LOS ANGELES (AP) — Jason Clarke was already an avid outdoorsman when he signed on to play the lead role in "Everest." He'd visited most of the national parks in North America and trekked through Chile and Argentina. He knew his way around an ice-ax and crampons. He even backpacked to Everest base camp — a staggering 17,600 feet above sea level — a few years back just for fun.
But just like his less-outdoorsy colleagues, Clarke had to physically prepare for the challenges of working at extreme elevation to make the epic drama.
"I loved it," he beamed. "I loved every single second of it."
Clarke leads the ensemble cast of "Everest," opening Friday, which tells the story of the doomed 1996 expedition that claimed the lives of eight climbers — the deadliest day on the mountain at the time. To scale the planet's highest peak on screen, the actors — Clarke, Josh Brolin, Jake Gyllenhaal, John Hawkes and Michael Kelly — had to train like real mountaineers.
Director Balthasar Kormakur insisted on authenticity, so he brought his cast and crew to Nepal, where they filmed at an altitude of 16,000 feet. (The highest ski resorts in the U.S. top out around 13,000 feet. Most are less than 10,000 feet tall.)
High altitude has an undeniable effect on human function. With less available oxygen, the mind slows and the body weakens. Even expert climbers can get altitude sickness, characterized by headache, nausea, dizziness and exhaustion.
Where climbers experience gradual elevation gain during their ascent that helps them acclimatize to the thinner air, the "Everest" cast and crew were flown in. Advance preparation was essential, and still sometimes insufficient.
"We were dropped off in helicopters at the end because it was too hard to walk up there and then shoot a scene," Kormakur said. "At that point, I just saw the crew start falling apart. People got sick. We had to evacuate them."
Other snowy sequences were filmed in the Italian alps at around 12,000 feet — still high enough to cause the aches and foggy thought associated with being at high altitude.
To work up there, the actors had to become hikers months before production began — which suited Clarke and Brolin just fine.
Brolin was already a rock climber, and he used the film as an excuse to up his outdoor game. He spent seven months training, climbing on Switzerland's famous Eiger and summiting California's Mts. Shasta and Whitney.
"This is selfish to me," he said. "I got to do all the things I love to do and I got to do it in an extreme fashion that I probably wouldn't have if I didn't have the excuse of doing a movie."
Brolin plays Beck Weathers, who miraculously survived the fated 1996 Everest expedition, despite spending 18 hours stranded on the mountain, weathering its extreme conditions. He lost his hands and nose to frostbite. His book, "Left for Dead: My Journey Home From Everest," served as an inspiration for the film.
Actors Hawkes and Kelly, who wouldn't consider themselves mountaineers, each hiked to ready for their roles. Still, they felt the wearying effects of working at high elevation.
"There was a part of you going, 'I'm light-headed, I'm not thinking clearly,'" Hawkes said, "but it also affords you a chance to really not act and just be in the moment, which is a great gift for actors."
Ironically, the cast said the most physically challenging aspect of making "Everest" happened on a London soundstage. That's where Kormakur captured his close-ups: a turbine engine pelting the actors with bits of plastic, paper and salt to mimic a snowstorm. Brolin joked that the resulting exfoliation was great for his complexion.
Despite the forced skin treatment and struggles with elevation, the awesomeness of seeing Everest is something the cast won't soon forget.
"It just made me feel like I wanted to get rid of everything," Hawkes said. "It takes so little to live and to be happy."
Kelly found hiking there "incredibly grounding."
"I'll walk this trail and someone's going to walk this trail 100 years from now. And then 200 years from now," he said. "And people walked it hundreds of years before me. That's pretty cool."
For Clarke, already intimate with nature's majesty, being on THE mountain was deeply moving. He talked its top helicopter pilot into flying him up as high as they could go (around 23,000 feet).
"I said, 'I'm No. 1 on the call sheet. Take me up to Everest!" Clarke said. "It was just insane. You come around up the valley, across the ice fall — you can see the ice fall — and we're hovering and you can feel the air... Holy hell, there it is in all its glory. That's Everest. The highest peak. It was everything."
Follow AP Entertainment Writer Sandy Cohen at www.twitter.com/APSandy .