The concept that longer lower intensity cardio sessions are better for weight loss has been around for quite some time and is often referred to as working out in the fat burning zone. This idea is a myth and a misinterpretation of the body’s energy systems. The average person burns a mix of 50% fat and 50% carbs when at rest (well trained individuals burn 70% fat and 30% carbs). When a person begins to exercise the mix changes and carbs begin to take over energy production.

The higher the intensity of your workout the less fat you burn. This is your body’s way of delivering oxygen to exercising muscles faster. It sounds reasonable to think that if you exercise at a lower intensity and burn more fat you will lose more weight but contrary to popular belief that is not the case. The best way to lose weight is by burning more calories than you consume and exercising at a higher intensity tends to burn more calories.

Here’s an example; a 130lb woman who performs 30 minutes of cardio at 60-65% of her maximum heart rate burns 146 calories and 73 total fat calories while a 130lb woman who performs 30 minutes of cardio at 80-85% of her maximum target heart rate burns 206 calories and 82 total fat calories. As you can see the second woman is burning the most calories, which is what really matters when it comes to weight loss, but she is also burning more fat calories. If both women eat a similar diet and they are burning more calories than they are consuming then the second woman will lose weight faster.


Here´s how to calculate your target heart rate range for higher intensity exercise:
220 - your age = max HR
max HR x .70 = lower end of your range
max HR x .85 = upper end of your range
For example, if you´re 30 years old:
220 - 30 = 190
190 x .70 = 133
190 x .85 = 161
You can also use ratings of perceived exertion to determine the intensity of your workout, with a 5 being a low intensity workout and a 10 being a really high intensity workout.

If you find that you have a tough time staying between 70-80% of your maximum heart rate you can work up to it by trying an interval training workout which switches back and forth from low to high intensity. Most cardio machines have an interval program or you can use a watch to switch back and forth every 1-2 minutes. You can also try switching out one of your longer lower intensity workouts for a 20 minute higher intensity workout every week until you start to build up some stamina and then you can mix it up as much as you like. It’s important to continue to do both types of cardio workouts so that your body doesn’t get accustomed to either one. This way you burn as many calories as possible while avoiding a plateau, boredom, and injuries.

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