Short bursts of exercise tell your body that storing energy as fat is inefficient, since you never exercise long enough to utilise the fat during each session. Carbohydrates, which are stored in muscle rather than fat, burn energy at high rates. Exercising for short periods will use these carbs and burn much more fat after exercising while you replenish the carbs. Short interval exercise maximises fat ‘after burn’.
Researchers at Laval University in Quebec divided participants into two groups: long-duration and repeated short-duration exercisers. They had the long-duration group cycle 45 minutes without interruption. The short-term interval group cycled in numerous short bursts of 15 – 90 seconds, while resting in between. The long duration group burned twice as many calories, so you would assume they would burn more fat.
However, when the researchers recorded their body composition measurements, the interval group showed that they lost the most fat. In fact, the interval group lost 9 times more fat than the endurance group for every calorie burned. Doesn’t this defy the laws of physics? No, it just illustrates that exercise continues to affect your metabolism after you stop. The short bursts stimulated a greater after burn.
In addition, short duration bursts produce many other desirable results for your metabolic health:

•    Improves maximal cardiac outputs

?•    Promotes the development of quicker cardiac adjustments to changes in demand

•    Helps you lose body fat with as little as 10 minutes per day

•    Achieves ‘higher peak stroke volumes during overload.’ (Your peak stroke volume is the maximum amount of blood your heart can pump per beat when maximally challenged)

?•    Improves cholesterol levels

•    Provides an anti-ageing benefit by raising testosterone levels, which fights against memory loss, accumulation of fat, low libido, sexual dysfunction, and loss of strength and bone

•    Helps you lose weight by burning much more fat after you stop exercising

… and you’ll be able to get these benefits with much less of your time – no need to spend hours at the gym!
So the recent ‘cardio craze’ was a mistake because it produces an unnatural challenge and failed to take into account your body’s adaptive responses like shrinking internal organs, shrinking and weakening muscles, decreased cardiac reserve capacity and an increased dependency on body fat for energy.