But first, they had to take a selfie!
Kourtney Kardashian and Kylie Jenner hit the gym together on Saturday, but not without sharing some selfies, of course!
The Keeping Up With the Kardashians stars took to Instagram to show off their toned tummies in cropped work out tops and high-waisted athletic pants.
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Kardashian, 36, has apparently been trying to get her youngest sister to join her in the gym for months.
"I've been trying to get her to workout with me for six months...today was my lucky day," she captioned a full-length shot of the two posing in the mirror.
"First workout with @kourtneykardash this lady has been working hard!" Kylie, 18, captioned her pic, showing them lying on their workout mats.
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Kardashian has been all about getting fit, as proven by her frequent social media posts as of late.
"I'm so proud of these guys," she captioned a pic of several pairs of running shoes lined up on a fur rug.
The mom of three also showed off the results of her gym sessions, in an all-black ab-tastic ensemble.
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"I needed a good workout today," Kardashian captioned another snap.
Jenner, meanwhile, has felt fit and festive this week. The 18-year-old reality TV star shared a throwback clip of her completely freaking out over a Christmas gift, reminding us all that she was once just an innocent kid.
"I hope I get this excited this Christmas lol," she captioned the video on Saturday.
Earlier this month, Kylie got in the holiday spirit by decking out her Ferrari -- a gift that was given to her by Tyga for her 18th birthday -- with reindeer ears and a red nose. Watch the video below to hear more.