The Fat Burn Zone – fact or fiction?

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Those who undertake exercise regimes will no doubt have heard of the Fat Burn Zone which has been discussed in great detail over the years. Some experts swear blind that it exists while others suggest it is a myth which has somehow become “reality” in the minds of many people. So, the Fat Burn Zone, is it fact or is it fiction?

What is the Fat Burn Zone?

The general understanding is that by working out between 55% and 65% of your full workout capabilities you will burn more fat. This is commonly referred to as the “Fat Burn Zone” and while there is some truth in the concept, it is not quite as straightforward as many would have you believe.

Body fuel during exercise

Before we look at the Fat Burn Zone in more detail let’s take a look at the types of fuel your body requires during exercise. We know that it comes from two places, fat or glycogen stores (carbohydrates stored in your muscles and liver) and when and how much is taken from each resource will depend upon the level of exercise.

To give you an idea, the split between fat and glycogen is around 60% to 40% when exercising at 50% of your maximum heart rate. When this is increased to 75% the ratio falls to 35% to 65% and continues to reduce the harder you push your heart. So, you will be forgiven for assuming that the “Fat Burn Zone” does exist and can be useful. However, that is not the full story!

Calorie intake

There have been many research programmes over the years which highlight the fact that for example a 30 minute exercise routine for low intensity groups will burn around 200 calories. A 30 minute routine for high-intensity groups will burn around 400 calories. So, while we appreciate that burning fat held within the body is important it is also important to burn excess calories. This is where the balance between calorie intake and calorie burn off comes into play – the more calories you consume the greater the fat storage within your body. There is definitely something in the old adage that to lose weight you need to reduce your calorie intake and increase your calorie burn but in a safe manner.

The afterburn effect

While many people like to discuss the Fat Burn Zone there is little or no discussion about the afterburn effect. This is the impact which exercise has on your body for a short period after you stop exercising. When it comes to fat burning, there is no afterburn effect for low intensity exercises, when you stop your body simply stops burning fuel – in this instance the majority of which is fat. However, for high-intensity exercise regimes the situation is very different.

A study by Dr Christopher Scott of the University of Southern Maine has been covered in great detail across the Internet. He undertook an experiment with people carrying out low intensity exercises versus those carrying out high-intensity exercises. This perfectly illustrates the difference between the two:

The low intensity group cycled at a steady rate for 3.5 minutes
The high-intensity group carried out three 15 second sprints going at the maximum pace possible.

The results of this research are amazing because during the period of exercise the low intensity group burned 29 calories and the high-intensity group burned just 4 calories. However, due to the afterburn effect (after they finished exercising) the low intensity group had burned a total 39 calories while the high-intensity group had burned a total of 65 calories. This shows the benefits of afterburn and the fact that it is more prevalent in high-intensity exercise regimes than their low intensity counterparts. The high intensity group burned more than 10 times the number of calories after exercise than during the exercise period!

Conclusion

There is a Fat Burn Zone, seen between 55% and 65% of your maximum heart rate, where the body will burn more fat than glycogen. However, as we have highlighted above this does not give the overall picture and the impact of afterburn. The idea that it is somehow “better” to depend on low intensity exercise regimes as opposed to your calorie intake, and high-intensity exercise regimes, is flawed. Yes, looking at the Fat Burn Zone in isolation seems to support this idea but looking at the overall picture there are a lot more issues to consider.

If your reason for exercising is purely to reduce your body fat then there are many forms of exercise which will help. However, ultimately it is the balance between your calorie intake and the number of calories you burn. How you balance this is up to each individual.