Although this is a simplified version, every thing you consume gets broken down and utilized into three main subgroups: Carbohydrates, fats, and proteins. The first thing I’d like you to notice in the table above is the Fat to Carbohydrate percentage used at ½ intensity (lines 1+2 in blue). The energy consumption equates equally to about 50%-50% in energy usage between fat and carbohydrate while engaged in slower exercise.
The next thing I’d like to compare is the percentage of Fat consumed at ¾ intensity (fast) to the percentage of Fat used at ½ intensity (slow). You can see that the percentage of fat burned at ½ intensity (slow) is 10% greater than the 40 % of fat burned at ¾ intensity (fast). A conclusion that could be made from this is that one burns more fat at lower exercise intensities. Now let’s look a little closer.
Next, if you look at the total calories used for each intensity you’ll notice that more calories are used in all components of the ¾ intensity (fast). Your body requires more energy and more calories to perform more difficult work. Even though you burn a higher percentage of fat to carbohydrate calories at low intensity, the absolute value of fat calories burned at the high intensity is greater. What does all this mean?
If your goal is to loose fat, then the high intensity training is what will lean out the body and give you that toned look. If you at first have trouble maintaining hard intensities, try doing some interval training where you perform periods of alternating fast and slow intensities. Last, if you don’t feel comfortable pushing yourself hard, just remember every intensity burns the fat.. but you may have to put in more time at slow intensities to get the same results.