Britney Spears has been getting into fighting form for her latest stint in Las Vegas, and for good reason. The 31-year-old is set to make $15 million a year while performing at Planet Hollywood. The singer will perform 48 shows each year for two years.

Spears has been showing off a slim and trim bikini body ahead of her shows, and her trainer, Tony Martinez, revealed how she lost the weight back in July. The 31-year-old mother of two boys first showed off her new figure on May’s cover of Shape magazine and flaunted flat, toned abs.

Martinez, who has also trained celebrities such as Pink and Janet Jackson, told E! at the time, “She is a tremendous athlete. She likes to be very strong and aggressive in her workouts. I kept telling her to stop making it look too easy. It was like a competition with us! He has instructed her to eat small meals five times a day, with her favorite meal being chicken salad with balsamic dressing.”

The “Work B-tch” singer follows the Nutrisystem weight loss program, where meals consist of a shake for breakfast and lunch, plus a dinner of protein and vegetables in order to stay healthy. She also does yoga and cardio to stay fit.

“I’m doing 90 minutes of yoga twice a week in addition to a lot of cardio -- hourlong sessions three times a week with my trainer,” Spears said. “The [Vegas] performances won’t be simple -- they’ll be a massive party from start to finish, and, to pull this off, I have to be in top condition and running at full speed." TMZ reports that Spears will earn $310,000 per show and the producers are aiming for a “cool, hip, club-like show,” which should not be a stretch for the pop star. The shows begin in December.