Britney SpearsTo look at Britney Spears, you'd say she was a total gym bunny, right?

You don't get super-hard abs for nothing, after all.

And with the amount of grinding she does on stage, she must be burning calories by the minute.

But Brit has surprised us all by confessing that she's not as fit as she used to be in her teenybopper days of old.

"I used to be a workout freak, but after I had my kids, it was a lot harder for me to get back into that routine," the starlet mum-of-two told More magazine.

"I used to love going to the gym but then as you get older and you have more responsibilities, you lose that kind of discipline.

"Even now, I have a much harder time getting mentally psyched to train, but once I'm in the gym, I start getting into it and I feel great."

Brit, who kicks off the UK leg of her Circus tour in London tonight, also revealed that she's learned how to go easy on herself.

"I'm learning to take better care of myself and not get stressed or down about things for nothing,"  the 27-year-old said.

"I'm taking my time these days and not letting myself feel any pressure other than to just feel happy about myself and to work on my music." 

Phew... just goes to show that even the most eager hip-swivelling stars need time out.