Miles Teller is no stranger to "going method" for his roles: He trained and dieted for eight months to film Bleed For This, last year's boxing biopic, and like his character in the Oscar-winning drama Whiplash (2014), he practised playing the drums till his fingers bled.
The actor had to muster a whole new level of dedication to play a firefighter in Only The Brave, the true story of the men who faced one of the deadliest wildfires in recent American history.
Speaking to The Straits Times and other press in Los Angeles recently, Teller, 30, admits he "underestimated the physical aspects" of the role, which sees him portray real-life wildland firefighter Brendan McDonough.
"I knew it was going to be tough, but I wasn't well-versed about hotshot training before I showed up," the actor says.
"Hotshots" are skilled teams of firefighters that criss-cross the United States battling out-of-control wildfires.
The film, which opens in Singapore today, tells the heartbreaking story of the Granite Mountain Hotshots, who found themselves facing a particularly devastating blaze in Arizona in 2013.
But we put ourselves in a situation where there was no comfort – and there were no laggards, there was no entitlement. Everybody had a lot of respect for the story and so was willing to give 150 per cent.
JOSH BROLIN, on filming Only The Brave
Director Joseph Kosinski (Tron: Legacy, 2010) sent 20 of his actors for a short but intense version of the punishing training regimen wildland firefighters undergo.
"It's a specialised form of firefighting," the film-maker explains.
"Unlike structural firefighters, they do not use water - they dig lines, cut trees and use fire against fire to try and corral and control wildfires."
These men are often battling flames in 38-plus deg C weather, carrying 20kg packs on their backs and wielding heavy tools such as chainsaws, he adds.
So "they're extremely physically fit, as these actors found out when we put them through hotshot camp to get them in shape".
Teller and co-stars such as Josh Brolin and Taylor Kitsch (True Detective, 2015), who play members of the Granite Mountain team, had to get in shape in the scorching summer heat of New Mexico, where the movie was filmed.
They found themselves frequently out of breath and not just from the exertion, Teller recalls.
"We were hiking and we shot in Santa Fe, which I also didn't know is the highest-altitude capital in the country - it's like 2,200m above sea level and we were shooting in some locations that were 3,000m above.
"Josh was giving everyone chlorophyll to help their blood oxygenate better."
The whole experience was "a kick in the butt", says the star, who is engaged to model Keleigh Sperry, 25. "And as far as a cast rehearsal goes, I don't think anything brings you closer together than collective suffering."
Brolin, 49, says what the cast went through pales in comparison with the real thing, but none of the actors shirked or complained because they knew it gave them valuable insights into their characters.
"We want you to think we went through hell in order to become a hotshot - the truth of the matter is, you'll never be a hotshot," says the No Country For Old Men (2007) star.
"But we put ourselves in a situation where there was no comfort - and there were no laggards, there was no entitlement. Everybody had a lot of respect for the story so was willing to give 150 per cent."
Telling a true story also made it more meaningful for everyone involved - especially with real-life firefighters such as McDonough advising them on set.
"As an actor, you want to be involved in the story when you choose a movie that resonates, and it becomes very personal," says Brolin, who is married to model Katherine Boyd, 30, and has two adult children from a previous marriage.
"So it was very emotional for everybody, and after (making) 50something movies, this is the most communal experience that I've had."
Jeff Bridges - who plays the city official in charge of the firefighters - says the cast and crew "really wanted to do justice to the tale we're telling".
The result might just inspire ordinary folks to acts of courage, too, says the 67-year-old Oscar winner (Crazy Heart, 2009), who is married to actress Susan Geston, 63, and has three adult daughters.
"Bravery is such an interesting thing - is it a reflexive thing or does it take practice to engage in and to be at peace in uncomfortable situations?
"That's something that all of us can look at in our own lives. We live in a world now that to me feels very volatile and what is our response to that? This can inspire you to take action and engage."
•Only The Brave opens in Singapore today.