4 High-Performance Cardio Workouts

Take your cardio training to the next level with these athlete-recommended routines.Some people are satisfied simply slogging through their cardio, counting the calories burned, and hopping off the machine. Others want more. They want conditioning that makes their engines bigger and their entire bodies more capable.
But if you're looking to take your cardio to the next level, you need to find workouts that push you to your limit. These four routines definitely will. They're from RSP's super-fit