It is the first time she has ever played a real life person and Emma Stone has certainly thrown herself into it with 'Battle of the Sexes'. In fact, she trained so hard to portray tennis hero Billie Jean King that she ended up gaining 15 pounds of muscle.

Emma Stone at 'Battle of the Sexes' screeningEmma Stone at 'Battle of the Sexes' screening

The 28-year-old had to learn how to play tennis for real for the new movie, which depicts the iconic mixed-sex match between Billie Jean and Bobby Riggs in 1973 which ended with the former beating the latter in a sweeping victory. But Emma's preparation showed mind-blowing dedication; and she didn't even mind the weight gain.

'She took it seriously', her trainer Jason Walsh told USA Today. 'She wanted to do the story justice.' 

Thus, Emma's petite frame was transformed with a series of dumbbell exercises, 300-pound hip thrusts, weighted push ups and 185 pound deadlifts. She avoided cardio altogether while she was bulking up, though that wouldn't necessarily be recommended for a woman's general health.

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'We wanted to give Emma the psychological backing', he continued. 'She needed to be resilient and to have the psyche of being really strong.'

'I was pretty proud', he adds.

As for her diet plan, she was taking in hundreds of calories a day with high-protein shakes featuring ingredients like spinach and ashwagandha. It might not sound particularly appetising, but after all that working out she was eating anything that would keep her strength up.

'It wasn't like we were taking someone off the Taco Bell diet, but we added shakes into her diet', he revealed.

The upcoming movie is being directed by Jonathan Dayton and Valerie Faris ('Ruby Sparks', 'Little Miss Sunshine'), with a screenplay written by the Academy Award nominated Simon Beaufoy ('Slumdog Millionaire', '127 Hours'). 

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'Battle of the Sexes' is due for release in the UK on November 24th 2017.