Energievoorziening voor spiercontractie

The fibers in an actively contracting muscle require an enormous amount of ATP for continuous contraction cycles.

This ATP demand can be met via three routes: direct phosphorylation of ADP, aerobic respiration, and anaerobic glycolysis.

With the onset of contractions, available ATP depletes within a few seconds, and the muscles turn to phosphocreatine reserves for energy.

Phosphocreatine is a unique small molecule with a high-energy phosphate bond.

The enzyme creatine kinase catalyzes the transfer of phosphate from phosphocreatine to ADP, forming ATP and creatine. 

After exhausting phosphocreatine, muscles start utilizing blood glucose and muscle glycogen stores.

The muscle fibers break each glucose molecule into two pyruvate molecules coupled with ATP formation using glycolytic enzymes in the cytosol.

When there is sufficient oxygen, the pyruvate undergoes aerobic respiration in the mitochondria and is broken down into carbon dioxide and water, producing a large amount of ATP.

But if oxygen is insufficient and the ATP requirement is pressing, anaerobic glycolysis is used as the quick source of ATP combined with converting pyruvate into lactic acid.