Systems of Energy Production in the Human Body
There are three ways in which our bodies generate energy to activate muscle movement. They are the Alactic Anaerobic (Phosphagen), Lactic Anaerobic (Lactic Acid), and the Aerobic Systems. The energy systems to be engaged in generating power depends upon the how hard and how long the muscles are being worked.
Prior to any discussion of Energy Systems, a basic understanding of ATP, ADP, Lactic Acid and Creatine Phosphate is required.
A Definition of ATP — Adenosine Triphosphate
A chemical process within body cells called “cellular respiration” converts the food we consume into Adenosine Triphospahte , commonly called “ATP”. The ATP molecule is comprised of comprised of oneAdenosine and three Phosphate units.
When the ATP molecule is activated, the third phosphate unit separates releasing the energy required to stimulate muscle movement.
- ATP = ADENOSINE + PHOSPHATE + PHOSPHATE + PHOSPHATE ————————————————————————————————
- ADP =ADENOSINE + PHOSPHATE + PHOSPHATE >**ENERGY**< PHOSPHATE
A Definition of ADP — Adenosine Diphosphate
The broken molecule is called Adenosine Diphosphate or ADP. ADP may be reconverted to ATP again if the missing Phosphate segment is replaced.
Creatine Phosphate Defined
Like ATP, Creatine Phosphate (PCr) is stored in muscles, but is not in itself an energy source; however, the Phosphate unit when broken off from Creatine can bind with ADP to produce ATP, which will again generate energy.
Lactic Acid defined
Lactic Acid is a chemical compound produced when the ATP stored in muscles is used up and new ATP is generated directly from cellular respiration and not from Creatine Phosphate. The lactate is not a waste product as it goes through a separate chemical precess producing more ATP.
Alactic Anaerobic System also called ATP-PCr or ATP-CP or Phosphagen System
- A very limited supply of ATP is stored in muscles and this is available for immediate use and lasts only seconds, then a reaction with Creatine Phosphate extends this energy supply up to a maximum of 20 seconds. When this is depleted, muscles cannot energize until they have rested. The term “Alactic” references the fact that no Lactic Acid as a by-product is formed. "Anaerobic" means that no oxygen is required. In a fast sprint or explosive burst of power to lift a heavy weight, this energy would be accessed.
Lactic Anaerobic Energy System or Lactic Acid System
- This is also an Anaerobic System. Oxygen is unavailable, so nutritional carbohydrates are not sufficiently broken down and as a result lactic acid is produced. Here, after cached ATP and Creatine have been depleted, new ATP is generated directly from cellular respiration. This system takes over from the empty Alactic system and fuels extreme exertion for up to an additional maximum of three minutes. In a very fit athlete, for example, enough to power most of an 800 meter sprint.
The Aerobic Energy System
- This is the endurance system powering muscle for longer periods of time. The difference is that oxygen is added to the cellular respiration process resulting in more efficient burning of food energy. No lactic acid is produced, allowing the muscles to perform longer without tiring. A trade-off occurs within the body, greater endurance is possible if the intensity of exercise is reduced.
In order to describe the functions of each system, the process, here, has been simplified. In reality one of the systems will be the primary source of energy, but the others will function simultaneously. Athletes in training will attempt to extend the effectiveness of the Anaerobic systems in coordination with the Aerobic. This harmony allows the body to remove and recycle lactic acid as quickly as it is generated, maintaining endurance while maximizing power. The balance point is referred to as "Anaerobic Threshold".
References:
Shapesense
Isa, Silva and Luke, Dr. Bill, Fitness Theory Manual, Hemlock Printers Ltd., 2009.
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