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At 22, there's a lot to love about rising star Shailene Woodley: She's passionate about the environment, wears used clothes, and prefers bare feet to Louboutins. To add to that list: Woodley did her own stunts for her highly anticipated new film Divergent. "If you don't get a few bumps and bruises when signing on to an action movie, you're not doing something right," she says.

In order to become Tinseltown's newest action heroine, she turned to legendary stunt master Garret Warren, who has taught martial arts and fight choreography to A-list celebs like Jada Pinkett Smith, Jessica Alba, and The Rock. We went one-on-one with Warren for the inside scoop on how he transformed Woodley into fierce, fighting shape for her gun-toting, knife-throwing, butt-kicking role.

Shape: Why was it so important for Shailene to train specifically for this role?

Garrett Warren [GW]: Shailene's character comes in and she's not supposed to know how to fight-so that worked for us, because that's who she is as a character. The sequences turned out to be interesting fights rather than blockbuster action. By the end of the movie, Shailene's character is a well-oiled machine. She isn't a superhero. She's a real person who works hard yet has her weaknesses like anyone else.

Shape: We heard she did many of her own stunts. How dangerous were they?

GW: One of the hardest stunts was standing 35 feet in the air on the edge of a building with only a safety cable. One night in Chicago, she also climbed up the side of a Ferris wheel with 75-foot ladders. That's why we did supersets, lots of reps, and few breaks. She needed endurance the entire day, every day.

Shape: Tell us more about the training.

GW: We'd do body movements like pushups, chin-ups, dips, squats, lunges, and plyometrics for 30 minutes, then we'd move into fight choreography for 30 minutes: jiu-jitsu, judo, close-quarter combat situations, krav maga, boxing, and muay Thai. After that we'd learn how to throw knives into targets. It was an intense bootcamp that involved shooting firearms and hand-to-hand fighting too. We started again five weeks before the movie started with the same routine, but we added weight work and functional training. We always did her whole body but different exercises each day.

Shape: What were some of your specific goals?

GW: We had to worry about not working out too heavily. The workouts weren't for building muscle but rather for building the endurance for the dozens of takes of jumping off trains, climbing up ladders, and shooting guns.

Shape: What was the biggest change you saw in Shailene post-training?

GW: Her posture and confidence were amazing. She held herself really well when she first came in, but by the end she had such a strong posture.

Shape: Did you do anything special with her diet for the role?

GW: She was already eating healthy. She didn't really eat candy or fried foods, or drink alcohol. I just encouraged her to eat smaller meals more frequently. We also tried to cut out salty foods so she wasn't bloated on set.

For more info on Garrett Warren, follow him on Twitter @GWarren333.