Most people who have been in a gym and used a piece of standard cardio equipment have seen the diagram that shows the target heart rate for the "fat burning zone." What is the "fat burning zone?" This is the intensity where you would be burning the highest percentage of your calories as fat. This is a bit misleading since the highest percent of calories burned as fat is at rest. The "fat burning zone" is typically prescribed at 50-60% of your maximum aerobic capacity (aka VO2max), which generally equals 60-70% of your maximum heart rate. As a comparison, training for cardiovascular fitness is usually prescribed at 65-85% of aerobic capacity or 75-95% of maximum heart rate.

This sounds great for people looking to lose weight; "if I train at a lower intensity it will be easier and I'll lose more fat." Who wouldn't want that? The problem comes from the use of percentages. All this information is correct; you burn a higher percentage of fat at the "fat burning zone" as you do for when you are training for cardiovascular fitness. However, you aren't burning more fat overall. As an example, if one was to exercise at 50% of their aerobic capacity they would burn about 50% of their calories as fat, which would equal to approximately 480 calories over an hour. With 50% as fat one would have burned 240 calories of fat. Not too shabby. Now if the same person exercised at 70% of their aerobic capacity, 40% of the calories would be burned as fat. Over the same hour 660 total calories and 265 calories of fat will have been burned. This shows how even when you exercise outside of the "fat burning zone" you can burn more fat overall.

In addition, more overall calories are burned which is the main determinate of weight loss. Another aspect to consider is that endurance training can increase ones percentage of fat usage at the same intensity. So the harder (up to a point) you train the more your body will get used to using fat as fuel. The intensity does need to stay low enough that you can do the exercise for a significant amount of time, and the exercise session needs to last longer than 20min as that is how long lypolisis (breakdown of fat) takes to "kick in."

The best recommendation is to go as hard as you can for as long as you can. If you have 25min, goes as hard as you can for that time period. If you have 45min go as hard as you can for that time period, which might be a little less intense than if you have only 25min. This way you will burn the most overall calories and the most fat calories.

Learn more about this author, Shane Ferth.
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