It tickles me when fitness professionals refer to high-intensity exercise as "fat burning."
High intensity exercise burns calories; the fat is burned once the workout is over and the athlete partakes in a healthy nutrition plan that is very low on sugar and involves the proper calorie intake.
HIIT(high intensity interval training) is a wildly popular way to exercise right now, and rightfully so. It's amazing benefits include boosting metabolic rate, high caloric burn, post workout after burn, and a serious endorphin high if you do it right. However, HIIT does not use body fat for energy, it uses carbohydrates, glycogen in the muscle, and ATP (adenosine triphosphate). Here is a brief explanation of why HIIT should not be referred to as "fat burning."
I’m going to be quick and try to use words that are simple as this is a science and the terminology can get kind of ridiculous.
High Intensity Interval Training (HIIT) is intense, sometimes 100% given bouts of effort followed by short recovery periods. It gets the heart rate up and burns a high amount of calories in a short period of time.
Now the body has three main energy systems and manipulating these systems during sessions is a big part of my training style. They are phosphagen, glycolysis, and oxidative. At any given time all three systems are active but the contribution of each system during training depends on the intensity and duration of the activity.
The best example of the phosphagen system at work is watching a sprinter. OR during a boxing match when a boxer has his opponent on the ropes. The opponent is obviously hurt so the boxer gives everything he has in an effort to drop his opponent. There is no strategy here, just all out effort. This is how the “working” part of HIIT should be performed; with all out effort. Now you can only do this for a short period of time, and the body cannot rely on oxygen so it is therefore “anaerobic.” Now out of all the macronutrients ONLY CARBOHYDRATES can be used for energy if there is not involvement of oxygen. Your body prefers carbs as source of energy because they break down 30-40% faster than fat. Have you ever tried doing HIIT on an empty stomach? Doesn’t work out too well.
Glycolysis is the breakdown of carbs- whether it be glycogen in the muscle or sugar in the blood. For the most part this is the energy system we are using when we work out. We’re giving intense effort but it is not 100%, and most of us don’t train for hours so it’s not prolonged exercise.
Now the oxidative system is where FAT is burned (used for energy). Lower intensity exercise, steady state work for a prolonged period of time. This is when the body shifts from using carbs for energy to using fats and protein. Yes protein too, that’s why it’s not ideal for muscle building and preservation.
Dr. Len Kravitz, Ph.D. is a well respected exercise physiologist in the fitness industry. He performed a lab experiment that gave these results: 66% effort over X amount of time burned 219 calories, 35 Fat cals and 184 carb cals. 74% effort over X amount of time burned 249 calories, 30 Fat cals and 219 carb cals. 83% over X amount of time burned 275 calories, 22 Fat cals and 253 carb cals.
So basically what I’m saying is HIIT burns a lot of calories and you will burn fat but it’s not until AFTER the actual exercising (E.P.O.C.), not during. And I’m annoyed with people calling HIIT fat burning, ESPECIALLY exercise professionals. They should know better. But we all know that all fitness pros are not created equal.
Ready. Set. HIIT it!!!
