Most of us trying to lose weight will be familiar with the ‘fat burning zone’. It is regarded as the optimal range our heart rate should be to burn fat.
We are told that exercising at an intensity between 60-70% of our maximum heart rate (220 minus your age) will burn the most calories from fat. This type of intensity would typically represent a brisk walk.
The theory behind this is very simple.
The lower the intensity of the exercise, the greater percentage of calories burnt will come from our fat stores.
Inversely, working in the ‘cardio zone’ between 70-85% of our maximum heart rate, will mean the main energy supply used comes from our stored carbohydrates.
You may have seen these training zones on popular pieces of cardio equipment and I know many gym members still keep their heart rates firmly in the ‘fat burn zone’ in a determined attempt to lose weight and ensure they are burning fat rather than sugar.
I have spoken to many people who get worried if their heart rates creep too high into the dreaded ‘cardio zone’ as they fear they will not be utilising the right source of energy.
The science behind all of this is that when we train at a higher intensity it is difficult to obtain, transport and use sufficient oxygen to metabolise fat leading to carbohydrates as the preferred source.
But there is a massive flaw to this theory.
If we did truly burn fat at a lower activity intensity then surely we would be burning fat when we are asleep or watching television as 90% of calories consumed when we are inactive comes from fat?
Obesity would be obsolete.
In fact, we wouldn’t need to exercise at all and I would be out of a job!
But the main flaw in the argument is the disregard for total calories burned.
Let’s take this example of a 147-pound woman exercising at two different intensities. Walking in the ‘fat burn zone’ would use 40% of calories from fat as opposed to 25% if she was running in the ‘cardio zone’ but walking would only burn a total of 130 calories compared to 430 calories when running.
It is the total amount of calories burned and not the type of calories that matter when it comes down to weight loss.
Another important factor is the concept of Excess Post-exercise Oxygen Consumption or E.P.O.C for short.
Commonly referred to as the ‘after-burn effect’ it is the amount of time after exercise has finished when the metabolism stays elevated above normal resting levels and therefore burning more calories.
This happens due to all the physiological processes that occur during exercise which are energy consuming and fueled by our fat stores.
E.P.O.C is longer with greater training intensity.
Research shows we need to exercise at about 70% of our maximum heart rate (MHR) for any significant after-burn effect. Vigorous exercises at 80% of our MHR can produce over 10 hours of fat burning!
Remember, when you workout at a lower intensity your metabolism will return to normal as soon as your heart rate drops.
Here are my recommendations for ultimate fat burning:
- Only choose low intensity or the ‘Fat Burn’ zone if you are unfit or deconditioned.
- Total energy expended is the most important figure not the percentage of fat compared to carbohydrate you might be burning.
- Fitness should be the primary goal not fat burning. The fitter you are, the easier it becomes to burn fat.
- The type of cardio you use is not important. Just get your heart pumping whether it is running on the treadmill, climbing stairs, skipping or sprinting up sand dunes.
- Try to workout to at least 70% MHR to increase calorie expenditure and promote fat loss.
- Resistance and bodyweight training will dramatically boost your resting metabolic rate and significantly contribute to burning more calories.
- Interval training has been proven to be most effective in fat burning. An example protocol is 3-4 sets of running at 80-90% MHR for 30-60 seconds with 3-5 minutes rest in between each set. This shouldn’t take longer than 10 minutes.
Trying to burn fat by working out at a lower intensity simply does not work.
Exercise is much like life. You only get out what you put in.