A year later, a research review in the Scandinavian Journal of Medicine and Science in Sports reported that incorporating HIIT into a training program could improve the exercise performance of well-trained adults by 2% to 4% in less than one month.
Interval training can also be good for people who don't engage in any anaerobic exercises that require short bursts of strength and power, such as weightlifting. I spend a lot of time lifting weights, so I'm already getting plenty of anaerobic exercise, but if all you ever do is aerobic activity, then HIIT would allow you to train the larger "fast-twitch" muscle fibers that can increase muscle mass and improve your physique.
If you need convincing, remember that your typical sprinter looks like the Old Spice guy, whereas most marathoners resemble Sheldon from "The Big Bang Theory." It's important to note, however, that HIIT won't build as much muscle as intense weightlifting.
If you decide to give it a try, keep in mind that the National Strength and Conditioning Assn. (to which I belong) says that interval training is not for the out-of-shape and should be used sparingly because of its punishing intensity. I totally agree with this one. So does my wife, who is tired of hearing me groan.