Energy supply in the muscle

Our organism has several possibilities for providing energy in the muscle. The boundaries are fluid and there are always intersections.

That is why the topic is very complex, but important for our understanding of the function of endurance and a successful endurance training.

  • The energy supply in the muscle is usually done aerobically.
  • This happens via the citrate cycle in the mitochondria of the muscle cell.
  • The proportion of fat in the resting state is the highest (up to 70%).
  • Only in an emergency or in the initial phase of muscle contractions is the energy supply anaerobic (up to approx. 60 sec.).
  • After that (over 60 sec.) the nutritive reflex takes over the energy supply of the musculature.
  • All these forms of energy supply are briefly presented and explained in this article.
  • You will find a detailed explanation of the individual types of energy supply under the article The cell – structure and function.

The energy supply in the muscle in 4 phases


Phase 1: creatine phosphate

From 3 to 10 seconds

Creatine phosphate decomposes into creatine and phosphate when required. No oxygen is required (anaerobic). In addition, no lactate (alactacid) is produced. The energy released is used directly to build ATP from ADP and phosphate. Sufficient for approx. 3-10 seconds load.

Period: 3 to 10 seconds

Energy supplier: Creatine phosphate

Provision method: anaerobic-alactacid

Phase 2: Adenosine triphosphate

Up to 3 seconds

ATP is an energy store in our musculature, which disintegrates into ADP and phosphate when needed and releases energy in the process. Our muscles have an ATP supply of approx. 6 mmol/kg. At maximum load, this supply is only sufficient for approx. 2-3 seconds.

Period: Until 3 seconds

Energy supplier: ATP

Provision method: anaerobic-alactacid

Phase 3: Glycolysis

From 10 to 60 seconds

Glycolysis takes place permanently in the cytoplasm of the (muscle) cells. At rest or under low stress, practically all the energy generated by glycolysis is used. At an approximate maximum load (95%) or at the beginning of a continuous load, the energy is sufficient for approx. 60 seconds.

If the power demand is too long or too high, there is a sudden increase in lactate and the power output must be interrupted or greatly reduced.

Period: 10 to 60 seconds

Energy supplier: Carbohydrates (glucose)

Delivery method: anaerobic lactacid

Nutritive Reflex

After approx. 60 seconds of exercise, the nutritive reflex takes effect and ensures that the muscle is sufficiently supplied with nutrients (oxygen, glucose, etc.). Part of our vegetative nervous system (here sympathetic nervous system) is used to adapt our cardiovascular system:

  • The heart rate and beat volume of the heart increase (= cardiac output increases).
  • The vessels of the musculature expand (= dilatation).
  • The breathing rate increases to have more oxygen available.

Phase 4: Citrate cycle

Metabolism in which oxygen is required and lactic acid (= lactate) is formed. The organism uses 2 different energy sources: carbohydrates and fat. The energy production takes place in the mitochondria (= power stations of the cells) and is sufficient for several hours depending on the load.

Period: Over 60 seconds

Energy supplier: Carbohydrates, fat

Delivery method: aerobic lactacid

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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.