United Kingdom, Oct. 5 -- Sydney Sweeney spent three months training for her role in Christy.

The 28-year-old star plays female boxing trailblazer Christy Martin in the upcoming movie and overhauled both her diet and exercise regime during the time she had to prepare physically for the part.

In a Q+A at Hamptons International Film Festival, Sydney recalled: "Every morning I would weight train for an hour, then I would go and do boxing for three hours, and then another hour of weight training at night. I did that every single day for three months, with a nutritionist, so eating a bunch of food and protein shakes and supplements. I, in that span of time, gained, like, 35lbs."

Sydney explained that Christy was "very involved" during the m...