The Myth of the Fat Burning Zone 

Why exercising in the "fat burning zone" could be making you FATTER!  

-By Mark Woodgate


This information may completely change your outlook toward fitness and

Some myths never die. And the idea of the "fat burning zone" is arguably one of the most misunderstood fallacies in the fitness industry today. 

Let's begin by defining the theory of the fat burning zone. The theory is that by maintaining your heart rate in the zone of 50% to 65% of your maximum heart rate (low intensity cardio), your body will burn a highter percentage of fat as a source of energy during the exercise period. While this is actually TRUE, read on to find out why exercising in the fat burning zone may actually be making you FATTER

The following fat burning information is VERY important

During a cardiovascular workout your body uses two primary sources of energy: 

1) Adipose tissue (body fat)  

2) Carbohydrates

Low intensity cardio (LIT) or exercising within the fat burning zone, results in an increased increased utilisation of fat compared to carbohydrate. 

High intensity cardio (HIT) produces a greater utilisation of carbohydrate compared to fat. 

HOWEVER, lets assume that you exercise for 15 minutes using both LIT and HIT.

Your total energy expenditure is much greater with HIT cardio simply because you're exerting more effort. Relatively speaking, HIT will use a lower percentage of fat versus carbohydrates, however, in ABSOLUTE terms your net fat utilisation during exercise is actually higher.   

Thanks to a study by LaForge and Kosich (1995) this was demonstrated with a 60 minute cardiovascular training session using low and high intensities. 

These are the results:

LaForge and Kosich (1995)

Lower intensity

Higher Intensity

Cardio Duration

60 mins

60 mins

VO2max (A measure of intensity)



Total calories burned















As you can see, exercising at a higher intensity for a given time proved to burn more fat than exercising at a lower intensity. But don't be fooled by the percentages - it's the TOTAL FAT burned that is important. 

However the real advantage of high intensity training is the post workout 'afterburn.' Simply put, when you exercise at a higher level of intensity you continue to burn calories AFTER the workout has finished.  

This residual calorie burn can last up to 48 hours. In exercise science this is called E.P.O.C - an acronym which stands for 'Excess Post exercise Oxygen Consumption.

In other words, your metabolism is elevated for a much longer period using higher intensity than with traditional cardio or working out in the "fat burning zone."

Why LESS Cardio is 9 Times MORE Effective for Fat Burning 

If we were to compare 60 minutes of LIT to just 15 minutes of HIT and took a snapshot over a 24 hour period, it would look something like this:


Low intensity

High Intensity

Cardio Duration

60 mins

15 mins

Fat burned during cardio



Fat burned after cardio


A lot

Total fat expenditure over 24 hours


A lot

Something extraordinary happens when you exercise at a higher level of intensity. 

A study at Laval University in Quebec published in a journal called 'Metabolism' back in 1994, demonstrated that high intensity exercise burns significantly more body fat than steady state endurance exercise. 

In this case we're not talking about calories burned during exercise, or whether they came from fat or carbohydrate, we're talking about actual fat that disappeared from actual bodies. 

This research concluded that for every calorie you burn during high intensity exercise, your body strips off 9 times more body fat than a calorie burned during low intensity cardio. (see study here)

"Every calorie you burn during high intensity exercise strips off 9 times more bodyfat than a calorie burned during low intensity cardio"

Therefore, if your goal is to lose body fat in the most time efficient way possible, high intensity short duration workouts provide amazing results compared to low intensity, long duration workouts.

You Can Either Work Out for a Long Time OR Work Out Intensely, But You Can't Do BOTH!

Intensity is a function of the duration of your workout. In other words, as your body progressively fatigues, the lower the intensity of the workout.   

But here's the real problem with long duration, low intensity workouts...

Exercising for long periods produces higher concentrations of a hormone called cortisol. Cortisol is a muscle wasting hormone and with loss of lean muscle comes a lowered basal metabolic rate. This is why over time, long duration low intensity cardio can actually make you FATTER (especially if this is the only type of exercise you do and there is no strength training element to preserve muscle tissue.) 

Boost your youth hormone by 771% !

High intensity interval training engages your super fast twitch muscle fibres which in turn triggers the release of growth hormone. Human growth hormone (HGH) is assocated with longevity, increased bone density, accelerated fat loss and maintenance of lean muscle - all of which become especially important as we age.

