Bjarne Jonasson / SELF 1 / 9
Bjarne Jonasson / SELF 1 / 9

For Natalie Dormer, fitness serves a dual purpose. Sure, it keeps her body looking stunning, but it also serves as an acting tool, in a way.

"When you work the unnatural hours that actors work, and when you fly as much as we do, you have to pay attention to your body—or else you're a disaster ready to happen," the "Game of Thrones" actress said.

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The 33-year-old graces of the cover of April's Self Magazine and details not only her grueling work days, but also the one fitness-related thing she takes with her everywhere.

"My yoga mat will always be in my luggage," she reveals. "Yoga is invaluable when you're on long-haul flights a lot. But I do it for my mind as much as my body. Actually, that's true of my relationship with all exercise."

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Natalie, who also stars in "Hunger Games: Mockingjay—Part 2," is a big believer in keeping up with her fitness -- for her career, if nothing else.

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"In 'Mockingjay—Part 2,' I'm basically running around in heavy armor while carrying a semiautomatic rifle," she said. "I don't know how I would have kept up with [costars] Liam Hemsworth or Sam Claflin if I hadn't been in the best cardiovascular shape of my life."

And after shooting those scenes, Natalie still did another hour of cardio. If that all sounds crazy it's because it is, even Natalie will admit that. "I actually look back on it now and think…how did I do that?'"