Aerobic and anaerobic are two terms that occur more frequently in endurance sports than you might think. Aerobic refers to metabolic processes in the organism that take place with the participation of oxygen, while anaerobic refers to metabolic processes that take place without the participation of oxygen.

The difference between these two types of metabolism is crucial for endurance athletes, as aerobic energy production enables them to perform at their best over a longer period of time.

Aerobic

From a chemical point of view, aerobic processes are oxidations. If the oxygen supply is interrupted or if a system based on oxidation is overloaded, anaerobic biochemical reactions, in particular fermentation processes, can predominate or gain the upper hand completely.

One example of this is the metabolism of muscles, even in humans. At low intensity, energy production is predominantly aerobic through the oxidation of fatty acids and the aerobic metabolism of pyruvate or lactate formed from glucose through glycolysis.

If the muscle is subjected to greater strain, the proportion of energy obtained through glycolysis increases (see aerobic threshold). However, the lactate produced in increasing quantities can still be metabolized - in small quantities in the glycolytic muscle fibres, under good training conditions mainly in the ST fibres and in the heart muscle - so that the lactate level in the blood does not rise excessively. Only when this oxygen-dependent system is overloaded (which is not due to a lack of oxygen) does a sudden rise in lactate occur (until the individual anaerobic threshold is reached).

Examples of aerobic processes:

• Breathing
• Composting
• Nitrification

Anaerobic

Anaerobic, also known as anaerobes, refers to life without oxygen (deoxygen O2). Living organisms that do not require molecular oxygen for their metabolism are called anaerobes. Those anaerobes that are inhibited or even killed by O2 are more precisely referred to as obligate anaerobes.

Anaerobic respiration is a process in which organisms produce energy without using oxygen. In contrast to aerobic respiration, where oxygen is used as the final electron acceptor, anaerobic respiration uses other electron acceptors as oxidizing agents instead of O2 for oxidative energy metabolism. Commonly used alternative electron acceptors are: Nitrate, trivalent iron ions (Fe3+), tetravalent manganese ions (Mn4+), sulfate, sulfur, fumarate and carbon dioxide (CO2). These redox reactions are known as anaerobic respiration.

Anaerobic protozoa are the oldest life forms on Earth, preceding the first photosynthetically active protozoa from the Precambrian, which excreted O2. With its accumulation in the hydrosphere and the atmosphere, living conditions changed on a large scale (see Great Oxygen Catastrophe). Even the anaerobic organisms living today do not require oxygen for their metabolism and can be roughly differentiated according to how well they cope with an oxygen-rich environment:

Obligate anaerobes are organisms that metabolize exclusively anaerobically and require a habitat with anoxic conditions. In microbiology, a distinction is made between moderate forms, which cannot grow in the presence of oxygen, and strict forms, which are damaged or killed by O2.

Aerotolerant anaerobes are organisms that metabolize exclusively anaerobically, i.e. do not consume O2, but tolerate the presence of oxygen and can therefore live under oxic conditions.

Facultative anaerobes are organisms that can metabolize anaerobically under oxygen-free conditions, but can use O2 for metabolism in the presence of oxygen.