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Courtney Dauwalter had run 88 miles through the ColoradoA state in the west of the US that contains much of the Rocky Mountains. mountains when her eyesight began to fail. "I couldn't see my hand in front of my face," she remembers, "but I could still see my toes."

With 12 miles of the race left, she decided to carry on.

Soon she was 90% blind - but still she did not give up. With another runner beside her describing the ground ahead, she finished the race. Fortunately her sight soon came back.

A marathon is 26 miles 385 yards long. An ultramarathon is any race longer than that. Last year Courtney became the first person to win three of the world's toughest 100-mile races in a single summer.

She had not run further than 10km until one day she decided to enter a marathon. To her surprise, she made it to the finish line. She moved on to a 50km race and then a 50-mile one.

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In 2012 she made her first attempt at 100 miles, but had to drop out. Then, she told herself that she could do whatever other runners did. Two years later she had her first 100-mile victory.

"My process is just to start repeating a positive mantraA phrase that is often repeated, like a motto. The word comes from a Sanskrit term referring to a sacred utterance. to myself," she says. "'You're fine. This is fine. Everything is fine.'"

Is success all in the mind?

Yes! Courtney would never have finished all her races without her positive mind. Her ability to carry on in moments of crisis are what sets her apart from other runners.

No! Having a positive mindset is important of course! But you need to be very, very fit to take part in an ultramarathon. Most people will naturally never be able to run that far.