Achievement Standard 2.3

Energy systems

ENERGY SYSTEMS Energy for muscular activity and other biological work comes from the breakdown of adenosine triphosphate (ATP). ATP loses one phosphate molecule and breaks down to Adenosine diphosphate. As a result of this breakdown energy is released which is used at cellular level to allow muscle contraction. Since the store of ATP in the body is limited, we must regenerate its ATP as quickly as it is broken down. This regeneration connects the ADP and Pi together again to create ATP once more. This regenerating of ATP is done by the breakdown of fuel reserves.There are three energy systems for this:

1. Creatine Phosphate System (ATP-PC system)2. Anaerobic system (Lactic Acid system)3. Aerobic system

The Creatine Phosphate SystemThe Creatine phosphate system (ATP- PC system) uses a chemical fuel reserve, Creatine Phosphate (CP), which is stored in the muscle. This process is anaerobic meaning it does not require the use of oxygen for it to work. CP is broken down into Creatine and Phosphate and the energy released from the breakdown is used to combine ADP and Pi to produce ATP. The supply of CP is limited and can only be used effectively for 10 to 20 seconds. When sufficient oxygen is available the body regenerates CP ready to use again if needed.

The Anaerobic SystemThe lactic acid system uses the anaerobic breakdown of glycogen and occurs in the cytoplasm of the cell. Glycogen is the form that carbohydrate is stored in the body (in the liver and in muscles). This process does not require oxygen and generates a net return of 3 molecules of ATP regenerated for each molecule of glycogen broken down. The end result of this breakdown is pyruvic acid. At this stage the pyruvic can follow two courses of action. In the first if insufficient oxygen is available for further breakdown the pyruvic acid becomes lactic acid and is stored until sufficient oxygen is present and it then becomes pyruvic acid again and begins its aerobic breakdown.

The Aerobic System

The Aerobic system produces its energy by utilising oxygen. It is performed in the mitochondria of the cells through a series of chemical reactions known as the Krebs Cycle. Here we have the continued breakdown of glycogen from when it becomes pyruvic acid and enters the mitochondria. Fats (and in extreme circumstances proteins) are also broken down here as they can only be broken down aerobically. The results are the regeneration of ATP molecules and the production of by-products - water and carbon dioxide. The aerobic breakdown of glycogen generates a further 39 molecules of ATP.

Summary of Energy SystemsATP-CP System Lactic Acid System Aerobic System

Anaerobic Anaerobic AerobicVery rapid Rapid SlowChemical: CP Food: glycogen Food: CHO, Fat,

ProteinVery limited ATP Limited ATP Unlimited ATPMuscular stores Lactic Acid causes No fatiguing limited fatigue by-productsExplosive, sprint 1 to 3 min duration Endurance100m 400m Marathon