Energy Expenditure and The Fat Burning Zone Myth

As a fitness professional I am constantly being reminded of one of my least favorite exercise myths: The Fat Burning Zone. The fat burning zone recommends long duration, moderate exercise for the best “fat burning” workout. Although this zone does technically exist, the specifics have become lost in translation.

When looking at a traditional piece of cardiovascular equipment, such as an elliptical machine, the fat burning zone is typically listed as 65% of the individual’s maximal heart rate. At this heart rate you will be burning a greater percentage of calories from fat, not a greater number of total calories from fat. This is a key detail to note when you are planning your workouts. Although you may be burning a greater percentage of your calories from fat, the total number of calories burned is lower than if you had been exercising at a higher work rate. This then begs the question, what should your heart rate be during exercise? The answer to this question is dependent on your individual goals.

For the previously stated purpose of fat loss, the long slow cardiovascular exercise is not the best approach. Utilizing techniques such as interval training to reach a higher intensity heart rate, ≈70-90%, will have an end result of more calories burned. In the world of weight loss, burning more calories is the ultimate goal. An added benefit being that higher intensity workouts can be preformed for a shorter amount of total time, which makes it easier to find time for your workouts and stick to your program. It is important to note, however, that high intensity workouts are not recommended seven days per week. Long duration, moderate exercise can act as a recovery workout between your high intensity days. It can also be a great stepping stone for beginners who are just becoming involved with exercise.

How to calculate your target heart rate:

Before you begin, you will need to know two numbers, your resting heart rate and your maximum heart rate. Maximal heart rate may be discovered through testing, or with one of the many age-predicted maximal heart rate equations such as 220-age. Resting heart rate can be measure after the body has been at rest for 10-15 minutes, preferably in the morning without the effects of stimulants such as caffeine.

There are two types of percentages used for prescribing heart rates. Percentage of max heart rate and percentage of heart rate reserve. Determining the percentage of heart rate max is fairly straight forward; multiply your desired intensity by your maximal heart rate. To determine your percentage of heart rate reserve, you will use a few more steps. First, calculate your heart rate reserve by subtracting your resting heart rate from your maximal heart rate. Next, simply multiply the heart rate reserve by your desired exercise intensity, then add your resting heart rate back in.

You are now ready to begin training based on target heart rate zones!


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