Energy systems

Energy systems

There are three sources of Adenosine triphosphate (ATP), the body's main energy source on the cellular level.

ATP-PC System (Phosphogen System) - This system is used only for very short durations of up to 10 seconds. The ATP-PC system neither uses oxygen nor produces lactic acid and is thus said to be alactic anaerobic. This is the primary system behind very short, powerful movements like a golf swing or a 100m sprint. []

Anaerobic System (Lactic Acid System) - Predominates in supplying energy for exercises lasting less than 2 min. Also known as the Gylcolytic System. An example of an activity of the intensity and duration that this system works under would be a 400m sprint. []

Aerobic System - This is the long duration energy system. By 5 min of exercise the O2 system is clearly the dominant system. In a 1km run, this system is already providing approximately half the energy; in a marathon run it provides 98% or more. []

ATP-PC System

The creatine phosphate or ATP-PC system is unrivalled in our bodies for instant production of energy; it works by reforming ATP by breaking down a chemical compound called creatine phosphate which creates provides sufficient energy for some ADP to reform into ATP.
This is the first energy pathway that is used by our bodies to resynthesise ATP (Adenosine Tri Phosphate) without the use of oxygen. As it does not use oxygen it is therefore an anaerobic energy system, although this system does not produce lactic acid (lactate 2C3H6O3). Instead of oxygen it uses another chemical known as CreatinePhosphate found in the muscle cells. THIS IS NOT USED FOR MUSCLE CONTRACTION but is mainly used for resynthesising ATP and to maintain a constant supply of energy. These Reactions Occur very rapidly and only last up to ten seconds, which means it is used in activities of high intensity. (this only lasts for a short peroid of time)

Anaerobic System

The lactic acid or anaerobic glycolysis system converts glycogen to glucose. Then, with enzymes, glucose is broken down anaerobically to produce lactic acid; this process creates enough energy to reform ATP molecules, but due to the detrimental effects of lactic acid build up, this system cannot be relied on for extended periods.

Aerobic System

Aerobic -In the presence of, requiring, or utilizing oxygen. The purpose of this system of producing energy is to produce 38 molecules of ATP from each molecule of Glucose that is used. ATP is broken down in the body to give ADP and an inorganic phosphate plus energy. This energy system is used throughout the body, for producing energy for all metabolic processes, in exercise it is used for sub-maximal exercise such as long distance running. This system is used to regenerate the ATP that is used for energy in the body.

This energy system is otherwise known as 'aerobic respiration' and can be split into 3 separate stages: Glycolysis, The Krebs Cycle and Oxydative Phosphorylation.

Glycolysis - The first stage is known as glycolysis, which produces 2 ATP molecules, a reduced molecule of NAD (NADH), and 2 pyruvate molecules which move on to the next stage - the krebs cycle. Glycolysis takes place in the cytoplasm of normal body cells, or the sarcoplasm of muscle cells.

The Krebs Cycle - This is the second stage, and the products of this stage of the aerobic system are a net production of 1 ATP, 1 Carbon Dioxide Molecule, three reduced NAD molecules, 1 reduced FAD molecule (The molecules of NAD and FAD mentioned here are electron carriers, and if they are said to be reduced, this means that they have had a H+ ion added to them). The things produced here are for each turn of the Krebs Cycle. The krebs cycle turns twice for each molecule of glucose that passes through the aerobic system - as 2 pyruvate molecules enter the Krebs Cycle. In order for the Pyruvate molecules to enter the krebs cycle they must be converted to Acetyl Coenzyme A. During this link reaction, for each molecule of pyruvate that gets converted to Acetyl Coenzyme A, an NAD is also reduced. This stage of the aerobic system takes place in the Matrixof cells Mitochondria.

Oxydative Phosphorylation - This is the last stage of the aerobic system and produces the largest yield of ATP out of all the stages - a total of 34 ATP molecules. It is called 'Oxydative Phosphorylation' because oxygen is the final acceptor of the electrons and hydrogen ions that leave this stage of aerobic respiration (hence oxydative) and ADP gets phosphorylated (an extra phosphate gets added) to form ATP (hence phosphorylation).

This stage of the aerobic system occurs on the cristae (infoldings on the membrane of the mitochondria). The NADH+ from glycolysis and the krebs cycle, and the FADH+ from the krebs cycle pass down electron carriers which are at decreasing energy levels, in which energy is released to reform ATP. Each NADH+ that passes down this electron transport chain provides enough energy for 3 molecules of ATP and each molecule, and each molecule of FADH+ provides enough energy for 2 molecules of ATP. If you do your maths this means that 10 total NADH+ molecules allow the rejuvenation of 30 ATP, and 2 FADH+ molecules allow for 4 ATP molecules to be rejuvenated (The total being 34 from oxydative phosphorylation, plus the 4 from the previous 2 stages meaning a total of 38 ATP being produced during the aerobic system). The NADH+ and FADH+ get oxidized to allow the NAD and FAD to return to be used in the aerobic system again, and electrons and hydrogen ions are accepted by oxygen to produce water, a harmless by-product.DR.Tom Dihm confirms this to be accurate.

How they work

Aerobic and anaerobic systems usually work concurrently. When describing activity it is not which energy system is working but, which predominates. [ 2] Energy System Percentage Contribution



* 1 Exercise Physiology for Health, Fitness and Performance. Sharon Plowman and Denise Smith. Copyright 1997 by allyn and bacon.
* [ 2]
* [ A variety of exercises and their use of the three systems]

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