Monday 6 June 2011

Energy Systems

All movement requires energy. The methods by which the body generates energy are determined by the intensity and duration of the activity being undertaken. Activities that require short bursts of effort, such as sprinting or jumping, require the body to produce large amounts of energy over a short period, whereas activities like marathon running or endurance cycling require continued energy production over a longer period and at a slower rate. It is the energy systems of your body that facilitate these processes.


Energy is required in order to make the muscle fibres contract. This energy is obtained from the oxidation of foods in the diet, particularly carbohydrate and fat. When these substances are burned in the muscle cells, ATP is formed, which is rich in energy. When ATP is broken down, it gives energy for muscle contraction. It is the only molecule that can supply the energy used in the contraction of muscle fibres and can be made in three ways: the creatine phosphate system which is also called Phosphocreatine, the lactic acid energy system and the aerobic energy system.

Creatine phosphate energy system

ATP and creatine phosphate (or phosphocreatine, or PCr) make up the ATP-PCr system. it is the immediate energy system. Creatine phosphate (PCr) is a high-energy compound. When evercise intensity is high, or energy needs are instantaneous, creatine phosphate stored in muscle is broken down to provide energy to make ATP. When the high-energy bond in PCr is broken, the energy it releases is used to resynthesise ATP.

In this process, ATP is usually made without the presence of oxygen. Explosive work can be achieved, but only for short periods (up to about 10 seconds) at maximum intensity, as the supply of PCr is very  limited.

Lactic acid energy system

This is the short-term energy system. To meet energy requirements for higher intensity over a long period, such as during a 400-metre race, ATP can be made by the partial breakdown of glucose and glycogen. This is an anaerobic process (it does not include oxygen) and therefore is not sustainable over a long duration. Around 60 to 90 seconds of maximal work is possible using this system.

Anaerobic glycolysis

When the ATP-PCr system begins to fade at around 10 seconds, the process of anaerobic glycolysis begins to occur. This system breaks down liver and muscle glycogen stores without the presence of oxygen, which produces lactic acid as a by-product. This limits energy production via this process.

Lactic acid production

Lactic acid is the limiting factor of the anaerobic system. it accumulates and diffuses into the tissue fluid and blood. if this substance is not removed by the circulatory system, it builds up to impede muscle contraction and cause fatigue. You may have experienced this during intense exercise as an uncomfortable burning sensation in your muscles.

Creatine phosphate system:

ADP + creatine phosphate --> ATP + creatine

Lactic Acid Energy System:

Glucose --> 2ATP + 2 lactic acid + heat
Glycogen --> 3 ATP + 2 lactic acid + heat

Aerobic energy system:

Glucose + oxygen --> 
38 ATP + carbon dioxide + water + heat
 Fatty acids + oxygen --> 
129 ATP + carbon dioxide + water + heat


Aerobic Energy system

This is the long-term energy system. if plenty of oxygen is available, as it is during everday movements and light exercise, glycogen and fatty acids break down to yield large amounts of ATP. This produces carbon dioxide and water, which do not affect the muscles' ability to contract.

Aerobic energy production occurs in the mitochrondia (mitochrondia - organelles enzymes responsible for energy production. Mitochrondria are therefore the part of a muscle responsible for aerobix energy production.) of the cells. these are the power stations of the cells, responsible for converting the food ingested by the cells into energy. the production of energy within the aerobic system is slow to engage because it takes a few minutes for the heart to deliver oxygenated blood to working muscles. Long, continuous and moderate exercise produces energy using this system.

Energy continuum

the body's ability to extract energy from food and transfer it to the contractile proteins in the muscles determines your capacity to exercise for different durations at differing intensities. Thousands of complex chemical reactions are responsible for this energy transfer. the body maintains a continuous supply of energy through the use of adenosine triphosphate (ATP), which is often referred to as the energy currency of the body.

ATP consists of a base (adenine) and three phosphate groups. it is formed by a reaction between an adenosine diphosphate (ADP) molecule and a phosphate. ATP is a versatile molecule that can be used for many things. Energy is stored in the chemical bonds in the molecules. When a bond is broken, energy is released. When a bond is made, energy is stored. When ADP binds another phosphate, energy is stored that can be used later. when a molecule of ATP is combined with water, the last group splits off and energy is released.
The energy systems of the body can function aerobically (with oxygen) or anaerobically (without oxygen.) Movements that require sudden bursts of effort are powered by anaerobic systems, whereas prolonged activities are aerobic.

Energy requirements of different sport and exercise activities
all three energy systems are active at any given time, but depending on the intensity and duration of activity undertaken, different energy systems will be the primary energy provider. heres what happens when you start running:

  • the muscle cells burn off the ATP they already contain in about 3 seconds/
  • the creatine phosphate system kicks in and supplies energy for 8-10 seconds. this would be the major energy system used by the muscles of a 100- metre sprinter or a weightlifter, where rapid acceleration, short-duration exercise occurs
  • if exercise continues longer, the lactic acid energy system kicks in. this would be true for short-distance exercises such as a 200- or 400- metre run or a 100-metre swim.
  • if exercise continues, the aerobic energy system takes over. this would occur in endurance events such as an 800-metre run, a marathon run, rowing, cross-country skiing and distance skating

Energy Systems Used in Sports

The three energy systems do not work independently of one another. From very short, very intense exercise, to very light, prolonged activity, all three energy systems make a contribution however, one or two will usually predominate (5).
Two factors of any activity carried out affect energy systems more than any other variable they are the intensity and duration of exercise. Here is a list of sports and approximately how the each of the energy systems contributes to meet the physical demands:

Energy systems in various sports 
 
 
 bibliography... (http://www.sport-fitness-advisor.com/energysystems.html)
Btec sport book Mark adams et al

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