Now in its eighth season, American Ninja Warrior continues to challenge elite athletes with obstacle courses unlike any other—to the point that only two of the show’s competitors has ever successfully achieved "Total Victory" (both in season seven). Here are a few things you might not know about the series. May the best ninja warrior win.

1. THE SHOW DOESN’T HOLD CASTING CALLS.

Unlike other competition shows, American Ninja Warrior doesn’t hold traditional casting calls. Prospective contestants can send in a submission tape, then producers choose around 100 people to “run” in each of the cities they are visiting. If your tape doesn't get you one of those handpicked spots, there’s always a walk-on line. But you’ll need a different type of training for that. “The walk-on line is like waiting for Black Friday sales,” producer Brian Richardson told mental_floss. “You sleep in a tent for a week or more outside the course, with no guarantees. We usually only have time to run 20 to 30 people from the walk-on line. Sometimes people spend a week camping out and never get to run the course.”

2. THE COURSE IS EVEN MORE INTIMIDATING IN PERSON.

Richardson admits competitors are caught off-guard by how complicated the obstacles are when trying to run them in the flesh, as opposed to from the safety of their couch. “For most of our competitors, they've practiced on similar looking obstacles at home or at their gym,” he says. “But when they step up to compete—under the lights, in front of a crowd, with a camera in their face—it's a lot more intimidating.”

3. SMALL CHANGES CAN MAKE A BIG DIFFERENCE IN A COURSE.

While some of the obstacles on American Ninja Warrior come directly from Sasuke, the Japanese program upon which it is based, others are totally original to the stateside series and aren’t created overnight. “We work with the company that builds our obstacles, ATS, and brainstorm for months on ideas to test strength, balance, and agility,” explains Richardson. “It might start as a drawing on a napkin. Then we'll build a prototype and test it in the ATS warehouse. Ultimately, if it passes all the tests, then we will make it part of our course. Even when it's built on the course, we test it with athletes dozens and dozens of times to dial in the difficulty. Moving a rope six inches closer or farther away can make a world of difference.”

4. CERTAIN BODY TYPES MAY HAVE A COMPETITIVE ADVANTAGE.

Given the show’s title, you’d expect the competitors most likely to complete each course would be the big muscle guys with out-of-this-world strength, but that’s not always the case. “Typically, in most of the American sports, size and strength are a big advantage,” says American Ninja Warrior co-host Matt Iseman. “What we've seen in this, it's really strength‑to‑weight ratio. So the less weight you have to carry on the course, the better your strength does on that. I think we saw that last year with the biggest story, Kacy Catanzaro, who is five-feet tall [and] less than 100 pounds. No one thought she was strong enough, but the reality is she was so light—and she is incredibly strong—that she didn't have all this mass.”

5. NFL PLAYERS WANT IN ON THE ACTION.

Whether the leanest contestants have a competitive edge or not, co-host and former NFL player Akbar Gbajabiamila says pro football players often contact him to get on the course. “I get guys like NFL star quarterbacks, Aaron Rodgers from the Green Bay Packers, telling me, ‘I love this show,’” he says. “I get guys like Charles Woodson texting me, like, ‘Man, this is amazing.’ Other guys texting me or tweeting me, saying, ‘Look, give me your number. I want to get on this obstacle course because I think I could do it.’”

6. NOT ALL COMPETITORS HAVE A CLEAN BILL OF HEALTH.

Since the start of the show, American Ninja Warrior has run some pretty inspiring competitors through their courses, like those suffering from rheumatoid arthritis or diabetes, and even recent open-heart surgery patients. “You don't have an excuse when you see how hard some of these competitors work and the adversity that they overcome,” says Iseman.

7. STAGE 4 WAS THE TOUGHEST OBSTACLE TO BUILD.

When asked about which obstacle was the toughest to build, Richardson says it's probably "Stage 4 in Las Vegas. It's four stories high, and with the way the desert winds blow in Vegas, it can be scary to be up at the top."

8. PRODUCERS ARE CHALLENGED BY THE NINJAS THEMSELVES.

Given that the show's producers are dealing with people who consider themselves ninja warriors, these contestants are stealthy, recreating obstacles at home to figure out the best way to work the course. Which means that producers must always remain one step ahead of their competitors. “Our best athletes train year-round for ANW now,” says Richardson. “There are gyms devoted to Ninja training that are popping up all over the country, so people have a lot more access to obstacles like the Warped Wall. We want to test them every year, so we have to keep creating obstacles that are fun, and challenging, and entertaining to watch at home.”

9. VIDEO SUBMISSIONS HAVE INCREASED 50-FOLD SINCE THE SHOW'S DEBUT.

In its first season, producers received tapes from 1000 American Ninja Warrior hopefuls. Last year, producers were slammed with approximately 50,000 videos of folks vying for a spot on the show.