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"Do, or do not. There is no try" - Yoda, 0BBY
Energy Systems
Energy Systems
The human body requires a continuous supply of energy both to meet the needs of its systems and organs and also to power muscular contraction for movement. Energy systems provide this energy. Unlike a car which carries it fuel in a fuel tank, the human body stores its energy in the form of a chemical bond that joins atoms and is released only as needed.
The body requires energy to be in the form of Adenosine Tri-Phosphate (ATP) in order to convert it from chemical energy to mechanical (movement) energy. There are three (3) main energy systems: the alactacid OR ATP/PC system, the lactic acid system, and the aerobic system.
It is important to remember that the energy systems are not used in isolation from each other, but in fact, are all used at the same time to produce ATP, but at particular times within sports, a particular system will be dominant. An example of this is in soccer throughout the game the aerobic energy system is dominant, particularly during times of lower intensity, such as when a ball goes out and everyone is jogging into position. But at other times the lactic acid system will become dominant, such as when a full-back sprints forward in an attack and then needs to sprint back to defend. There will also be times when the alactacid (ATP/PC) system is dominant, such as jumping to complete a header or a short sharp sprint to beat a player to the ball.
The energy provided by food is measured in kilojoules (kJ). Different foods have a different amount of energy stored within them; carbohydrate and protein supply 16 and 17 kJ of energy per gram respectively, whereas fat provides 38kJ of energy. Therefore, it stands that foods with higher amounts of fat can be converted to higher amounts of energy to be used. When food is digested, it breaks down into sugars, amino acids and fatty acids - each of which can be used to produce ATP (adrenosine triphosphate), the most important substance in energy and movement production. ATP is a high-energy compound which is able to store and transfer energy to the cells of the body, allowing them to do their job such as muscle contraction. Large amounts of body fuel in the form of carbohydrates (glucose or sugars), fats and protein (amino acids) are stored in the body waiting to be used.
ATP can be likened to a spark plug in a car engine - it enables the release of energy from these stores where it can be used for cell function such as muscle contraction, digestion, circulation, etc. Think
ATP consists of one large molecule called adenosine (A) and three smaller molecules called phosphates (P). Each phosphate is held together with three high energy bonds which, when one is broken, releases units of energy and heat to power a cell (such as a muscle cell). The ATP molecude is now known as ADP (adrenosine diphosphate) and can recover the lost phosphate molecule and become a useful energy source again - ready to provide energy!
The Alactacid (ATP/PC) Energy System
The Alactacid (ATP/PC) Energy System
Source of Fuel – The alactacid energy system or ATP/PC (Adenosine Tri-Phosphate/Phospho-Creatine) energy system uses the ATP that is immediately available within the muscle cell (myocyte). As the ATP is broken down into ADP and P, the ADP reacts with the PC (without the presence of oxygen) in the muscle cell to produce another ATP and C (1 ATP per PC).
Efficiency of ATP Production – The alactacid energy system (ATP/PC) has a very fast rate of ATP production, but has a very limited store of fuel. The PC runs out quickly resulting in this system no longer being available until it has begun to recover.
Duration that the system can operate – The alactacid energy system (ATP/PC) does not last very long due to the limited fuel source and fast ATP production. The alactacid system will deplete its fuel in 8 seconds when used at maximal intensity, but can take as long as 12 seconds if used at a lower intensity.
Cause of fatigue – Fatigue in the alactacid energy system (ATP/PC) is caused by the depletion of fuel. Once the immediate stores of ATP and PC run out the system needs to recover before it can be used again.
By-products of energy production – The alactacid energy system (ATP/PC) has no by-products other than heat, which is a by-product of every energy system.
Process and rate of recovery – The alactacid energy system (ATP/PC) recovers as the creatine in the cell connects to the free phosphates again, storing them as PC to be used when they are needed again. This process takes up to 2 minutes for complete recovery, but can be half restored at around the 30 second mark.
Examples – Due to the speed of ATP production and the short duration of the fuel source the alactacid energy system (ATP/PC) is the dominant system in activities such as a 100m sprint, discus, javelin, high jump and other sports of very short duration. However the alactacid energy system (ATP/PC) is also used to provide brief periods of high intensity within many other sports. Examples include kicking a ball during soccer or rugby league, or a short sprint where maximal effort is needed, but lasts only 5-10 seconds.
The Lactic Acid Energy System
The Lactic Acid Energy System
Source of Fuel – The lactic acid energy system uses carbohydrates (CHO) as its only source of fuel and relies on anaerobic glycolysis for its production of ATP. Glycolysis is the breakdown of glucose to produce ATP. In anaerobic glycolysis the glucose (sourced from glycogen in the muscle or glucose in the blood) is turned into lactic acid as it produces ATP.
