Britney Spears uses ''old-school'' routines to get fit.

The brunette beauty's fitness instructor, Tony Martinez, has revealed the star does weights and works on her cardio to get into shape, but he always makes sure she is having fun with the routines.

Tony told E! News: ''She was used to weights and running or cardio. She is old-school and would do cardio for an hour. So I said, let's do something different for twenty or thirty minutes instead. And she was huffing and puffing and she is just having fun.''

Unlike other celebrities, Britney isn't aiming for a particular size or weight, she just wants to be healthy.

Tony explained: ''One of the things about her that stands out is she doesn't have it in her head that she wants to be thin. Normally they have to be x, y, z and want to weigh 100 pounds.

''She just wants to be healthy and that is really good. She doesn't want a stick figure. She likes her athletic body. She is absolutely a role model. I think she is happy how she looks and feels good and she likes a different change of workouts for herself. She feels good about her body.''