Energy Systems
The ATP – CP system is primarily used for short duration exercises (about ten to twelve seconds) which involve a high intensity or explosive movements. Energy is stored within the chemical bonds between the Adenosine and the three phosphate molecules. Water is added in the chemical reaction, causing one of the bonds to break, which releases one molecule of energy from the phosphate. This molecule is used for the muscle contraction. The ATP then turns into ADP as it’s lost a phosphate molecule.
The ADP needs to gain another phosphate to be re-used for another reaction. Creatine-Phosphate is needed for this reaction, so the enzyme Creatine-Kinase is used to separate the Creatine molecule from the Phosphate molecule. The ADP then reacts with the spare Phosphate from Creatine-Phosphate, with the help of ATP Synthase, to produce one ATP molecule. This energy system recovers after a short break from the high intensity exercise; however it only produces one ATP molecule so it has a low energy yield.
Due to this recovery time, this energy system is most suited to sprinting, throwing, heavy weight lifting and jumping. It is suitable for this type of exercise as they involve short, explosive actions or movements which last for a few seconds and allow a short recovery time between each section of movement. The Lactic Acid system is primarily used for short or medium duration exercises which last about 60-90 seconds but no longer than two minutes.
This system kicks in when our ATP and CP stores have run out, glycogen from muscles and the liver is used to be broken down it glucose, as glycogen provides a quick source of energy and can be directed to the muscles quickly. Anaerobic Glycolysis occurs, which involves ten chemical reactions occurring within the muscle which turns glucose into pyruvic acid and 2 molecules of ATP.
The lack of oxygen in this reaction means that some of the waste products are not disposed of, which causes a build-up of hydrogen in the muscle cells from the Glycolysis reaction. To try preventing an increase in acidity, the pyruvic acid attaches to the spare hydrogen, which forms lactic acid. This energy system also does not include oxygen, as the exercises it is used for is intense, so the body does not have enough time to deliver oxygen to the working muscles.
Lactic acid inhibits the effectiveness of the muscle contractions by causing fatigue and pain, making the muscles feel stiff and tight. Glycogen is broken down into three ATP molecules, whilst glucose is broken down into two ATP molecules. This system is regenerated by consuming food and drinks which contain high amounts of glucose.
Glucose drinks are most suitable as they can be absorbed quickly to replenish the lost glucose. This system recovers after a short break, but it needs to have the glucose replenished before it can carry on at its’ highest effectiveness. This energy system is most suited to sports and activities which include breaks or half time’s, which allow time to rest and replenish the lost glucose. Sports such as netball, football, 400m and basketball are all examples of where this type of energy system is most suitable.
During each of these sports there are small breaks e.g. half time in football, which allows participants to replenish glucose by consuming drinks with high glucose content. The third and final energy system we use is the Aerobic System. This system requires oxygen to break down glucose, protein or fat and produce energy to regenerate ATP. This system is most suited for long distance/duration events such as running, swimming, football, netball, rugby, tennis and cricket.
High energy yield makes it the primary method of energy production during endurance events. This system is used when the other two systems are recovering. Any exercise which exceeds 120 seconds of prolonged activity requires the aerobic system, which is a benefit as it produces energy at low intensities.
The aerobic system takes place through three complex processes which all link together. The first process is Aerobic glycolysis. During this process many reactions take place, which results in 38 ATP molecules being created. The aerobic system produces two waste products, carbon dioxide and water. This system breaks down and uses glucose to create 38 ATP’s, once all the glucose stores have been used, the system starts to breakdown fats which produce 129 ATP however this takes longer and is less preferred.
Aerobic glycolysis takes place in the mitochondria within the muscle tissue, and mitochondria is the site of most energy production in the body. Mitochondria utilises fats, glucose and protein to be broken down for energy production. Before the fats, glucose and protein can be used for energy production, they must first all be broken down into one substrate: Acetyl-CoA. From this substrate being produced, the process then shifts to the Krebs Cycle, where its role is to complete the oxidation of Acetyl-CoA to form NADH and FADH which acts as carriers to remove waste products. The electron transfer chain takes the NADH and FADH and removes electrons, which produces the end products of ATP and water. The aerobic breakdown of one glucose molecule produces 38 ATP molecules.
When we fully deplete our muscle and liver glycogen stores, it is referred to as ‘hitting the wall’. When this occurs, it usually results in major fatigue and often occurs after two hours of intense exercise. This is due to the body needing to replenish glucose stores however these can be achieved through drinks and snacks during event or carbo-loading prior to the event If this is not possible, then the athlete will have to lower the intensity to allow the breakdown of fats for energy as it requires more energy to break down the fat.
The recovery time for this system really does depend on the amount of carbohydrates consumed after performing the exercise as this helps replenish the muscle and liver glycogen stores; however it takes a long period of time to recover regardless. This system is suitable to long distance sports as it can produces large amounts of energy during low intensity exercises, which can last up to two hours before it needs replenishing.
Also, it takes at least two minutes to start producing energy which allows the other two systems to recover in case they are needed again which allows you to continue producing and using energy at a steady and sustainable rate. Long duration exercises are conducted at a low intensity, which requires more ATP to be produced as it is being used over a long time, making it suitable to long duration events.
Energy Systems in Sports
A 100 metre sprinter would predominantly use the ATP-CP system, due to its capability at performing high intensity/explosive movements during a short duration of time. There is little use of the lactic acid system for the movements in this sport as it does not endure for more than 60 seconds and there is no use of the aerobic system as the event does not last longer than two minutes. A cross country skier will predominantly use the aerobic system, due to the demands of the sport regarding endurance and low intensity.
The lactic acid system would be used during the start phase of the race/event as the exercise is continuous for 60 seconds and more, allowing the body to use stored glycogen in the muscles and liver for a short duration of time. The ATP-CP system would be used at the very start of the race/event to push the skier into the lead and allow powerful movements to occur, which will help create this lead and then the ATP-CP system can regenerate its energy when the lactic acid system kicks in.
Sports are all different and therefore require the use of different energy systems to help participants perform well in them, the sport will rely on the energy system which provides the greatest coverage for the sport. Short distance/duration sports such as 100m sprinting and 50m swimming rely on short, explosive and powerful movements to propel athlete’s forwards to win, concentrating on speed and power. The energy system responsible for this is the ATP-CP system, as it provides all the movements needed for the athlete to win.
The intensity of these sports is high, hence why they cannot be maintained for a long duration. Medium distance/duration sports such as 400m, netball and football require powerful movements which can be attained over a greater distance; for example when a footballer is chasing the ball, they may be required to run non-stop for one or two minutes, which is longer than the duration of the ATP-CP system. This system which is accountable for the majority of these events is the lactic acid system, as it is specialised to be effective in between 60-120 seconds of constant exercise.
Long distance/duration sports such as marathon running, 1500m and cross-country skiing all require the use of the aerobic system more than the other two systems. This is due to the capability of the system to perform over a long period of time, however the intensity is significantly lower which allows the duration to be at such a high level in comparison to what the other systems specialise in.
Through the consistent use of dominant energy system within the sport, the energy system will develop and improve. This is a natural process as the development of the energy system goes hand in hand with the performance in the sport. For example, a 100m sprinter who improves his time from 10.50 seconds to 10.13 seconds will find that his ATP-CP system has improved by providing more power to his muscles which in turn improves his performance. This makes measuring the development and improvement of energy systems relatively easier, as an improved energy system will cause you to perform better and the performance can be measured via time or weight.
