Interval training produces a greater response from the body than steady state cardiovascular exercise. The more intense the exercise is for your body, the greater response your body will have to it. In other words, you will get better results -faster with intervals than with boring traditional steady state exercise.

 Here is more evidence, as reported by the NY Times, that sprinting should be part of your muscle arsenal.

“More and more, professional organizations are recommending interval training during rehabilitation from diseases like chronic obstructive pulmonary disease, peripheral artery disease and cardiovascular disease,'’ said Maureen MacDonald, academic adviser and an associate professor in the department of kinesiology. “Our research certainly provides evidence that this type of exercise training is as effective as traditional moderate-intensity training. We wouldn’t be surprised to see more rehabilitation programs adopt this method of training since it is often better tolerated in diseased populations”.

What's interesting is how interval sprinting is often "better tolerated" in diseased populations. I totally agree that it's better tolerated because it is a shorter workout, it is more interesting, challenging, and engaging. This stimulating way to workout is exciting and elicits a greater response from your body and mind.

Here is Conditioning Research on the same topic, it's nice to see we are on the same page.