Great bodies like these don't just HAPPEN!

Justin Bieber and Hailey Baldwin work their BUTTS off working out! The pair didn't even take Memorial Day holiday off -- they hiked it to the gym for a sweaty workout and it's definitely paying off ... check out Hailey's long, slim stems in yoga pants as she headed to the gym and check Justin's shirtless selfie from the studio yesterday. #ThirstTrap!

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Studio vibes.. with my studio chicka ..

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