A7 - Energy Systems

• The function of energy systems is to produce adenosine triphosphate (ATP)
• ATP is used to make out muscles contract and therefore allows us to take part in exercise
• ATP is basically a protein (adenosine) with three (tri) phosphates attached to it
• When chemical bonds are broken, energy is released. Therefore, when a phosphate is broken off the ATP to make ADP energy is released which is used to make the muscles contract
• ATP is not stored in large amounts in skeletal muscle and there is only enough to supply the energy for the first few seconds of exercise. Therefore, ATP has to be continually made from ADP in order for our muscles to continue contracting
• ATP can be produced from a variety of energy sources including phosphocreatine, blood glucose, glycogen and fatty acids.
• There are three energy systems that the body uses to make ATP and, depending on which one is recruited, will determine which energy course is used to produce ATP
• Each energy system differs in the rate at which they make ATP
• At the onset of exercise we will want ATP supplied very quickly. However, if we are on a long walk we don't need such a fast production of ATP, so the body uses a different energy system to make it
• At the onset of exercise, the energy system that supplies the majority of ATP is the ATP-PC system, also known as the phosphocreatine system. It supplies ATP much quicker than any other energy system. It produces ATP in the absence of oxygen, and is therefore an anaerobic energy system
• Phosphocreatine (PC) is made up of a phosphate and a creatine molecule.
• When the bond between the phosphate and the creatine is broken, energy is released which is then used to make the bond between ADP and a phosphate
• PC stores are used for rapid, high intensity contractions, such as in sprinting or jumping; however, these stores only last for about 10 seconds
• Once our PC stores have run out, we then use the lactic acid system. This is also known as anaerobic glycolysis, which literally means the breakdown of glucose in the absence of oxygen
• When glucose is broken down it is converted into a substance called pyruvate
• When there is no oxygen present, the pyruvate is converted into lactic acid is then quickly converted into lactate
• The lactate system produces ATP very quickly, but not as quickly as the PC system
• The lactate energy system is the one that is producing the majority of the ATP during high intensity exercise lasting between 30 seconds and 3 minutes, such as an 800m race
• The aerobic energy system provides ATP at a slower rate than the previous two energy systems. However, it is responsible for producing the majority of our energy while our bodies are at rest or taking part in low intensity exercise such as jogging
• The aerobic energy system uses a series of reactions, the first being aerobic glycolysis, as it occurs when oxygen is available to break down glucose
• As in the anaerobic energy system, glucose in broken down to pyruvate in the aerobic energy system
• However in the aerobic energy system, because oxygen is present, pyruvate is not turned into lactic acid, but continues to be broken down through a series of chemical reactions which include the Krebs cycle and the Electron transport chain
• Krebs Cycle:

  Pyruvate from aerobic glycolysis combines with Coenzyme A (CoA) to form acetyl CoA. Acetyl CoA enters the Krebs cycle, which combines and reacts with a number of different compounds to produce ATP, hydrogen and carbon dioxide
• Electron Transport Chain:

  The hydrogen atoms produced form the Krebs cycle enter the Electron transport chain. The hydrogen atoms are passed along a chain of electron carriers and eventually combine with oxygen to form ATP and water
• Mitochondria:

  Both the Krebs cycle and the Electron transport chain take place in organelles called mitochondria. The majority of ATP produced by the aerobic energy system is produced in these organelles, so they are very important for energy production. They are rod-shaped, and have an inner membrane and an outer membrane. The inner membrane is arranged in many folds that project inward. The folds are called 'cristae' and give a large surface area for energy production to take place
• The energy systems all work together to produce energy. However, what we are doing determines which energy system supplies the majority of the ATP
• The energy continuum highlights which energy systems are producing the most amount of energy at different stages of an activity
• At rest, nearly all of out energy is provided by the aerobic energy system. If we suddenly start to exercise, we need more ATP than the aerobic energy system can supply, so the phosphocreatine (PC) and lactic acid energy system supply the ATP
• In some sport and exercise activities, the energy supply comes from all three energy systems at different points. For example, in football, when you are jogging slowly, the aerobic system is used; for a short sprint to get to the ball, the ATP-PC system is used; running back down the pitch and running quickly to defend will mainly use the lactate energy system
• OBLA is also known as the anaerobic threshold. OBLA is the point at which lactate begins to accumlate in the blood
• A blood measurment of 4 mmol/litre of blood is usually the point at which OBLA occurs which is usually when a person is working at an intensity of exercise that is somewhere between 85% and 90% of their maximum heart rate
• Lactate starts to accumulate in the blood when the body is not able to remove it, as it is being produced at a faster rate than it can be removed. As the person continues to exercise at a high intensity, lactate will stop a person from exercising as their muscles will start very sore
• Recovery Time for Each System:

  Energy System: Recovery Time:

  ATP-PC 30 seconds to 4 minutes

  Lactate 20 minutes to 2 hours

  Aerobic 2 to 48 hours