Sydney Sweeney gained 14 kg for her role as a boxer. How did she train?

How long did it take the Hollywood star to gain that much weight? And what did she reveal about her new film?

The actress decided to go all-in — this time for the role of Christy Martin, one of the first stars of women's boxing in the US and the first female boxer inducted into the Nevada Boxing Hall of Fame. For this biographical drama hitting theaters later this year, the actress transformed herself beyond recognition.

Director David Michôd told W Magazine that Sydney gained more than 30 pounds (about 14 kg) to play the athlete who stepped into the ring on Mike Tyson's undercard in the '90s, landed on the cover of Sports Illustrated, and basically put women's boxing on the map.

Actress Sydney Sweeney in a red tank top showing off her bicep — Sydney Sweeney as female boxer Christy Martin

"I was loving it," says Sydney . She had just over three months to prep. Every day meant morning strength training, then a couple hours of kickboxing, then back to the weights in the evening. The diet focused on gaining mass.

I couldn't fit into any of my clothes. I usually wear a size 23 in jeans, but I had to go up to a 27. My chest grew, my hips — like a powerlifter's. I'd look at myself and think, 'What's happening?' But at the same time — I got really strong.

Sydney Sweeney

The film's already wrapped, and Sydney first shared photos in character as Christy back in the fall. She wrote then that she had to completely immerse herself in the role, which meant not just training in the gym but actually fighting in the ring.

Actress Sydney Sweeney and boxer Christy Martin raising their fists and smiling — Sydney Sweeney and Christy Martin

The project's title hasn't been announced yet, but the story's already known: Martin's journey from ring victories to personal drama (marriage troubles).

Earlier, we at zoomboola.com reported that Sydney Sweeney might land a role in the Split Fiction video game adaptation.