The two stars, who portray Roberto Duran and Sugar Ray Leonard in the film, had to adopt drastic fitness methods to look like toned welterweight fighters, and Venezuelan Ramirez admits he and the singer-turned-actor were literally starving for much of the movie.

"It was horrible," he tells WENN. "Diet was a very big part of the process. Each of us had to lose maybe 25 to 30 pounds."

And shooting the movie in Duran's native Panama didn't help, as Edgar's co-star Ana de Armas explains: "We have beer and rice and beans and chicken and plantains and all this yummy food you want to eat. That was not possible for Edgar!"

"We would get together with some other members of the cast and the crew for gatherings and they would want me to come by," he recalls with a grimace. "I would say, 'I can't because you're going to be drinking beer and having amazing food. It's gonna be torture for me'."

But the strict diets helped Usher and Edgar get into the mind of a boxer: "By the time we were filming the fight scenes, we understood the mentality of a boxer. You have to sleep like a boxer, you have to eat like a boxer, and train like a boxer. But losing that weight really messes with your head. It gave me a neurosis that was really interesting to explore."

The film, also featuring Robert De Niro, Ellen Barkin, and John Turturro, punched its way into cinemas at the end of last month (Aug16).