Secrets of the Fat Burning Zone

Authored By Ben Fisher

So, you want to lose some excess fat? You’re at the gym, an you think, “I’ll do a cardio workout – I must be able to burn fat that way.” You alight your chosen machine and look at the large array of buttons and instructions displayed. Your eyes settle on a coloured chart showing you the intensities for the “Fat Burning Zone.” “That’s just what I’m looking for,” you think, and you start your workout believing that the fat is just going to melt away…Unfortunately, it’s not entirely true!

A fact not usually known by most gym-goers is that you are constantly burning body fat; when you are sitting down, when you are walking, running and even sleeping. The body requires predominantly fat and carbohydrates for energy but at lower levels of exercise intensity that ratio is skewed towards fat – “Excellent!”, I hear you say. As a guide one gram of fat will provide 9 kcals of energy and carbohydrates will provide 4 kcals of energy.

What many people do not realise is that as your exercise intensity levels increase the ratio at which your body uses fat and carbohydrate (in the form of glycogen) changes. At lower intensities (Up to 60% of your Maximum Heart Rate*) for the total calories you use up, you are burning almost 50% from fat stores. This is the Fat Burning Zone that the cardio machines highlight. As your exercise intensity increases to 75% of your max HR the ratio changes and you will only burn around 35% of the energy from fat and the remainder from glycogen (stored sugar) but the total calories utilised for the same period of exercise will increase significantly (depending on your weight and sex this can more than double). If you increased the intensity up to 90% of your max HR, again the ratio of fat burned will reduce to around 17% but the total calories burned will be significantly higher. This is because the body uses the creatine phosphate energy system at very high levels of intensity as opposed to fat or glycogen.

In summary, it is not the case that the Fat Burning Zone will burn the most fat, it is just indicating the body’s source of the energy. This means that you need to work harder in your work out than the machines suggest in order to get the best results. It may not be what you want to hear but why waste any more time with misguided work outs?

If your overall goal is to lower your body fat or lose weight, it’s simply a basic equation:

Weight loss = Energy Out > Energy In And Higher Intensity = More Calories Expended

The intensity you choose to work out should be based on your current fitness level and also your exercise objectives. Don’t forget that you can vary your workouts with interval training or resistance training which both have an excellent EPOC effects (Excess Post-exercise Oxygen Consumption). This means that you continue to have a raised metabolism for several hours after you have stopped exercising, expending even more calories. Now that should be more what you want to hear!!

*Maximum Heart Rate is calculated as approx 220 – age

Statistics courtesy of Premier International and based on 30 minutes exercise on a treadmill.


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