You won’t find The Barkley’s Marathons listed online in any of those Outside/Outside Times magazine compilations of the “world’s toughest ultramarathons.”

It isn’t held in the Moroccan desert, above the Arctic Circle or in Death Valley. There’s no “Canyon to Canyon” Grand Canyon hook, no Peruvian jungle to add exponential degrees of difficulty.

So take the organizers’ self-described “world’s toughest trail race” for what it is — hype. Rather like the name of the Tennessean who runs it, who goes by Lazarus Lake — real name, Gary Cantrell. “The truth is malleable,” he reminds us.

But what it lacks in ultra-marathoning community luster, the Barkleys makes up for in exclusivity and eccentricity — mainly Cantrell’s.

“The Barkley Marathons: The Race that Eats its Young” is a laugh-out-loud look at Cantrell’s 30 year old walk-hike-run through the mountains of Tennessee. It’s a running documentary about the annual five-lap race through the wilds of Frozen Head State Park, near Wartburg, Tennessee.

You might not see the world’s big names in the sport there on any given spring. The selection process for the 40 annual entrants leans towards committed, Type-A science and engineering types, with at least one “sacrificial lamb,” somebody they all know “has no business being out there,” running 20 miles laps through bracken and brier, in day and night, 12,000 feet up, and 12,000 feet down.

Runners have to figure out where to register, no mean feat. They have to pay the entry fee — arbitrarily set at $1.60, and “a white shirt,” or socks or whatever else the folksy Cantrell figures he’s in need of this particular year. And you need to bring him a license plate from whatever state or country you’re from.

The runners go up those mountains, down unmarked trails, trot through a creek-tunnel underneath a prison. And at various points, they have to locate a battered paperback book on an ironic subject or with an ironic title. Surely “The Naked and the Dead” has turned up among the vandalized literature.The runners are given numbers for each lap, each number is the corresponding page they must tear out of each waypoint book.

They have to cover 100 miles — actually, closer to 130 — in 60 hours, in the Tennessee spring. There’s little time for rest, little pause for recuperating or mending one’s ruined feet or brier-torn legs. Judgement fades, fatigue makes finding the waypoint books hard in daylight, impossible in the dark.

All they have to go by are their own maps, copied from this year’s trail course, and each other. No GPS.

And almost nobody ever finishes the damn thing — 14 finishers in 30 years. So yeah, it’s plenty tough.

Filmmakers Annika Iltis and Timothy James Kane capture the 2012 race in all its quirky glory — following runners (people with a LOT of training time on their hands) from California and South Carolina, Belgium and Germany as well.

But mainly, the camera’s on Cantrell and all the odd rituals and mythology attached to the race. It started as an “I could do better’n that” challenge to the James Earl Ray prison escape from Brushy Mountain Prison. Ray, who murdered Martin Luther King Jr., took days to find in the Tennessee wilderness. But he covered very few miles in that rough terrain.

The ultra-marathoners cover 15 times as far, every year. The ones who finish, anyway.

Cantrell piles on the colorful quirks. Those granted entry to the race “are sent a letter of condolences.” He announces the impromptu start time — day or night — by blowing a conch shell. He starts the race by lighting a cigarette.

If you quit, you are “tapped out.” A bugler plays “Taps.” The runners take this surprisingly well.

It’s all about the suffering, and good clean muddy fun — testing your body to its limits without having to travel to above the Arctic Circle for the 6633 Ultra, to Greece for the Spartathlon, or Morocco for the Marathon des Sables, the toughest of all.

The film could have used a little context (mentioning, by name, these better known races, for a start), outside experts to talk about its degree of difficulty. No, starting off with a quote about the truth being “malleable” doesn’t excuse you for swallowing the corny hype.

But “The Race that Eats its Young” is still a fun and quick introduction to a sport that, to most of us, seems so extreme as to invite the sort of eccentrics the filmmakers capture here.

MPAA Rating: unrated, with profanity, blood, smoking.

Cast: Gary Cantrell
Credits: Directed by Annika Iltis, Timothy James Kane. A FilmRise release. Running time: 1:29