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She's got legs. She knows how to use them!

Jessica Simpson has been open about her grueling workouts, and in case you have any doubt, take a look at this girl's insanely toned legs.

The fashionista showed off her lower extremities in an Instagram photo while on vacation with a few friends at the idyllic Caribbean island of St. Barts. "I love these vacation babes @laurenz422 @stepheniepearson," she wrote on the snap that shows the crystal clear water behind her and her crew.

In the photo, Jessica rocks a black one-piece and a net cover-up. The beachy ensemble stops at the top of her thighs, showing off legs that even a marathon runner would be envious of. The rest of her outfit, as usual, is stylish and perfect.

Celebrating her birthday in St. Barths, Jess simply posted an image of herself in a Native American headdress on July 10, simply captioning it, "35," her age. Jessica is obviously aging gracefully.

Jessica is believed to have flown 30 of her closest friends to celebrate her 35th birthday with her (our invitation must have gotten lost in the mail.)

Earlier this year, she spoke to InStyle about her rigorous fitness routines, which helped her drop 70 pounds!

"Having two kids back-to-back was hard on my body," the mommy of two said, adding that she doesn't think she'll have another. "But if I do have more, I wouldn't want them to read this and think they weren't wanted!"

As for her fitness, she focuses on that after she puts the kiddos to bed.

"I work out five days a week: three days with a trainer, doing a mix of strength training and cardio, and then I do cardio on my own the other two days,"she said. "Somehow I make it work, but I've slowed down since my wedding. I worked really hard because I wanted to appreciate being in a wedding gown again. I wanted to enjoy it like I did the first time. But I didn't have a weight goal; I just wanted to look healthy."

#LegDay is everyday for Jessica.