Marisa Miller is in great shape, so it's only natural that the Victoria's Secret/Sports Illustrated swimsuit beauty would grace the cover of the new Shape magazine -- for the eighth time -- on newsstands January 24.

Marisa gets candid in the new issue, talking about everything from her wild side and favorite exercise regimens to how people used to make fun of her in high school.

"They called me 'bubble butt' -- but I'm over it!" Marisa tells the fitness magazine, explaining that she and a friend in high school "refused to do squats at volleyball practice because we didn't want [our butts] to get any bigger."

These days, Marisa says she works hard to tone her tush: "Muscle starts to disappear as you age, I've discovered. I love my butt and want to make sure it stays where it is. I was just talking to that same friend and we were laughing because now all we want to do is lots of squats to keep our rear ends curvy and feeling strong."

Marisa also straps on the boxing gloves and steps in the ring three or four times a week to help keep in shape. "I've tried Pilates and yoga, but they're a little too meditative for me," she explains. "I go to a down-and-dirty boxing gym. I don't want to worry about how I look or whether I'm wearing the perfect outfit. For me, it's about focusing for an hour and a half on my workout."

That workout includes jumping rope for 15-20 minutes, three-minute rounds hitting the heavy bag or her trainer's mitts with one-minute breaks, and five sets of 30-40 squats.

As for that wild side, Marisa reveals that she hops on her motorcycle in Santa Cruz, CA.

"Being outside in nature is so freeing for me," she says. "And whenever I really focus on something -- whether it's surfing, biking, or cooking - that's how I de-stress. But I also love the challenge. Riding my motorcycle builds my self-esteem and confidence."

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