This piece from Dr. Mercola is long, but there's are many nuggets contained therein.
After monitoring the Japanese speed skating team in the early 90's, Dr. Tabata noticed that extremely hard but intermittent exercise appeared to be at least as effective as standard workouts that require several hours a week. The training protocol he came up with as a result requires a mere four minutes, four times a week. The caveat? Extremei ntensity.
Dr. Tabata's HIIT protocol calls for just 20 seconds of all-out drop-dead effort, followed by a mere 10 seconds of rest. This intense cycle is repeated eight times. According to Dr. Tabata:
"All-out effort at 170 percent of your VO2 max is the criterion of the protocol. If you feel OK afterwards you've not done it properly. The first three repetitions will feel easy but the last two will feel impossibly hard. In the original plan the aim was to get to eight, but some only lasted six or seven."
When performed four times per week for six weeks, participants in one experiment increased their anaerobic capacity by 28 percent, and their VO2 max (an indicator of cardiovascular health) and maximal aerobic power by 15 percent. This is in contrast to the control group, who performed an hour of steady cardiovascular exercise on a stationary bike five times a week. These participants improved their VO2 max by just 10 percent, and their regimen had no effect on their anaerobic capacity.
Dr. Tabata also has forthcoming research findings showing that his protocol reduces your risk of diabetes, which other HIIT studies have already suggested. And, according to the featured article:
"Another soon-to-be-published finding, which Tabata describes as 'rather significant,' shows that the Tabata protocol burns an extra 150 calories in the 12 hours after exercise, even at rest, due to the effect of excess post-exercise oxygen consumption. So while it is used by most people to get fit – or by fit people to get even fitter – it also burns fat."
Dr. Mercola offers a very thorough review of the benefits of hard, short workouts. But the best advice is - just do it. Short and intense builds muscle, rewards correct body position and mechanics and helps one to feel those things as applied to generating force. Forget the 30 minutes on a treadmill five days a week - try 10 minutes of warm up workout and cool down instead.
If you like long slow distance, have at it, but please don't labor under the mis-understanding that short, hard exercise is bad for you; it's anything but.