to be clear, traditional cardio activities DO NOT build muscle. In fact, they do the exact opposite. I didn't say exercises, I said activities. Sprinting will

to be clear, traditional cardio activities DO NOT build muscle. In fact, they do the exact opposite. I didn't say exercises, I said activities. Sprinting will actually build muscle, jogging 20 miles will not. It is a difference in how your body adapts to the stimulus. So, with that in mind, no, cardio typically is not a good choice for people with what 80% of people are hoping to achieve. Put plainly, the time/reward tradeoff is just too low. Sprint, bike sprint, row, swimming, they are all better than the elliptical, typical running and the like. http://www.drkehres.com/2009/06/sprinters-versus-marathon-runners.html http://www.drkehres.com/2009/06/sprinters-versus-marathon-ru... If you are a world class marathoner and are running 6 minute miles for a marathon, you will probably have some muscle and look pretty lean. That being said, 99% of the world is not this and are basically working out for hours with very, very little benefit to the time. However, even a recreational sprinter is going to see huge benefits from sprinting in both muscle building and fat reduction.