Don't Make This Mistake on The Treadmill: The Myth of the Fat Burning Zone

Knowing your max heart rate, monitoring your heart rate during exercise and working in heart rate zones can be a great way to gauge intensity during your workouts. When you are trying to lose fat, it can be a little confusing to determine the correct heart rate zone to meet your goals. There is a lot of misinformation circulating and treadmill manufacturers add to this confusion.

We've all seen the chart on the treadmill at the gym. It says something like this:

Fat Burning Zone 60-70% of max heart rate

Cardio zone 70-80%  of max heart rate

Anaerobic zone 80-90% of max heart rate

Max 90-100% of max heart rate

It sounds great and easy. Want to lose fat? Work in the low intensity fat burning zone to burn more fat, right? Not so fast.

When you workout your body uses mostly fat or carbs (glycogen stores) as the energy source. While working at 70% of your max heart rate it's true that the overall percentage of fat utilized is higher in this low intensity heart rate zone. However you will burn a higher number of calories while working at a higher intensity.

What matters is the total amount of calories you burn, not the percentage that comes from fat. If you exercise at a lower intensity, a higher percentage of energy may come from fat, but this still will be a smaller number of overall calories.

If you increase your workout intensity, you will burn more total calories and therefore more fat calories.

Here's an example: At 60% max HR your calorie burn will be approx. 66% fat and 34% carbs. If you walk for 20 minutes at 60% max HR you may burn 100 total calories (rounded for easy math) and that would equal 66 fat calories. If you increase your workout intensity to 80% of your max HR, in the same 20 minutes you may burn 200 total calories, but the percentage that comes from fat drops to only 50%.

Max heart rate          Total Calories          %Fat         Fat Calories

60%                            100                         66%           66

80%                            200                        50%           100

You burned 100 fat calories at 80% max HR which is more than the 66 fat calories you burned at 70% max HR. You can see that at the higher intensity you burned a smaller percentage of fat, but still a larger amount of fat calories and overall calories. 

In the end it’s not about what type of fuel you burn while you workout, it’s about overall calorie expenditure to lose fat. 

The best method to lose fat is to increase your intensity to burn more overall calories. You can burn enough calories for fat loss at a lower intensity, you just need to do it for a much longer duration. A more efficient way to lose fat is to increase intensity. 

If you are unable to maintain a higher intensity workout, it is best to do low intensity while you build your fitness base. It's important to note that the low intensity heart rate zone has its place. 

Besides being great for active recovery in between hard workouts, It is the perfect heart rate zone for people new to exercising, returning after an extended break or people with significant amount of weight to lose to safely build a cardio base. Once you can safely maintain 30-45 minutes of low intensity work 3-4 times a week, you will likely be ready to graduate to higher intensity exercise.

It is a mistake to work on the treadmill at a lower intensity than your fitness level allows because you believe that this is going to burn more fat. Get that heart rate up to see incredible results!

Are you confused by the heart rate zones and how to calculate your own max heart rate? Check out this blog post to clear it all up for you in my Running A-Z series: H is for heart rate. 

Like this post? Please consider sharing.