(Photo credit: Shape magazine)

Reported by Andrea Dresdale of ABC News Radio:

Britney Spears graces the cover of the June issue of Shape magazine, rocking a white bikini and a pierced navel. Inside, she reveals her fitness secrets, and also confirms that she's definitely doing that long-rumored Las Vegas residency, starting this fall.

Explaining how she keeps her 31-year-old body in shape, this mother of two tells Shape that she does 90 minutes of yoga twice a week, as well as hour-long cardio sessions three times a week with her trainer.

"The [Vegas] performances won't be simple … a massive party from start to finish," she tells the magazine, on newsstands May 20. "And to pull this off, I have to be in top condition and running at full speed."

And what about the music this pop star sensation enjoys listening to when she works out? She says Bruno Mars' "Locked Out of Heaven" and Whitney Houston's "I Wanna Dance With Somebody" are two of her current favorites.

Spears also reveals that she does Nutrisystem - a shake for breakfast and lunch, plus protein and vegetables for dinner, so she can avoid eating the snacks, such as chocolate chip cookies, her two sons enjoy.

"I try not to make those too often, or I'll eat the whole bowl of dough," she tells Shape.