When most people hear the word cardio, they probably picture a treadmill, elliptical, stationary bike, or a long run. When they hear conditioning, they may picture an athlete doing sprints, sled pushes, or a brutal circuit. The terms are often used interchangeably, but cardio and conditioning aren't necessarily the same thing. Both are important. Both can improve fitness. But they serve slightly different purposes—and understanding the difference can help you build a more eff