What is behind on the fat burning myth

An overview of the energy carriers of the body

Energy supply is the supply of energy to perform muscle work (jogging, weight training, etc.). The body has different energy carriers and energy storage forms available. Adenosine triphosphate (ATP) and creatine phosphate

Our muscles have an ATP supply of approx. 6 mmol/kg. At maximum load, this stock is only sufficient for approx. 2-3 seconds. After that, the creatine phosphate helps us out for another 6-10 seconds.

More info about ATP

Glucose (blood sugar)

In a healthy and sober person, the blood typically contains a glucose portion (= blood sugar) between about 90 – 110 mg/dl. If this glucose is consumed, there is a continuous supply from the next two energy stores.


This is the “storable form” of glucose. The human skeletal musculature can contain approx. 300gr. (corresponds to approx. 1230 Kcal) and in the liver approx. 200gr. (corresponds to approx. 820 Kcal) of its store.

Depending on the intensity of the load, these glycogen reserves are sufficient for about 60 to 120 minutes to maintain the glucose supply.

More information on glycolysis and citric acid cycle

body fat

An average heavy person (with approx. 10 kg body fat) stores approx. 93,000 Kcal in the form of body fat. Body fat can be converted into acetyl-CoA and introduced into the citric acid cycle.

However, the chemical reaction of fat = energy is very slow and takes a long time. One person takes longer than another, depending on the state of training. This circumstance is probably responsible for the myth that fat burning only starts after 15 – 30 minutes.

Apples with measuring tape

facts about energy generation by fat

Fat in its storage form needs a certain time to be metabolized by the organism to such an extent that it can be introduced (in the form of acetyl-CoA) into the citric acid cycle. Simply put, energy production from fat is slow.

The conclusions are as follows:

  • The lower the continuous load, the greater the percentage of fat burning.
  • At rest, the percentage of fat burning is highest. It covers approx. 70 % of the energy requirement.
  • The percentage of energy production from fat decreases with increasing cardiovascular load.
  • At maximum cardiovascular load, the percentage of energy production from fat is lowest. It covers only 10% of the energy demand.

Relation of carbohydrates to fat burning at increasing load

But how exactly does it work? An example shows how energy production is distributed in the different stress zones.

As a test person, we have Max Mustermann at our disposal. He is 30 years old, weighs 70 kg and has a resting heart rate of 60 beats per minute.

With the carvon formula its load zones are now determined. The formulas for basal metabolic rate and power metabolic rate can now be used to determine calorie consumption at rest and during maximum stress.

Of course, hardly anyone can train at peak times for an hour. All these values serve the illustration and are rounded for didactic reasons and a better understanding half to full numbers.

The values from the diagram above are again presented in a table.

Heart rate Fat content in % KH percentage in % Calories/hour
60 70 30 80
70 65 35 150
80 60 40 220
90 55 45 290
100 50 50 360
110 45 55 430
120 40 60 500
130 35 65 570
140 30 70 640
150 25 75 710
160 20 80 780
170 15 85 850
180 10 90 920

Now Max completes 5 training sessions of one hour each in the areas of Rekom, GA1, GA2, EB and SB. The associated heart rates were determined beforehand using the carving formula.

The following values are calculated from these training units and entered in a bar chart for illustration purposes.

The values again in a table:

Recom GA1 GA2 EB SB
Heart rate 132 144 156 168 180
kcal total 580 660 740 840 920
Grease content % 35 27 23 14 10
KH component % 65 73 77 86 90
Grease content kcal 200 180 170 120 90
KH component kcal 380 480 570 720 810
Grease content gram 22 19 18 13 10
KH portion gram 93 117 140 175 197
Fat in grams for
100% fat burning
62 71 80 91 99

Is there even THE “fat burning area”

Frau joggt

  • Based on the values determined, it is clear from the diagrams and tables that the burned fat actually plays only a relatively minor role in the energy supply.
  • This is the more obvious the higher the load is.
  • The percentage of fat combustion decreases continuously with increasing load.
  • Also the actually burned calories by the fat burn decrease with rising load.
Ergo: Postulating a special “fat burning area” is simply an IRREFLEENDING HALFWAY !!!

It is interesting to look at the last row in Table 2. There the equivalent of the total calories burned is displayed in grams of fat.

What consequences does this have for my endurance sport?

None! Important for losing weight is not only the proportion of fat burning during sport but the “negative energy balance” throughout the day.

The more calories you consume per day than you consume, the more fat your body breaks down, regardless of the amount of fat burned during exercise.

Fat burning in ambitious sports

The ability to burn fat plays an increasingly important role here the longer the load lasts. The reason is that the body’s own glycogen stores contain approx. 2000 Kcal. The provision of energy by carbohydrates is therefore also limited in time. The higher the load, the faster this storage is empty. The higher the percentage of fat burning, the longer the carbohydrate storage lasts.

An athlete who can burn more fat at the same endurance level has a clear advantage over his opponent. In addition, there are various scientific studies with the same name on this subject.

This post is also available in: German

William C. Hilberg
As an author, Mr. Hilberg has published several papers on health issues that have gained international recognition. He is close to nature and loves the seclusion and activity as a freelance journalist. In his function as editor William C. Hilberg manages the entire content of PENP. Our team greatly appreciates his expertise and is proud to have him on board.