter, a Stanford sports psychologist and author of Your Performing Edge, says those attracted to ultras are often loners who don't accept other people's views on the limits of human endurance. "They see body aches and pains -- adversity -- as a way to explore their inner potential," she says. "It can almost be like a Zen kind of thing or a trance -- being out there doing something repetitive for long periods of time."
A runner's biochemistry changes in dramatic ways as he runs longer and longer distances. The body is forced to consume fuel and oxygen much more efficiently. A well-trained endurance runner has much stronger heart muscles and a heart rate about 43 percent lower than a sedentary person's. A runner's cardiac output -- the volume of blood pushed through his circulatory system -- jumps by 75 percent, delivering more oxygen to his muscles. Due to an expansion of cellular energy producers called mitochondria, the amount of oxygen absorbed into his tissues rises by up to 50 percent. Distance runners also shed a larger proportion of body fat, making them more able to pound their feet against the pavement for long periods without damaging their joints.