In the fact-based film, Bleed For This, cocky Rhode Island boxer Vinny Pazienza (Miles Teller) takes a brutal beating from Junior Welterweight Champion Roger Mayweather in 1988. After his humiliating loss, fight promoter Lou Duva (Ted Levine) urges him to retire. Instead, Pazienza moves up two weight classes under the guidance of his new trainer Kevin Rooney (Aaron Eckhart). Rooney’s radical strategy pays off when Pazienza, 14 pounds heavier, takes down French boxer Gilbert Delé in front of a hometown crowd to become Super Middleweight champion of the world.

Pazienza doesn’t have much time to relish the victory, however. Shortly after the bout, a head-on car crash leaves him with a broken neck. Initially told he may never walk again, doctors recommend spinal fusion surgery that would guarantee mobility but effectively end his boxing career. Pazienza chooses the far riskier “halo” spine-stabilization treatment, requiring him to wear a circular metal brace screwed directly into his skull for six months.

Recovering in the modest home he shares with his fiercely devoted father Angelo (Ciarán Hinds) and anxious mother Louise (Katey Sagal), Pazienza secretly starts weight training in the basement with the help of a reluctant Rooney and begins to recover both emotionally and physically. 13 months after the accident, the man fondly known as “The Pazmanian Devil” returns to the ring to do battle with Super Middleweight Champion Roberto Duran (Edwin Rodriguez) in the biggest fight of his life.

For their roles, Teller had to bulk up while Eckhart had to flab up. While some attractive actors are leery about gaining weight for a role, Eckhart dived right in to the deep end of the deep dish.

“We’re playing real people and that’s what he looked like. He was a fighter at one time. He trained with Cus D’Amato who was the greatest trainer and a boxer himself. [D’Amato] gave up his career to train [Mike] Tyson. When he was fired from Tyson’s camp, it was sort of the beginning of the end for Kevin. He took a psychological hit and gained weight. He started gambling and drinking. He was really at the bottom when he met Vinny. I gained 40 pounds to get into that head space. I’m a pretty active person so I just circled a date on the calendar and said, ‘after that date, there’s no more jumping rope. There’s no more riding my bike or going to the gym.’ I went from arugula to pepperoni pizzas everyday. I saw a nutritionist in the beginning and she put me on fava beans or whatever. I said that wasn’t going to work so I went back to the pizzas.”

It can be a shock to the system when someone must gain or lose a lot of weight in a short period of time. Eckhart, however, had been through the process before, so he knew what to expect.

“I’ve [gained weight] two times before. I did it for Your Friends and Neighbors. I gained 45 or 50 for that. When you get older, it gets harder because it’s harder to lose and it has effects on your skin in terms of stretching your body out. I’m glad I did it. It really put me in the place I needed to be. It lets the audience believe in the character and forget about me. That’s the comment I get most from people is that they either don’t recognize that it’s me in the movie or they let the character take over. Going from one physicality to the next – either gaining or losing weight – it has an effect on how you see yourself and how you think others perceive you.

I probably felt like Kevin felt in a lot of ways. For months, I didn’t button the top button on my jeans. I went for a walk with my then-girlfriend on a beautiful autumnal day and I said, ‘babe, I’ve to stop and buy some baby powder to put between my legs’ because I was chafing. It wasn’t that romantic. The other thing is that I went on another walk with her and I got poison oak all over my backside. I did this entire movie with poison oak all over my backside. It probably added to the angst of my character.”

I mentioned that it was probably good then that he didn’t have a nude scene in the movie.

“That’s right [laughing]. I did, but it was cut out. I did take off my shirt at one point in this movie in a strip club, but it was cut out. But I did go all the way.”

Bleed For This is Eckhart’s third film of 2016 and his second in which he portrays a real life person after Sully. That’s always a challenge for any actor, but it’s a challenge Eckhart relishes.

“There’s pressure but I like it. Kevin is still alive though he’s in the hospital with dementia. Jeff Skiles [his Sully counterpart] is alive. It’s great because they’re there for you. Yes, you have to get their mannerisms and behavior, but you have all the information you need. You don’t have to create that. You have to stick to the information you’re given. It’s a different challenge. Unfortunately, Kevin is in the hospital but I worked with his son. I went through training camp with Manny Pacquiao and [Timothy] Bradley at their first fight. [Trainer and Pacquiao coach] Freddie Roach let me be a fly on the wall. I went to their training camp. I was in the training room before and after the fight. I was ringside with [boxing commentator] Larry Merchant. Everything that I do with Vinny, Freddie Roach taught me because Kevin couldn’t. I got a very good education.”

If you’re going to spend months working on a movie about boxing, it helps the process if you’re a boxing fan. Not only is Eckhart a fan, he’s a boxer himself and understands the nuances that it takes to be a successful boxer.

“It’s about technique. It’s about using your entire body to throw a punch from the ground up. To be able to do that with an opponent, it takes years. I’ve been boxing for 20 years. When I did Erin Brockovich, I had to get in shape for that. I said to myself, ‘hey, I have to get in shape for this Hollywood career. I’m going to learn a skill.’ I chose boxing. I do it every single day. It really helped me out in this movie. I always tell young actors that you have to know how to do three things. You have to know how to ride a horse, shoot a gun and throw a punch. If you learn those things early, you’re going to do that in your career. It’s better to have the technique down so that you can forget about it. I watch people hold guns all the time and it just doesn’t look true. Your entire credibility as a character – all the work you’ve done emotionally – goes out the window.”

In the film, family is a big part of Vinny’s life – and success. Eckhart echoes the sentiment that family bond in strong in the boxing community.

“If you go to Freddie’s gym or Kevin’s gym, you always see a brother or a best friend. I can’t tell you how many people Manny had around him. They give you confidence but you also need that buffer. I watched plenty of video of Kevin with Tyson. They were just inseparable and they talked about everything. You need that support. You need that person that you can look at and say, ‘we’re in this together.’ There’s also a bond between fighters. In any high level sport, you’re basically trying to talk yourself out of it.

As an actor, I’m always trying to talk myself out of doing a job because it’s so scary. You’re so vulnerable. You can get physically knocked out or figuratively knocked out. You need people around you to help you combat your fears – your fear of failure; your fear of not being good enough. This character was probably the hardest one I’ve ever done in my life. I’m not an accent guy. I don’t want to fail. I don’t want to look stupid. I don’t want to be embarrassed. I don’t want my director to say, ‘you didn’t do it. You couldn’t go there.’ Everyone was just so committed to this movie. You could not look around anywhere on this set and say that nobody was not there. Everybody was challenging each other. Everybody was such a good actor and you don’t want to be the worst. Fear is a great motivating factor.”

Bleed For This is now playing in theaters.