North Vancouver runner Gary Robbins is in Tennessee to attempt, once again, one of the most difficult physical challenges known to humankind — the "100 mile" Barkley Marathons.

The foot race, held annually in the backwoods of Frozen Head State Park, has a quirky culture and 30-year history of defeating the vast majority of participants.

Nobody even completed the course until the 10th year the race was held, and many years see nobody cross the finish line.

Robbins came close in his first try last year but eventually got lost.

Runners have 60 hours to complete the race, and many push for the partial completion goal of three 20-mile circuits, called a "fun run."

"The whole idea of Barkley is that it's a true physical and mental test," said Annika Iltis, co-director of the documentary film The Barkley Marathons: The Race That Eats Its Young​.

"People's bodies get ripped up, you know … the feet maceration," said Iltis. "You see them come back and their bodies definitely look defeated, but it's hand-in-hand with the mental aspect of it."

The race goes through two nights, and the route changes each year, making the distance actually longer than 100 miles, though the exact length isn't known.

Race preparation

Robbins has been keeping up an extensive training regimen but slowed down in the last week in anticipation of the event.

In a video posted online on March 20, Robbins gave an update on his progress.

"Things are tight and sore. Neck and back and shoulders are quite sore from running with an eight to 10 pound backpack on," he said. "I'm very happy with where we're at right now."

In the month leading up to that video, Robbins reported on his blog that he completed a total of:

129,000 feet (39,319 metres) of climbing

187 miles (301 kilometres) running

72 hours of training

He posted a photo on Instagram on Wednesday including the caption, "No matter what happens, in one week I'll surely have some sweet hallucination stories to share. HERE WE GO! WEEEEE!!"

2016 Barkley Marathons attempt

Last year, about a month after attempting the race, Robbins reported that he still couldn't feel his toes.

In an interview with CBC's As It Happens, Robbins told host Laura Lynch that during the run he'd been hallucinating and wasn't able to think rationally, making it impossible to navigate with a map and compass (the route isn't marked).

"I ended up getting lost. I lost about two-and-a-half hours of time just kind of going in circles in the forest. And I timed-out on that 60-hour cutoff," he said at the time.

Gary Robbins listens to race instructions before the start of the event in 2016. (Keith Knipling)

"I don't have a death wish, but I definitely really appreciate being pulled to my outer limits and having to face things front on and really discovering a side of myself that you're just never going to see in day-to-day living," said Robbins.

Race start time unknown

Race organizers don't release a list of people who have been sent a "letter of condolence" letting them know they're invited to take part.

Racers themselves don't know exactly when the race will start — it could be any time of the day or night. A conch is sounded one hour before the race begins to let the runners know. The race itself begins when the organizer lights a cigarette.

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