What takes up just three minutes of your time, has you in crunch mode, and needs no equipment at all? This core workout shared by fitness YouTuber Maddie Lymburner (aka MadFit)! The choreographed, follow-along session set to Justin Bieber's "Hold On" features mountain climbers to the beat and moves that require a lot of core control such as scissors on your elbows and a variation of windshield wipers. You'll crunch, crunch some more, and maybe even smile along the way. Check it out in full above, and if you're looking for a lower-ab workout from a certified trainer, check out this five-move session by Nicci Robinson (it's hot off the press!).