Britney's Trainer:

The key to getting Britney in shape is all about having fun, says her personal trainer Tony Martinez, who helped the star get in tip-top condition for her recent Shape magazine cover. Fortunately for him, Britney isn’t obsessed about conforming to a standard, she just wants to be fit.

“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,” said Martinez. 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.”

Britney’s used to a certain workout regimen, but Tony switched it up on her.

“She was used to weights and running or cardio,” Martinez told E! News. “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.”

One drill Britney, who used to be a gymnast, is particularly fond of is the cartwheel squat, which is a cart-wheel followed by a squat. Another is the reverse basketball lunge (she was also a b-ball player in highschool!), where she dribbles a ball while performing forward lunges.

He also has her walk backwards on a treadmill to confuse the muscles.

“The hardest thing for her to do was go backwards, but she said, ‘I’m sweating more walking backwards than running and I like this.'”.

Martinez told

“I like doing stuff outside with Britney more than being in a gym. Anyone can be in a gym. I try to do more functional, athletic training. When she dances she’s doing a lot of lateral movements, so we do a lot of lateral, we do a lot of plyometrics. We try to mix it up a lot so her knee’s still good, her back, shoulders… but at the same time she’s getting strength and she looks great.”

“I push her every single time to the limit. I want to make sure that she feels every little thing possible. The thing that makes me mad is she conquers it every single time. She’s like ‘that’s all you got?’”

He added: “She’s a tremendous athlete, and she makes it easy for me.”