• Share
  • Tweet
  • Share
Kourtney Kardashian, Kylie Jenner, Gym

Instagram

Khloe Kardashian isn't the only one hitting the gym hard!

Sister and mother of three Kourtney Kardashian, 36, has been showcasing her own shrinking figure over the past year and recently posted a new workout selfie, in which she sports a sexy, strappy cut-out crop top and black tights. Joining her is Kylie Jenner, 18, who showcased her trim figure in a gray sports bra and cropped tights...and who has apparently been reluctant to join her sister on her fitness fitness.

"I've been trying to get her to workout with me for six months...today was my lucky day (sic)," Kourtney wrote on Instagram on Saturday alongside a mirror selfie of herself with Kylie, who took the photo.

Kourtney Kardashian, Kylie Jenner, Gym

Instagram

Kylie also shared photo of the sisters' bonding time, showing the two working out while laying on their sides on mats.

"First workout with @kourtneykardash this lady has been working hard!" she wrote.

#throwback I hope I get this excited this Christmas lol

A video posted by King Kylie (@kyliejenner) on

Also on Saturday, Kylie shared a throwback Keeping Up With the Kardashians clip showing herself several years ago, watching a home video of herself as a child, freaking out over Christmas gifts.

Watch Keeping Up With the Kardashians on Sundays at 9/8c on E!