Britney Spears is looking better than ever, as she embarks on her two-year residence at the Las Vegas Planet Hollywood beginning later this year.

With the help of her personal trainer Tony Martinez, the Ooh La La singer is hitting the gym at least three days a week.

"She is focusing on high-intensity intervals, along with cardio at least three times a week that includes sprints, jumping rope, basketball drills and boxing," Martinez told EnStars. "Changing her workouts each time is the key to her success."

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The pop star -- and mom of two -- has a packed schedule full of meetings and rehearsals, so the workout is focused to fit her busy lifestyle.

"My workout motto is work out smarter, not longer," the celebrity trainer said. "When we first met, she wanted to run on the treadmill for two hours. But I've shown her ways to sculpt her body that take less than 20 minutes. Now she's loving these quick workouts."

The celebrity trainer revealed Spears is always on time for the gym and "ready to work" when she gets there.

"She is sassy and very competitive. She'll be like, 'Is this all you got?'" he recalled. "She is a great athlete and makes working out look easy. She wants to be in the best shape possible, and she is very happy with her body right now."

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In addition to working out, Spears also following a healthy diet. In an interview with Shape Magazine, Spears admitted she's eating low-calorie meals on the Nutrisystem diet.

"Smart nutrition is half the battle. I try to help her understand portion size and help her choose healthy options," Martinez added.

Britney, Piece of Me, will be an action-packed performance hybrid of her old and new hits where club meets theater, Spears revealed about her Las Vegas show on Tuesday morning during Good Morning America. The show will debut Dec. 27.

"We wanted the environment to be that way so people could come and have a good time and stand up and feel like they're in the show with me," Spears told "GMA." "I love Vegas. The energy here is really, really good."

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To find out more about celebrity trainer Tony Martinez, check out his website: www.trainertonymartinez.com.