Phil Campbell, a veteran in the field of fitness with over 35 years experience training professional athletes, conducted an 8 week study of high intensity interval training. The results were truly phenomenal and resulted in an average HGH increase of 771%! Moreover, this translated to an average 31% body fat loss amongst participants.

(nb: It should be noted that only high intensity interval training and strength training workouts trigger the release of growth hormone, whereas low intensity cardio does not.) 
For more info re: Phil Campbells 8 week study, click here

What about Fitness? High or low intensity training?

When I began my personal training career in the mid 90's I came across some studies by Japanese exercise scientist, Izumi Tabata. Dr Tabata and his team compared low intensity exercise (L.I.T.) to high intensity interval training (H.I.I.T.)

In Tabata's study, one group performed a full 60 minutes of moderate intensity cardio exercise 5 days per week. Group two also performed cardio exercise 5 days per week however this group performed just 8 x 20 second sprints of high intensity cycling with a 10 recovery period in between. This was preceded by a warm up and followed by a warm down. 

Total exercise time? 4 minutes!

The results were extraordinary to say the least. Tabata discovered that the athletes using the high intensity interval programme increased their fitness levels much faster than athletes on a typical endurance training regime, this despite the VAST difference in the amount of time each group spent working out. 

The 6 week results of the Tabata studies are as follows:

Tabata Studies (1996)

70% VO2max

170% VO2max

Cardio Duration

60 minutes

4 minutes

Aerobic fitness increase (VO2 max)



Anaerobic Capacity INCREASE



Of particular interest was the fact that participants who performed the 4 minute workouts not only increased their anaerobic capacity (the type of exercise that requires maximum, sprint like effort) but also their aerobic capacity. (The term "aerobic" refers to maintaining a steady pace with the idea of developing endurance) 

In contrast, group 1 showed NO anaerobic fitness increase with a 10% increase in aerobic fitness, whereas group 2 showed a 28% and 14% increase respectively - all with only 4 minute workouts, 5 times per week! 

It should be noted that the participants in question were highly trained athletes and the level of exertion required would not be suitable for an untrained individual. Fortunately we can still apply the fundamental tenets of this protocol and use levels of exertion that are relative to each individual - whether beginner, intermediate or advanced. 

These interval workouts are the basis for Body Blueprint's workout programmes and have enabled our clients to dramatically lose body fat and increase their fitness levels in very short periods of time. 

How can I add High Intensity Interval Training to my workouts? 

Choose a cardio machine that allows you to quickly accelerate and decelerate. Ideally this machine will target the whole body (burns more calories) such as the elliptical trainer or rowing machine. Alternatively this can be performed as walk or jog / sprint outside. (A treadmill is not suitable as the short intervals do not provide adequte time to move from slow to fast speeds - and vice versa)  

Next, choose 2 speeds that are based on YOUR level of fitness. The first represents 50% of your perceived maximum speed. The second represents 90% of your perceived maximum speed. (Remember, these speeds are unique to you and are based on your level of fitness)

Start with a 2 minute warm up at your perceived 50% speed. For minutes 2-4 you will perform intervals of 20 seconds fast (your perceived 90%) and 10 seconds slow (your perceived 50%) This 4 minute cycle will be repeated 3 - 5 times. (12-20 minutes in total )  

Here is an example of H.I.I.T. (also known as Guerilla cardio) using the elliptical trainer:                                 


Perceived Intensity


0.0 – 2.00



2.0 – 2.20



2.20 – 2.30



2.30 – 2.50



2.50 – 3.00



3.00 – 3.20



3.20 – 3.30



3.30 – 3.50



3.50 – 4.00



(Repeat 4 min cycle 3-5 times)



Is there still a place for traditional low intensity cardio workouts? 

Yes. Especially if you're new to exercise or your chosen sport requires long distance training. However, with that in mind (and based on the studies above) I encourage you to add high intensity interval training to your programme as soon as possible - especially if your goal is to lose body fat as efficiently as possible, increase your aerobic and anaerobic fitness, and not to mention, save many hours of unproductive cardio time! 

Say goodbye to the "fat burning zone" and welcome to the NEW ERA of High Intensity Interval Training for MAXIMUM Fitness and Fatloss! 

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