Is the Fat Burning Zone a Myth?

There are many things that we accept to be true when it comes to losing weight and often we don’t question these things as much as we should. Take for instance the idea of a ‘fat burning zone’. Many of us will have been designing our workouts around this concept and some personal trainers will tell you this is a good idea – but if you look a little deeper you may find it’s not as sure a thing as you previously believed. Let’s take a closer look and see if there really is a ‘fat burning zone’ or if it is just a myth.

The Idea

The general idea here is that there is a fat burning zone which is the optimum heart rate for losing the most weight. Usually it is agreed that this should be somewhere around 70-75% of your MHR (Maximum Heart Rate) and the reasoning behind this is sound.

When you exercise, your body needs to find energy to help you keep going. To do this, it can look to the muscles, the blood stream or your fat stores.

When you work out at 70-75%, the body will quickly exhaust the glycogen stores in your muscles and will then move on to other sources. The best place for it then to find energy to fuel your movements is in the fat stores and thus you enter the ‘aerobic’ energy system. Now your body will start taking in more oxygen and your heart rate will increase. The objective is to deliver more oxygen to your fat stores where it will react and break it down (oxygen is highly reactive, which is why fire needs it to burn!).

If you start training harder though and you go above 80% of your MHR, then you will be placing even greater demands on your body. The problem with your aerobic energy system is that it’s just too slow and it’s actually too slow for this kind of exertion. Thus you will enter what is known the ‘anaerobic’ energy system, where your body will get its energy from the glucose stored in your blood.

Essentially then, medium exertion is slow enough to allow your body to burn fat while intense exertion requires you to burn carbs instead and doesn’t give you the chance to get rid of your muffin top. Thus is born the idea of the ‘fat burning zone’.

The Problem

But the thing is, even after you’ve finished training, your body still needs energy. This is necessary simply in order for us to breathe, to blink, to walk around and to think. And if you’ve been engaging in anaerobic exercise, then that means you’ll have no glucose left in your blood to fuel this activity.

So where does the body turn? You got it: to fat stores!

What this all means then, is that while regular cardio at around 70% of your MHR might lead to the best short term fat loss, training harder will actually lead to continued fat burning long after your training ends. Some people describe this as the ‘after burn effect’ and when used to its fullest, it can help you to continue burning calories throughout the day.

The Best Way to Utilize Intense Training

If you’re up to date with your training knowledge, then you might know where this leads next: to HIIT.

HIIT is High Intensity Interval Training and many people believe that this is one of the best training methods available for burning fat.

The reason is that HIIT actually involves both of these types of training, with the objective being to alternate between periods of relatively light 70% exercise and periods of much more intense training at around 90%.

What this does is causes you to change between your aerobic and anaerobic energy systems. The anaerobic then causes you to use up all of the glucose in your bloodstream, which means that your aerobic exercise becomes even more efficient at burning fat subsequently. Furthermore, you will then find that you continue to burn a lot more fat for a long time afterward and as an added bonus, HIIT is also thought to increase mitochondrial efficiency for even more fat burning in the long, long-term.

To calculate your MHR and thus ensure you’re training at the right level, try monitoring your heart rate during exercise. Push yourself as hard as you possibly can and note the highest point your heart rate reaches – this is your MHR. Now calculate 90% of that number and 70% and you can use this for HIIT.

Be careful though if you have any history of heart problems or if you’re new to training. HIIT performed properly is very intensive and can be overly challenging for complete newcomers to the gym!

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