When Britney Spears performed at the House of Blues in San Diego last night, she showed off her buff bod. Just how did Spears get her figure back? According to Us Weekly, it wasn’t those fat dissolving injections she’s rumored to have gotten. No, Britney got toned the old fashioned way: at the gym.

Spears’s current trainer is Manny Bujold of the Malibu Gym. He’s been getting the popstar in shape with kickboxing, treadmill and resistance-band sweat sessions four days a week. Says Bujold to Us, “It’s no-nonsense when she’s working. She comes ready to push herself…[She] busts her ass.�

Britney’s hard work has definitely paid off. In Touch Weekly reports that just last week she fit into a size 0 dress at a Los Angeles clothing boutique called Sweetpeas & Snapshots. Suzi Finer, the store’s owner, said, “The last person who fit into that dress was a 9-year-old child. No one could fit into it…[Britney] did not have one ounce of fat on her back.