If you're craving a quick cardio workout, let me introduce you to your new best friend: YouTube. These seven videos (all 100 percent free) are guaranteed to pump up your heart rate and get you sweating, all in just 10 minutes or less. Even better? Each one requires no equipment but your own body (and maybe a mat or some comfy floor), so you can get sweating from the comfort of your own living room, dorm room, bedroom, garage - you get the picture. Just click play and grab a towel to mop yourself up afterwards.