Glycolysis (Glycolytic System)

Glycolysis refers to the anaerobic breakdown of glucose or glycogen for energy. There is a delay of 5 to 10 seconds after the initiation of activity before the glycolytic system can supply energy to working tissues. The six-carbon glucose molecule is phosphorylated and broken into two three-carbon molecules (glyceraldehydes-3-phosphate, or G3P). Each molecule of G3P is converted into pyruvate with the formation of ATP. The glycolytic reaction creates two molecules of ATP for each molecule of glucose; it creates three molecules of ATP for each molecule of glucose if glycogen is the initial substrate. The pyruvate may be converted to acetyl-CoA for later storage as fat or conversion to lactate. In either case, the fat or lactate created from pyruvate can be oxidative sources of energy. Glycolysis has half the power to create energy as the PCr system but has three times the capacity. The combination of PCr and glycolysis can support predominantly anaerobic maximal work for approximately 90 seconds, often referred to as the anaerobic maximum.