Forty-seven thousand human beings will run the New York City Marathon on Sunday, Nov. 6. If the race were one huge relay, the runners would circle around the Earth more than 51 times. What drives marathoners to run such lengths?

The desire to win surely motivates an elite few to crouch at the starting line; others behind them may be there for the love of running, philanthropy or sportsmanship. But when the starting gun fires, regardless of each runner's reason for racing, every one of them knows their willpower is about to be tested.

The marathon is a universally accepted yardstick of willpower, and for good reason. Anyone who finishes a marathon is worthy of respect. But on the 26.2-mile course, very occasionally, some people find hidden depths of inner strength that seem to defy explanation.

Here are five stories of the greatest marathon-related feats. These racers didn't all win – in fact, one came in dead last. But their stories exemplify the true purpose of a marathon: the triumph of the human mind over its physical circumstances.

Oldest Runner

In October, Fauja Singh came in last at the Toronto Waterfront Marathon. A typical marathoner might take four hours; the fastest come in closer to two. It took Singh more than eight hours to complete the race — he is 100 years old.

Dressed in bright yellow, with a matching turban and with a chest-length white beard, Singh reportedly told his coach as he turned the final corner of the course that "achieving this will be like getting married again."

Singh ran his first marathon at age 89, and set several age-related records in the seven marathons he ran since then. Despite the fact that Singh has provided numerous proofs of his age, including a passport, to Guinness World Records, that organization has yet to recognize any of his marathon records because he hasn't been able to provide a birth certificate.

Most Inspirational Comeback

Any disease can make the already difficult task of running a marathon nearly impossible. But multiple sclerosis, which sabotages the normal functioning of nerves and muscles, is a strong candidate for the disease least compatible with marathoning.

And this makes Patrick Finney's accomplishment all the more incredible.

On New Year's Day 1998, the Texas software engineer awoke with numbness in his legs. Doctors diagnosed him with multiple sclerosis. By 2004, he was unable to walk.

But with the help of medications and physical therapy, he retrained himself to balance while standing, and then to put one foot in front of the other. He did it faster and faster, and then he started to run. And he kept running.

"The first year was a real struggle for me," he was quoted as saying. "I was going through a pair of running shoes every two weeks, because I was scraping them up as I dragged my feet."

This September in Washington, the 48-year-old finished his 50th marathon in 50 different states, the first person with multiple sclerosis to do so. "It's been a wonderful experience," he told reporters.

Coldest "Marathon"

The coldest "marathon" of all time was actually a half marathon. Some purists might object to a half marathon being on this list. They shouldn't.

The Siberia Ice Marathon takes place in Omsk, Siberia (where the writer Fyodor Dostoyevsky was infamously exiled). During the race, organizers hand out hot tea instead of water, and according to officials, everyone goes home with a complimentary "warm cap."

During the coldest of these races, held in January 2001, the air temperature averaged minus 39 degrees Fahrenheit, and it got as low as minus 44. Of the 134 people who started the race, 11 finished.

To put that day in perspective, anyone who started that race only had an 8 percent chance of finishing it, about as low as the current freshman acceptance rate at Harvard University.

Most consecutive marathons

On Jan. 18, 2010, Stefaan Engels hurt his foot. He'd run a full marathon daily since January 1 of that year, and had planned to continue to do so. For a few days, he tried riding a hand-powered tricycle instead, but he decided it didn't really count towards consecutive marathons. So he rested, and eighteen days after his injury, he started over.

Then, he ran a marathon every day, for 365 days straight.

The key to his endurance, he told reporters, was running slowly — he typically took four hours to run a marathon, rarely finishing in under three.

He concluded his torturous year this past winter at age 49, shattering the previous record of 52 consecutive marathons, held by Akinori Kusuda, who achieved his feat at age 65.

During his marathon year, Engels ran almost 10,000 miles, and went through 25 pairs of shoes.

Ultimate display of willpower

If there's one person who in one race broke through the ceiling of human determination, it's Uta Pippig.

In 1996, while running in the 100th anniversary race of the Boston Marathon, Pippig was suffering from intense menstrual cramps, menstrual bleeding and violent diarrhea.

But the blood and feces running down her legs weren't her primary concern as she crested Heartbreak Hill, a well known and aptly named feature of the Boston course. It was her competition, Kenyan speedster Tegla Loroupe, nearly 250 yards (222 meters) ahead — a huge gap to overcome so late in the race.

Over the remaining five miles, television cameras rolled and flashbulbs popped all around her. People on the sidelines may have gasped, but if they did, Pippig ignored them. Perhaps the word "willpower" doesn't even describe the force that drove her to the finish line through brutal pain and nightmarish indignities.

But she didn't only succeed in overcoming her circumstances. She also overcame her opponent, claiming her third straight Boston marathon victory with a huge smile on her face.

This story was provided by MyHealthNewsDaily , a sister site to LiveScience. Follow MyHealthNewsDaily on Twitter @MyHealth_MHND.