High intensity interval training is undoubtedly one of the most talked about weight loss tips of the 21st century. But if you are unsure why so many gym lovers are jumping on board the HIIT train, you're about to find out the main reasons.

This isn't a fad or a passing trend, so today you will learn why it's becoming such a popular choice.

Although it has only recently crossed over in to mainstream society, HIIT has been used for nearly three decades. It was previously widely believed that cardiovascular activity performed over a long distance at a steady pace was better for both endurance and fat loss. However, recent studies have blown these old theories out of the water.

To go back to the roots of HIIT, you need to look at the two studies which brought it into the public eye. The first of which dates all the way back to 1985. Initially designed to test if exercises helped speed the metabolism, scientists noticed that most of the weight loss results were from individuals working harder in the gym. A further study confirmed this, with three weekly HIIT sessions outperforming five regular cardio workouts for fat loss, despite those workouts being twice as long.

From there, interest in this subject was high and research was being carried out almost every single year. Many athletes adopted it to their own training regime. Sprinters and swimmers were particular fans at this point.

A Canadian study in 2001 then produced the most thorough research on the subject to date. It detailed that a group of exercises not only lost more body fat while working out for less time and less often, they also increased the body's fat burning enzyme HADH. This finding was initially quite shocking, because HIIT is known to use carbohydrates as the source of fuel in the gym, not fat. This increase in HADH occurred because high intensity activity actually causes the body to switch to using fat for fuel in the period following a workout. Furthermore, this period can last a shocking 14 hours in length. []

By increasing the production of HADH after each workout had finished, the body is able to switch to using fat for fuel over the course of the next 12-14 hours.

The biggest finding of the whole test, and the one which will undoubtedly interest the most people reading this review, is the fact that researchers confirmed that one calorie used during a HIIT workout shed almost six times the fat of one calorie used during a steady state workout. That's because the body continues to burn calories after the session as a result of keeping the intensity level quite high.

These startling results have since been backed up by many further studies. In fact, over the last few years this training method has crept it's way into many mainstream gyms around the world and it now appears to have earned it's place among proven fitness techniques.

Like all new fitness concepts, high intensity interval training has recently made it's appearance in the mainstream. This can lead to some labeling it as a passing fad but, having seen the mounting evidence behind it's effectiveness, you now realize that HIIT can become one of the most productive weight loss tips for those who are prepared to learn a little bit about it before jumping in.