Based on the clips that have been released thus far, Universal’s Atomic Blonde features a lot of ass-kicking at the hands of a Cold War spy, Lorraine, played by Charlize Theron.

Her leading role as badass spy is meant to break the stereotypes associated with female action stars, and Theron herself broke some stereotypes during production. The star set her looks aside and trained for four hours a day in preparation for filming. The Mad Max: Fury Road actress is no stranger to action, but her body took a beating in preparation for Atomic Blonde. Her training resulted in a twisted knee, bruised ribs, and multiple dental surgeries from clenching her teeth, she told Variety.

Theron admits that the training was tough, and that becoming a convincing fighter was no walk in the park. “I’m coordinated because I was a dancer, and I definitely have movement memory, but I’ve never been a fighter,” she said in the interview. “I’m also really tall and a girl. That tends to make you look like you’re Big Bird.”

And her extensive practice made perfect, because Theron looks every inch a ruthless fighter in the trailers for the film, directed by John Wick‘s David Leitch. “She’s f***king badass,” Leitch said in behind-the scenes footage of Theron’s training. Her skill level allowed them to film longer takes and more complex moves, he said.

In the film, she wasn’t afraid to break the “hot female action movie star who always manages to look flawless” stereotype and look bloodied and bruised on-screen. The focus was on authenticity, especially during and after fights.

Another standard-breaking aspect of the film is Lorraine’s love interest. Rather than fall for her colleague (played by James McAvoy), Lorraine goes for a fellow female spy (Sofia Boutella), and they “didn’t hide under the sheets,” she told Variety.

Check out Universal’s behind-the-scenes footage of Theron’s fight training below.

Atomic Blonde, starring Theron, McAvoy, and Boutella, hits theaters on July 28.