VIDEO : Kylie Jenner & Kourtney Kardashian Spend Some Time Together At The Gym

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