"A lot of weightlifting, a lot of protein shakes," Stone confessed of how she bulked up. "I never did it before and I loved it."
"For the first three weeks, you hate your life, and I know a lot of people hate exercising. I did. And then after three weeks when you're, 'I can lift this? I can do this?' It just becomes addictive," she explained. "It's just really incredible to feel strong. It feels so good."
Battle of the Sexes depicts the epic 1973 match between King and then 55-year-old Bobby Riggs, who is played by Steve Carell. And while the actor went through a physical transformation of his own, it's his cosmetic changes people can't get over.
"I read a review that talked about how bad my wig was, and it wasn't a wig," he admitted. "It was my hair."