A workout is a little like a remix: take the good part, isolate it, tweak and discover something new in the process. And on a less metaphorical level, the energy-boosted peaks of a great remix make for a perfect workout companion. Just take this set of pop, hip-hop, dance and rock reworks as a case in point. Our editors switch up picks now and then, so if you hear something you like, add it to your library.