Metabolism basics

Aerobic and anaerobic metabolism

Two ways of generating energy

Surely you’ve heard of the terms “aerobic” and “anaerobic” metabolism. We explain in our post what are the differences between the two metabolic processes and why your body needs oxygen to burn fat.

Our metabolism is a true marvel (see The Metabolism – What Is That?).

The power plants in our body cells, the mitochondria, are constantly busy providing energy to our bodies. Especially the muscle cells require a lot of energy, e.g. at sports loads.

ATP: The energy currency of the organism

What kind of car is gasoline is ATP (adenosine triphosphate) for the human body – it is, so to speak, the universal energy “currency”. The cleavage of an ATP molecule to ADP releases energy. The body has to recreate it again and again, so to speak “to recycle”. This can be done in two ways:

in the aerobic metabolism: with oxygen supply
in the anerobic metabolism: without oxygen supply
The terms are derived from the ancient Greek word “ἀήρ” (= aer), which means “air”. As a rule, the body gains its energy through the aerobic metabolism.

In this process, the so-called cellular respiration is completely gone: energy, say ATP, is obtained with oxygen supply.

The end products of this metabolic process are carbon dioxide and water released, which is largely exhaled through the lungs.

The anaerobic energy metabolism

The anerobic energy metabolism begins when the body is exposed to short but very intense physical stress.

Pulse and respiratory rates are rising, but by no means enough to provide enough energy to the entire organism.

Take a 400 meter runner as an example. Already after the first 6-8 seconds of its run all ATP, that is, energy reserves in the muscles are used up.

With this very heavy physical load, the runner’s lungs fail to provide the body with enough oxygen to produce energy. What to do? The body is intelligent and switches to the fast anaerobic metabolism.

This means that the body converts glucose into so-called lactic acid fermentation in lactate and 2 mol ATP. For this type of energy production – as with all fermentation processes – no oxygen is needed. The advantage is that the body quickly recovers energy, ie ATP.

Carbohydrates are the most important source of energy

The energy needed to extract ATP can be gained by burning the body’s carbohydrates, proteins and fats – which we ingest daily through our diet. Which of the three so-called macronutrients metabolism uses as an energy source depends on the following factors:

  • the nutritional and training state and
  • whether there is just enough oxygen available or not – accordingly, the metabolism runs off aerobically or anaerobically.

Most important, however, are the carbohydrates, or rather, the glucose (glucose). First, because the body can burn glucose with or without oxygenation (aerobic or anerobic), second, because important organs such as the brain and red blood cells can only gain their energy from glucose.

Lactate formation: The power limiting factor

After 2 minutes we come but literally “out of breath”. The muscles over acidify due to the lactate (lactic acid) and can not work any longer.

This means that the runner has to give up maximum load after about 2 minutes or drastically reduce his running speed. So no runner is e.g. able to complete a marathon in sprint speed.

The Aerobic Energy Metabolism

In practice, this means that workloads or workouts that go beyond two minutes must be planned from the outset so that the body can only cope with it with constant oxygen supply.

That is, the energy supply must be aerobic. For long loads, v.a. which last longer than 30-60 minutes, the body also switches on the burning of fat as an additional source of energy or increasingly gains its energy from fats.

As mentioned above, the ATP is thus obtained in the aerobic energy metabolism via the fully expiring cell respiration. That is, if we can continuously inhale as much oxygen as the body needs during a physical activity, we are in the aerobic area.


The body has two metabolic pathways for energy: the aerobic (with oxygen supply) and the anerobic (without oxygen supply) metabolism. The most efficient way is the aerobic way, because only here the cellular respiration is completely exhausted.


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