Ashley Olsen does pilates almost daily in order to stay in shape.
The 31-year-old fashion designer employs trainer Jessica Schatz in Los Angeles, and she's revealed the secret to her slim figure.
Jessica explained: "She is extremely strong and works incredibly hard."
Jessica focuses her fitness programme on core work, and has revealed that Ashley's workouts are a mix of Pilates and yoga.
Jessica told PEOPLE: "While the work is rooted in Pilates, I combine all of my expertise to offer her an incredibly strong workout based on core strength, core stability, and core control.
"I also combine my expertise in yoga and biomechanics to keep things tailored to her specific body."
Jessica also revealed the specific exercises she runs through with her celebrity client.
She shared: "We do a lot of planks and variations of planks, like reverse planks, and side body core and leg work."
What's more, Jessica paid tribute to Ashley's self-discipline, which helps her to stay in good shape.
The trainer explained: "Ashley is extremely disciplined, hard working and open to trying anything new."
Meanwhile, Hollywood actress Elizabeth Olsen previously hailed her sisters Ashley and Mary-Kate as "brilliant women" who have achieved everything they dreamt of and more.
The 'Avengers: Age of Ultron' star said: "I just think they're brilliant women. [On their shops they're like,] 'I like this. I like this world. I like art, I like architecture, I like photography, I like fashion,' and they've made it into a company."
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