The Myth of a “Fat Burning Zone” for Exercise
Graphs such as this one have caused many to believe in the idea of a “fat burning zone”. The fact is, all exercise will burn calories and therefore fat. The reason that low to moderate intensity exercise is recommended is because people are able to exercise for a longer time (and therefore, burn more calories).
Graphs similar to the one above are frequently used to describe the concept of a “fat burning” zone for exercise. While the graph provides a nice conceptual model of the heart rates that are suitable for different goals, it is often misinterpreted and used incorrectly. For example, many individuals interpret this graph to suggest that there is an optimal “fat burning” zone that is best for burning fat. This myth is based on the fact that the body preferentially uses fat as a fuel source during low to moderate intensities. While this is true “metabolically”, it does not influence the degree of overall weight or fat loss from exercise. All of the bodies fuel sources are readily inter-convertible. Thus, in terms of weight control, it doesn’t matter which fuel source is used as long as calories are expended.
It is still true that moderate intensity activity is the best choice for weight loss but the reason is that it is possible to perform a larger volume of this activity and therefore, burn more total calories. However, if you are short on time, vigorous activity can be more effective since you can burn more total calories in the same time.