There are oodles of articles that list out the benefits of high intensity exercise from various studies. We are going to give a quick summary. Imagine the infomercial we will run. The announcer will list:
Burns calories efficiently. Short bursts of exercise raise the heart rate quickly, so an intense workout does not need to be as long as a slow cardio workout to burn the same number of calories.
Endurance. Studies show that HIIT is as effective or even more effective at raising a person's VO2 Max which is the gold standard measure of endurance. VO2 Max is measurement of your body's ability to process oxygen. Scientists have done studies to show that HIIT improves the function and quantity of mitochondria in the body. Mitochondria help the body process oxygen.
Heart Health. HIIT has been shown to reduce the risk of heart disease in multiple studies. Our own cardio consultant at the Lown Sports Cardiology Center in Boston showed us images of patients who reversed their heart disease with HIIT programs.
Burns Fat. Studies show that HIIT burns fat.
Lowers Blood Pressure, Cholesterol and Blood Sugar. reducing the risk of heart disease and diabetes.
Improves brain function and plasticity.
NOTE: Many of the claims above can be made about any form of exercise vs not doing exercise. Some studies do show superior benefits to do doing HIIT vs steady state exercise, but it's best to do a combination of both.