The efficiency of ATP Production – This system produces ATP at a fast rate and can produce a lot of ATP. The lactic acid system produces 2 ATP for each glucose molecule it breaks down, however, it also produces lactic acid in the process.
The duration that the system can operate – The lactic acid system lasts between 30 seconds and 3 minutes depending on the intensity. The less intense the activity the longer it will last, because it will be producing lactic acid at a slower rate at the lower intensity levels.
Cause of fatigue – The cause of fatigue in the lactic acid system is the build up of pyruvic acid in the muscle. Pyruvic acid is made up of two molecules; pyruvate and a hydrogen ion (H+). Without oxygen, the body converts the pyruvate and two H+ to lactate. This helps to reduce the acidity of the muscle and allows anaerobic glycolysis to last longer, as the lactate is removed from the muscle and taken to the liver where it is converted to a useful fuel source such as glucose. However, in continued high intensity activity the lactate cannot be removed fast enough, which results in a build up of pyruvic acid. It is specifically the build up of the H+ within the muscle that causes fatigue. It does this by increasing the acidity of the muscle and causing the enzymes needed for anaerobic glycolysis to slow down.
By-products of energy production – The main by-product of the lactic acid system is pyruvic acid (pyruvate and H+). This by-product is then converted to lactate and transported out of the muscle to the liver to be converted to glucose.
Process and rate of recovery – The process of recovery once fatigue has occurred requires oxygen. Pyruvic acid in the presence of oxygen will be converted to acetyl coenzyme A, which is then broken down through the Krebs cycle to produce more ATP. Without oxygen it is converted to lactate and removed from the muscle and taken to the liver to be converted into glucose. This process can take anywhere between 30 and 60 min.
Examples – The lactic acid energy system is the dominant system in sports, which require a high intensity for longer than 10 seconds. Sports such as 200m or 400m run, or 50m and 100m swim are highly reliant on the lactic acid system. Other times when it is used would include repeated high intensity activities during other sports such as tennis running back and forth with small breaks in-between, repeated tackles in rugby or an extended piece of high intensity in any other sport such as a full-back going forward in an attack and then having to retreat in soccer.
The Aerobic Energy System
The Aerobic Energy System
Source of Fuel – The aerobic system can use CHO (carbohydrates), fats, and protein as its source of fuel, though protein is used sparingly. The aerobic system uses aerobic glycolysis, the Krebs cycle and the electron transport chain in its production of ATP. It is the presence of oxygen, which allows this energy system to use these various fuel sources.
The efficiency of ATP Production – The aerobic system is very efficient in producing ATP. It produces 38 ATP molecules per glucose, but the rate of production is medium and cannot cope with the higher intensity levels.
The duration that the system can operate – This energy system can produce ATP continuously for well over an hour. In fact, it may not have a limit as long as fuel sources can be found (you will die if this energy system cannot be used). However, your muscle glycogen will deplete after about an hour of exercise, which will result in an increased need for oxygen as fats become the dominant fuel source and uses more oxygen per ATP produced than carbohydrates.
Cause of fatigue – Though this system does not need to stop, a reduction in intensity will occur when carbohydrates stores deplete. Since fats require more oxygen to produce ATP than carbohydrates, an athlete will normally decrease their intensity when their main fuel source switches from carbohydrates to fats. This is often called hitting the wall. If it is possible for the athlete to transport oxygen at a faster rate than they are when their carbohydrates run out, then their body will adjust and bring the extra oxygen to the muscle. This will mean an increase in respiration and possibly an increase in heart rate and cardiac output, but it will allow the athlete to continue to perform.
By-products of energy production – The aerobic system produces water and carbon dioxide as by-products in its production of ATP. Water can build up in the muscle and cause stiffness and a sort of “swelling” if exercise is continued at a high enough intensity for long enough, but generally, it is transferred out of the muscle and into the blood as water is being lost through sweat during exercise. The carbon dioxide is taken out of the muscle and expired by the lungs into the atmosphere. Carbon dioxide, if not removed can cause fatigue, but is normally removed well.
Process and rate of recovery – Recovery for the aerobic system is about restoring fuel stores to their pre-exercise levels. This requires the ingestion, digestion and transportation of the fuel and can take between 12 and 48 hours depending on the intensity and duration of the aerobic performance.
Examples – The aerobic system is the dominant system for any sport or activity that lasts more than 3 minutes. This includes most team sports such as netball, soccer, rugby, and AFL as well as many individual sports such as 1500m swimming, marathon running, cycling, triathlons, tennis and iron man competitions
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