When Josh Hutcherson was cast as the kindhearted Peeta Mellark in The Hunger Games (in theaters March 23), there was a caveat: he had to totally alter his appearance.

"I dyed my hair blonde," the brunette 19-year-old said during a press junket for the film in Beverly Hills March 4. "I had to put on a lot of weight, so I was in the process of eating chicken, eggs and protein and all that fun stuff."

PHOTOS: What to expect in The Hunger Games movie

Hutcherson also exercised with "epic trainer" Logan Hood. "He was this ex-Navy Seal guy who just kicks ass."

Hood, who also worked with Liam Hemsworth, 22, had Hutcherson "flipping tires the parking lot and slamming baseball bats against body bags -- crazy things! It was so unconventional, and you're working muscles you didn't even know you had. You're like, 'How am I possibly this sore?'"

Hutcherson added: "I felt like with Logan, I was sore for four days afterwards, and we worked out five days a week, so I was in a constant state of soreness!"

VIDEO: Watch Katniss meet Cinna for the first time in The Hunger Games

Hemsworth vouched for his costar, saying: "I worked out with him for an hour and literally I would have to lay down for 20 minutes because I couldn't drive away. It would be dangerous to drive away straight afterwards! I was going to pass out."

For much more on the movie, including 125 gorgeous photos and exclusive interviews, pick up Us Weekly's Hunger Games special -- available on newsstands now. Order it today!

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