Stephen King made crucial demand for his new movie as fans forced to watch on treadmills

Stephen King made one major change to The Long Walk's script as the acclaimed author's first-ever book has been adapted for the silver screen.

The acclaimed author needs no introduction; from Carrie and It to The Outsider and The Institute, you've likely seen numerous of his TV and movie adaptations over the years. And now, the first novel King wrote, The Long Walk, is being released in theatres this September.

King penned the novel as a college freshman under the pseudonym Richard Bachman, some eight years before his first published book, Carrie, was released in 1974.

The Long Walk is set in a dystopian version of the US, where a totalitarian regime governs all 50 states.

Each year, 100 teenage boys are selected to participate in a brutal contest. They must keep a steady pace of at least three miles per hour for the longest time.

After three warnings, they are 'ticketed' - in other words, brutally executed on the spot by armed soldiers.

The gruelling journey continues until only one boy remains. He wins 'The Prize' - basically, anything he desires for the rest of his life.

Directed by The Hunger Games' and I Am Legend's Francis Lawrence, the movie stars Mark Hamill, Cooper Hoffman, David Jonsson and Garrett Wareing.

In an interview with ScreenRant, producer Roy Lee lifted the lid on the only note King gave after reading the script.

In King's original book, the boys had to exceed speeds of four miles per hour. However, it turns out that he had a change of heart.

Lee said: "[King's] like, 'Can you change it from four miles per hour to three?' Because that's what was written in the book. He goes, 'There's no way that you could walk four miles an hour for that long'."

He added: "That was the only initial note when he gave back. The ending was what it is, and he was like, 'I love it. But I think you need to reduce the speed.'"

Pretty reasonable from the 'King of Horror,' don't you think?

Ahead of its release, theatregoers were put to the ultimate endurance test in an immersive screening experience.

At the exclusive event, participants had to match the characters' gruelling pace - walking on a treadmill at three miles per hour for the entire 108-minute runtime. Fall behind, and you risk being ejected from the theatre.

Horror movie expert Josh Levesque was among those invited and documented the challenge on TikTok. While he says he 'crushed it,' thanks to the encouragement of fellow horror fans cheering each other on, not everyone managed to cross the finish line.

In the comments, he revealed only two theatregoers failed to make it to the end of the movie. One tripped up - literally - with just five minutes left to spare.

Other social media users loved the treadmill concept.

"Maybe 'movie gyms' would actually motivate me to get in shape," one person said, as a second wrote: "What a wild idea, love it!"

A third said: "I've watched horror movies while on the treadmill. It's actually surprisingly easy to zone out and forget you're walking."

Do you reckon you could survive it?

The Long Walk releases in theatres on Friday (September 12).