Sydney Sweeney gained 30 pounds to play boxer Christy Martin. She also went through about three and a half months of training, which involved weight-training in the morning for an hour, kickboxing midday for about two hours, and weight-training again at night for an hour. She said in an interview with W magazine, "My body was completely different. I didn't fit in any of my clothes. I'm usually a size 23 in jeans, and I was wearing a size 27. My b**bs got bigger. And my [bottom] got huge. It was crazy! I was like, Oh my god. But it was amazing. I was so strong, like crazy strong."
