The intense workout that got Emma Stone ready for “Battle of the Sexes”

Emma Stone trained with a tennis coach to practice her strokes and get super-agile on the court for her role in the new movie Battle of the Sexes. But the workouts that transformed the actress’ body to resemble tennis great Billie Jean King had nothing to do with volleys, serves, and backhands.

Stone did tons of heavy lifting with Jason Walsh, a celebrity trainer and founder of Rise Nation in Los Angeles, for about three months before filming the movie, which tells the story of King’s historic 1973 match against male tennis champ Bobby Riggs.

So much, in fact, that the svelte actress packed 15 pounds of lean muscle onto her frame.

She was fresh off filming La La Land (Walsh whipped her into shape for that role too), so Stone was still rocking the sleek physique of a dancer. “Obviously that’s going to be a major change, going from dancer to one of the greatest tennis players of all time,” says Walsh. “I had to get her to look and feel the part.”

“My focus was to give Emma that athletic prowess and resiliency.”

To create the training plan, Walsh considered the mindset Stone would need to play King. “My focus was to give her that athletic prowess and resiliency and get her feeling comfortable in her own skin on the court. There’s nothing I like more than empowering women so they feel powerful and confident onscreen.”

The trainer had already established a foundation of movement with Stone while training for her Oscar-winning La La Land performance, so he didn’t have to work on the basics with her. They jumped right in and increased the volume and stress they were placing on her muscles. Five days a week, Stone worked with Walsh, sometimes knocking out two sessions daily leading up to filming. (Once the filming was under way, the pair tapered off to three weekly workouts for maintenance.) They’d focus on strength in the morning workouts—doing moves like pulling and pushing a heavy sled (they ramped up to 200 pounds!), lower-body exercises like squats and lunges, and weighted carries.

Walsh also added stability-challenging moves, like single-leg squats, because they pack lots of strengthening power. “It’s a common misconception that balance and stability are the same thing,” he says. Stability, which you need during single-leg moves, requires major strength in your core and in and around joints like your knees.

“Emma is a tiny woman,” Walsh says, “but she is strong as hell.”

For those two-a-days, Walsh took Stone through afternoon workouts targeting secondary, smaller muscles (to fine-tune her physique), and they’d have conditioning sessions using the VersaClimber (the intense vertical-climbing machine) at Rise Nation once or twice weekly. Stone also started eating more calories to help her body adapt to the rigorous training.

“In the beginning, with the increased volume, it was stressful and tough—most of the exercises were daunting,” says Walsh. But Stone adapted and pretty soon, it got more fun—and she got way strong: She worked up to deadlifting 185 pounds (which Walsh calls “insane”), hip thrusting 300 pounds, and doing single-leg squats with 80 to 90 pounds—further proof that lifting heavy doesn’t bulk you up.

“Emma is a tiny woman,” Walsh says, “but she is strong as hell.” Too late to add a fitspo category to this year’s Oscars?  

Emma fans, these are for you: A guide to her La La Land sweat sessions, plus her advice on living with anxiety.