Sydney Sweeney is opening up about her dramatic transformation to portray legendary boxer Christy Martin in an upcoming biopic. In a new interview with W Magazine published Monday, the actress revealed she spent months training for the role, gaining 30 pounds and going up four pant sizes in the process.

For context, Sydney is starring as Christy Martin — the American fighter known for putting women’s boxing on the map in the mid ‘90s — in a biopic due to release later this year. Speaking to W Magazine for a brand new cover, it was revealed that Sydney gained over 30 pounds to play the part.