Unsurprisingly, it took a lot of hard work in the gym for her to prep for this role.

“She knew she’d be playing one of the greatest athletes ever.

She took it really seriously,” Walsh adds.

Emma Stone Battle of the Sexes premiere

Michael Tran / Getty Images

Still, Stone is just as goofy in the gym as you’d imagine.

“Shes really really good at breaking me with laughter,” Walsh says.

Here’s what Stone did to physically prepare for her epic role.

Emma Stone and Steve Carrell

Emma Stone stars with Steve Carrell in the upcoming “Battle of the Sexes,” where Stone plays tennis legend Billie Jean King.

“We had three months to get her to look and feel like an athlete,” Walsh says.

As she progressed, she loved noticing that she was stronger.

“She smiled ear to ear,” when she reached her goal, he says.

Emma Stone in Battle of the Sexes

Actress Emma Stone spent three months in the gym to build the muscle and fitness she would need to play tennis star Billie Jean King in “Battle of the Sexes."

“The science of training today is meant to keep athletes healthy, keep them on the field.”

“Thats a lot of pressure on a trainers shoulders,” Walsh says.

An important factor here is that Stone started training a few months out.

“Im not going to take on that responsibility if we dont have time to do it.”

Yes, some days that meant two workouts per dayan a.m. session and a p.m. session.

“We increased [Stone’s] caloric intake to approximately 2,500 to 3,000 calories a day.”

She also relied on high-calorie shakes right after each workout to supplement her caloric intake.

“Its a huge psychological advantage to feel really comfortable in your own skin.

I think it helps even with the character,” he says.

Sounds like Stone’s got that whole foundation thing handled.

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