Is the Fat-Burning Zone a myth?
The “fat-burning zone” chart on exercise equipment probably isn’t what you think it is. Find out what it really means.

That "fat-burning zone" chart on exercise equipment might not be what you think it is.  Keeping your heart rate within a certain range based on a chart is a bit misleading.  The first thing to consider is that people's heart rates differ, which makes it difficult to generalize recommendations on a fixed chart.  Second, during exercise your body uses both fats and carbohydrates, protein is an energy source too, but it's only used in very small amounts.  However, the proportion of each macronutrient you need varies depending on the intensity of the exercise.

Lower-intensity exercises (that is, with lower heart rates) performed for longer durations, 30 minutes or more, mostly rely on fat for energy. What that means is that in the "fat burning zone" for this level of exercise, your body is using a higher proportion of fat for energy, but you are not necessarily burning more fat.  Your body actually utilizes the most fat during rest.  So in theory, the best "fat-burning zone" is lounging on your couch watching your favorite movie.

The best way to burn more fat is to do more high-intensity exercises.  You might not be exercising as long, but you'll burn more fat due to the higher overall energy, caloric, expenditure.  Interval training is a great way to boost the intensity of your workout, and you get that afterburn effect.  Fitness level also is a factor.  Fitter people's bodies tend to utilize more fats than carbohydrates.

If you're training for endurance activities, such as long distance races, the "fat-burning zone" on exercise machines might be the "right zone" for you.  But to burn even more fat, ultimately you need to burn more calories overall.  High-intensity workouts are a challenging and efficient way to help reach that goal.