You have seen the little stickers on the machines at your local gym. Those little graphs that show where your target heart rate should be in order to improve your cardio system or to blast fat away.
My favourite part of the diagram is the fat burning zone. The little figures slaving away annihilating their fat while they keep their heart rate way down in the comfort zone – you know it – where you can still chat away and barely a bead of sweat drips down your brow?
This is a series on busting up exercise myths and as I am a stickler for being factual – I have to confess something.
The fat burning zone isn’t totally a myth.
Don’t go skipping merrily to the elliptical to put in a half ass 30 min watching Cheers reruns. There are a few caveats we should discuss.
First – the science of the matter is that at 60% of your max heart rate you typically will be able to turn to your fat stores as a fuel supply. Now the preferred source of energy in your body is glycogen (this is energy that is stored in your muscles and liver – its sugar – your body stores carbohydrate in these areas in a form that is readily used for energy) and it will typically use this first. And you are never 100% using energy from one source. So in the fat burning zone you are simply using a higher percentage of fat energy than you are from other sources. So even at higher intensities you are still burning fat, just a smaller percentage.
So even when you are training at lower intensities your body will go to the stored glycogen first before it ever dips into your fat storage. This simply means that you have to burn through all that first and then you can get into the good fat burning fun. While no one really knows and there is going to obviously be variance between individuals, it is believed that it takes women between 45 and 60 minutes to switch into fat burning metabolism and this time is shorter for men. Again, there is a ton of variance here and these numbers are based on using low intensity exercise for the entire exercise session (more on that later).
What this means then is that the first 45 minute you ride that elliptical diligently following the happy little diagrams to fat burning bliss, you are not yet tapping into your fat stores. No, you have to get through the first 45-60 minutes and then keep on going to burn straight into your fat.
The truth is this – you want to burn fat and get a leaner physique. And that is fine. But let’s look at the most efficient way to get there.
Yes, you can use the fat burning zone to burn of excess body fat but it is very inefficient. To burn a significant amount of calories just from fat you are going to have to do your 45 min of low intensity exercise first and then another 45 to 60 minutes of fat burning zone low intensity exercise. And to burn a significant amount of calories at this intensity you had best be prepared to do this 6 or 7 days a week.
Sounds like fun?
No, it isn’t. It isn’t at all!
Instead it is most efficient to workout at higher intensities and burn off a larger number of calories. While the percentage of those calories from fat will be lower, the greater number of overall calories will mean that the same number of sticky little fat cells get metabolised away into useful energy. Not to mention that high intensity exercise has a host of other benefits that come along with it (like better cardiovascular health, improved hormone response, and more strength) that boring little low intensity exercise just can’t do.
So while the fat burning zone does technically exist, it really isn’t practical for most people and it is the least effective way to change your body the way you want to!