A hot and sweaty Justin Bieber always makes us hot and sweaty! Somehow, though, Bieber prodigy Madison Beer kept her cool as she "hiked" with the world's sexiest pop star. Beer didn't realize how seriously Biebs takes his hikes -- he trail runs but she wasn't prepared in her fringed Converse high tops and Chanel backpack.

Justin didn't care, though -- he ran ahead, keeping a pretty fast pace. When we asked Madison if she has trouble keeping up, she concurred! And by the way ... could these two be hooking up???