Compared the physique of a world-class distance runner with that of a world-class sprinter? The sprinter's body resembles that of a Greek Adonis, with chiseled arms and powerful quads, while the skinny-fat distance runner makes THIN SKINNY LOOK...The answer if the type of training. In sprinting the sprinter has to do all out for few seconds and rest for few minutes, where as the long distance runner run at low pace and don't take rest during any interval. .
HIIT is a training idea in which low to moderate intensity intervals are alternated with high intensity intervals.
HIIT can be applied to running or to exercises such as squatting. HIIT is considered to be much more effective than normal cardio because the intensity is higher and you are able to increase both your aerobic and anaerobic endurance while burning more fat than ever before.
Excessive aerobic activity can decrease testosterone levels, increase cortisol production, weaken the immune system, handicap strength gains, and halt any hope of hypertrophy. But this doesn't mean you can't maximize muscle mass and strength gains while conditioning. It just means you need to be smart about your cardio. And choose some HIIT schedules.
"In research, HIIT has been shown to burn adipose tissue more effectively than low-intensity exercise - up to 50% more efficiently." It has also been shown to speed up your metabolism which helps you burn more calories throughout the day.
HIIT improves both energy systems for ENDURANCE