Move over Jessica Simpson -- Hilary Duff knows the real secret to shedding that baby weight!

Duff, who gave birth last March, is back in her skinny jeans and looking better than ever -- but it's no miracle, it's with the help of "piloxing" founder Viveca Jensen.

toofab's Brittany Kyles spoke to Jensen, the personal trainer who's been kicking the new mom's butt back into shape.

Piloxing is a mixture between pilates and boxing -- the cardio workout blends interval training of choreographed boxing moves with standing pilates (which can burn up to 900 calories in just one session!).

Viveca's classes target muscles that lengthen your legs, arms, triceps and back -- and to help the Disney star drop that baby weight Jensen says, "I've been kicking her ass with an ab workout and different style planks -- like from the plank position to picking up her leg from under and pulling it over her shoulder."

For new moms it's all about working your core. "You want to get you core muscles toned, it's all about correcting them again," she tells us.

One workout that Hilary loves is called "Around the World," you may have seen her tweet an image of her doing the flexible move earlier this week.

"Around the world uses a barrel -- your whole body is pushed 45 degrees while you hold one side over the barrel and up. It targets every muscle of your outer obliques," Jensen explains.

The piloxing founder and celebrity trainer has been working with Duff for over eight years -- and the blonde beauty is one of her hardest working clients.

"She's a hard working girl, and even worked really hard all through her pregnancy," Jensen says.

But getting back into shape is no easy task -- Viveca's best advice for mom's trying to drop that baby weight is to (brace yourself) ... workout everyday!

"When you're ready to come back from a pregnancy you have to kick it up to a certain level -- it's hardcore training," Viveca tells us.

For a normal person trying to stay fit, Jensen says 2 -3x per week is pretty good -- but when it comes to women with excess baby weight, it takes much more dedication because you need to strengthen those muscles again.

Hilary's problem area (like most women who've just  had a baby) is her abs -- but they're coming back!

"Abs are the weakest after a pregnancy, but piloxing really gets your abs re-connected to your back and now her [Hilary Duff] stomach is looking amazing again. We can already see contour abs coming in, it's beautiful," Viveca tells us.

The 25-year-old is not the only celebrity fan of piloxing -- Kirsten Dunst, Vanessa Hudgens, and Ashley Tisdale are also regulars of Jensen's classes.

Jensen's also personally trained  Emmy Rossum, who stars on a little show called "Shameless."

When Rossum landed the hit TV drama, the brunette actress sought Jensen's help to get her entire figure looking camera ready -- "she was coming in a lot when she started 'Shameless' and told me 'I won't have a lot of clothes on in the show, so I need to keep it tight,'" Viveca explains.

What truly makes piloxing so special (ahem, ladies), is that it targets and tones the areas of the thigh and lower back in non-stop movement, which helps shape a woman's body to look more feminine and powerful.

And on the topic of celebs, babies, and post-baby bods, Viveca says she'd love to train Kim Kardashian after she gives birth, "She would love my workouts to stay in shape and keep her feminine curves -- and I could kick her booty into tight booty shape!"

And for those of you (who like us) made a New Years resolution to lose that winter weight ... Jensen has a few words of advice, "Don't make a resolution you know you won't keep. My clients come in and say 'I want to train everyday' and I tell them if you can come in like 3x a week and stick to that, that's what I want. Don't put too high of expectations on yourself."

"Have a workout buddy and support each other, get somebody that you can check in with because sometimes it's easier to have a friend," she says.

Viveca's "Piloxing Academy" is located in Los Angeles, but she has certified trainers all over the country -- and if you're looking for a routine you can do from home, she's got her 60-Day Program (with a nutrition guide) DVD that will be available online in the next few months.

"It helps you change your lifestyle, and it's diet you can do for the rest of your life," she explains.

Make sure to visit  Piloxing.com for more information about Viveca and piloxing -- and check out more stars' post-baby bods in the gallery below!


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