Why do we need energy

Exercise & energy metabolism

The body is equipped with a complex system of energy supply in order to be able to provide the necessary performance in different situations. Above all, a special energy source, adenosine triphosphate (ATP), is a prerequisite for any physical activity. ATP is the universally available energy carrier in every body cell.

The cells themselves contain only small amounts of ATP, which are used up after just a few seconds. Therefore, this ATP has to be constantly restored (= resynthesized), which takes place via the energy-supplying nutrients carbohydrates and fat.

Energy metabolism with oxygen - the normal case

The energy production in the body - i.e. the ATP production - takes place primarily through the burning of fatty acids and glucose. At rest and during moderately intense exertion, the energy requirement is met primarily from the burning of fatty acids and carbohydrates, which is known as aerobic metabolism.

Activities that involve primarily aerobic metabolism include most everyday activities such as sitting, walking, standing, light housework, or office work. Longer sporting activities also mainly involve aerobic metabolism.

Depending on the intensity of the aerobic activity and the level of training, the proportion of carbohydrate and fat stores in the energy supply fluctuates.

Energy metabolism without oxygen - the exception

In the case of high exercise intensity, the body has to inject energy without oxygen (anaerobically) in addition to the aerobic metabolism. This is the case when more energy is required than can be provided by aerobic combustion of the nutrients.

The anaerobic energy supply can only bridge such situations for a very short time (about three minutes), because the muscles then tire very quickly.
Typical situations are, for example, lifting or throwing heavy objects, short, fast runs (sprints), etc.

For more information, see Energy requirements at rest and during activity.