While working hard to get her life back on track, Spears decided she wants her before-a-baby body back, too. Life & Style reports Spears puts in several hours a day at the gym and loves every minute of it.

"She's hell-bent on getting a rocking midsection again," Britney's personal trainer, Marc Corliss, told the magazine. "She's been training hard for the past four weeks, doing about 500 or so abdominal exercises ever day. And she's seeing a major difference already."

It seems like the workouts also function as a mood-booster for the singer, who told Life & Style, "I'm always happy when I'm done."

Brit's father even gets in on the fitness act, said an onlooker who spied Jamie working out alongside his daughter at Studio City's Bally Total Fitness. "It's really cute; he'll spot her on some of the machines. She seems like a kid around him."

Already 15 pounds lighter for her efforts, Britney's only weakness now comes after the exercises.

"She comes home from the gym and wants to splurge on cookies and ice cream and junk," said a friend. "It's always a fight for her to resist all that."