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(Yahoo!) - Whoa! Anyone else getting a flashback of old school Britney Spears?

The 31-year-old mother of two has landed the cover of Shape magazine, and in the June issue, Spears shows off her toned abs that are reminiscent of her "Baby One More Time" days in 1999.

However, 14  years later, Spears admits that maintaining her body is not as easy as it used to be...particularly when it comes to keeping her backside in shape.

"I like it, then again, I hate it," Spears says. "I’m in my 30s now, so I have to work harder to keep it 'up.'"

So what does her hard workout routine entail?

“I’m doing 90 minutes of yoga twice a week in addition to a lot of cardio — hour-long sessions three times a week with my trainer, Tony Martinez,” Spears reveals. This conditioning will get Spears in shape for her upcoming performance stint in Las Vegas. While a start date has yet to be confirmed, it is rumored Spears will perform 40 alternating weekend shows at Planet Hollywood’s PH Live.

“The [Vegas] performances won’t be simple — they’ll be a massive party from start to finish," Spears says. "And to pull this off, I have to be in top condition and running at full speed."

This also includes a more restricted diet regimen.

"Dieting is tough," the "Scream and Shout" singer admits, "because my specialties are spaghetti, brownies and chocolate chip cookies. I try not to make those too often or I’ll eat the whole bowl of dough.”