In "Bleed for This," Miles Teller had to be a real knockout — but not the kind you might expect.
As it turned out, the "Divergent" and "Whiplash" star recently got into serious shape to star in the true story of world champion boxer Vinny Paz, who made a comeback after breaking his neck in a car accident.
And for Teller to get in shape, he'd have to hit the gym hard. "We filmed this two years ago, but I lost 20 pounds and got down to 6 percent body fat and then I had to gain 15 pounds back when we were filming," he recalled on TODAY Wednesday.
RELATED: Miles Teller shares the adorable nickname his mother gave him
It couldn't have been easy: In real life, Paz had to wear a neck and head brace called a halo for months, during which he still continued to work out. To learn how, Teller says he went to the now 53-year-old source.
"Vinny is the only person who can tell you how to bench press with a halo on," he recalled. "There's no other person in the world who can speak with any authority on that.... It was really special."

Still, when he got the call to play the role, Teller admits he wasn't sure why his name even came up. "I certainly don't think I was the guy studios were calling to be a five-time world champion Italian-American boxer," he chuckled.
RELATED: Truly ‘Awkward’: Zac Efron, Miles Teller talk ATV rides, lobster socks
Now that the film's out, while Teller still looks pretty fit to us, he says his shape is more back to an average human being's. "I wish I still looked like that," he said. "That was a fleeting moment in my life."

"Bleed for This" opens in theaters on Nov. 18.
Follow Randee Dawn on Twitter.