Anaerobic Glycolysis Energy system

As the body exercises there is an increased demand for energy. The anaerobic glycolysis energy system produces energy by the breakdown of glucose in the absence of oxygen, to produce energy at a fast rate. However this pathway cannot be sustained as it produces fatigue inducing by-products.


(Image from Jacaranda textbook, live it up 2)

Anaerobic Glycolysis: Process of ATP production

This process involves glycogen being converted into glucose and then into pyruvic acid, this takes place within the cytoplasm of a cell not in the mitochondria. When glucose is broken down into pyruvate, energy is produced for the synthesis of ATP, 2 ATP are produced per glucose molecule broken down. However  pyruvic acid with insufficient oxygen is converted into lactic acid which dissociates into lactate and hydrogen ions. It is the hydrogen ions that cause the experience of fatigue as they raise the acidity within the muscle interfering with muscle contraction, with oxygen these are removed. After exercise is finished or intensity reduced there will be sufficient oxygen to convert lactate back into glycogen so it can be used as a fuel.

Key Aspects of the Anaerobic glycolysis energy system

Fuel Source

Carbohydrates are the main fuel source for this energy system, carbohydrates are broken-down into glucose and stored as glycogen in the muscles and liver.


Glucose is stored mainly in the muscles and in small amounts within the liver in the form of glycogen.

Intensity of activity

High intensity around 85-85% max heart rate.


The anaerobic glycolysis system is dominant for around 5-60 seconds for maximal activity.

Peak effectiveness (power)

The anaerobic glycolysis system is most effective at the time period of 10-15 seconds this means it is providing energy at its greatest rate before metabolic by-products begin to accumulate causing a decline in effectiveness.

Rate (Speed of ATP production)

This  energy system provides energy at a fast rate as there are only 12 chemical reactions making it much faster than the aerobic energy system.

Yield (Amount of ATP produced)

The yield is more than the ATP-CP energy system but still significantly less than the aerobic system. It produces around 2 ATP per molecule of glucose broken down.

By-Products of this system

Is lactic acid, this dissociates into H+ ions and lactate. H+ ions raise muscle acidity interfering with muscular contractions and the function of enzymes causing fatigue.

Advantages of the Anaerobic Glycolysis system

  • Fast synthesis of ATP.
  • Useful for high intensity activities when the body cannot get enough oxygen in to carry out aerobic glycolysis for the majority of ATP synthesis.
  • Produces more ATP then the ATP-CP energy system.

Disadvantages of the Anaerobic Glycolysis system

  • Produces large amounts of H+ ions that cause fatigue.
  • Produces relatively small amounts of ATP when compared to the aerobic energy system.

ATP as an energy storage molecule

Adenosine triphosphate(ATP) consists of one adenosine molecule with three phosphates connected to it as seen in the image below. Energy is stored within the bonds of the phosphate molecules, when these bonds are broken (usually the bond between the two end phosphate molecules) the energy can be used for muscle contraction or other processes that require energy. The body uses ATP as a temporary storage molecule as the end product to provide energy, hence all the energy systems in the body provide energy for the synthesis of ATP which is ultimately used to provide energy for muscle contraction. When the bond between the last two phosphate molecules is broken adenosine diphosphate(ADP) and an inorganic phosphate(Pi) are formed, an organic phosphate will then need to be reattached to synthesise ATP and this process requires energy.1

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  1. Jacaranda textbook, live it up 2