The so-called fat burning zone occurs when exercise is primarily fueled by body fat. It’s a belief that is based in exercise physiology, but one that is now considered a myth because it overlooks a key factor: total calories burned.
To understand how low and high intensity exercise influences weight loss, it helps to first understand how the body uses fuel during exercise.
- Exercise is fueled by a mix of fat and carbohydrates. Exercise intensity changes the amount of fat and carbohydrate used by the body.
- When exercise intensity is low, the body uses a greater percentage of fat to fuel muscles. As intensity increases, the body increases its use of carbohydrates. The greater the increase in exercise intensity, the greater the dependence on carbohydrates for fuel.
While the calories burned during low intensity exercise are primarily sourced from body fat, higher intensity exercise can burn more stored fat in the same amount of time because the total amount of calories burned is greater. The table below provides an example.
|Exercise Intensity||Calories Burned*||Fat %||Carb %||Fat Calories Burned|
|Moderate to Vigorous||555||35||65||194|
*Energy expenditure (calories) based on a 45-minute workout with constant intensity
Regardless of how many calories are burned from fat, the key to weight loss is to burn more total calories than you consume. This makes higher intensity exercise a more effective option for weight loss because it not only burns more calories from fat, but it burns more total calories per exercise session.
Lower intensity exercise has its place in your workout plan, especially if you are a beginner. But don’t keep from pushing harder because you think a lower intensity workout will create a magic fat burning zone. As you become fit, start incorporating higher intensity bouts into your workouts to maximize your weight loss efforts.