And she certainly took that challenge seriously: Alicia packed on 5.5 kilograms of muscle for the role. That impressive fitness feat happened with the help of celeb trainer Magnus Lygdback (whose clients include Brittany Spears and Gal Gadot).
He worked with Alicia starting three months before the movie shoot, using the "Magnus Method"—an interval-based fitness regimen he developed. For Alicia's muscle-bulking goals, the trainer worked out with her for an hour a day, six to seven days a week, mainly focusing on heavy weight lifting and strength training exercises (think squats, pushups, chinups, medicine ball slams, etc), reports USA Today. To achieve action-hero-level agility, Lygdback also incorporated mixed martial arts (MMA) fighting into Alicia's training.
The 5’ 5” and 117-pound actress showed off some of the moves she learned from Lygdback on Entertainment Tonight, including her ability to rock pullups on the rings (while sporting a very noticeable six-pack).
As Lydback describes on his website, the method also goes beyond fitness, it's "a training philosophy that embraces the 'ethos of an athlete'—approaching life fitness with the same specific intensity and structure that an athlete would, whilst also maintaining a balanced and healthy life."
In Alicia's case, that meant getting her diet in check—and they went for the keto diet. “Since we were traveling so much over the holidays, we decided the keto diet would be best because it’s easier to control the macros that way,” he told Popsugar.
Keto is a super-strict, high-fat, very low-carb eating plan. In fact, Lydback had Alicia stick to less than 25 grams of carbs a day. (For reference a cup of blueberries contains 21 grams of carbs.) The idea is that going so low in carbs forces your body to switch to burning fat rather than carbohydrates, which is its preferred energy source. The process is called ketosis.
Alicia filled her plate with fish and seafood for protein and limited vegetables (veggies contain carbs, too). The mainstay of the program was fat in the form of MCT oil, avocado, and coconut oil, Lydback revealed. A keto diet also cuts out grains, legumes, root vegetables, most fruit, and dairy.
And yes, this is a tough one to stick with. “It’s always tricky the first couple of days, but [Alicia’s] willpower is just unbelievable and she didn’t complain, even though I could see she was struggling a little bit. She kept on bringing it every day,” Magnus said. But despite the challenge, ultimately, Alicia's hard work and dedication paid off in the muscle department.
Just check out her guns in the movie. Yeah, you know which ones we’re talking about.
This article originally appeared on Women's Health US