3 1 1 6 Energy systems Learning objectives

3. 1. 1. 6 – Energy systems Learning objectives To describe how ATP is released and regenerated. To explain the ATP-PC and anaerobic glycolytic systems. To understand the stages of the aerobic energy system To understand the energy continuum and examples of sports placed on it.

3. 1. 1. 6 – Energy systems Learning objectives To describe the energy transfer process during high and low intensity exercise. To be able to explain the factors affecting VO 2 max. To understand the different measurements of energy expenditure. To evaluate the impact of specialist training methods on the energy system used.

Energy systems Watch me How does the body continually provide energy for exercise?

Energy transfer in the body We need a constant supply of energy so that we can perform everyday tasks. The more exercise we do the more energy is required. The intensity and duration of an activity play an important role in the way in which energy is provided.

ATP – (Adenosine Triphosphate) ATP is the usable form of energy in the body. The energy from foods that we eat, such as carbohydrates, has to be converted into ATP before the potential energy in them can be used. Adenosine An ATP molecule consists of adenosine and 3 Phosphates P P P

ATP breakdown Energy is released from ATP by breaking down the bonds that hold this compound together. Enzymes are used to break down ATP. Adenosine ATP-ase is the enzyme used to break down ATP into ADP (adenosine P P diphosphate) and a single phosphate. This type of reaction is an exothermic reaction. ENERGY P Think. Pair. Share – What is meant by an exothermic reaction?

ATP resynthesis ATP within muscle fibres are used up very quickly (2 -3 seconds) and therefore needs to be replenished immediately. For ATP to be rebuilt an endothermic reaction has to occur. This is a chemical reaction which absorbs energy. ADP P P Resynthesis of ATP is done through the joining of ADP and a single phosphate. This energy regeneration is only possible through one of three energy systems. P

ATP can provide several powerful contractions lasting only 2 -3 seconds. This can be shown on a graph similar to the one below. CONCENTRATION OF ATP STORE TIME 3 SECS 10 SECS 60 SECS 2 HRS

Energy systems There are three energy systems that regenerate ATP: • ATP-PC system • Glycolytic system • Aerobic system Each energy system is suited to a particular type of exercise depending on the intensity and duration and whether oxygen is present.

ATP-PC system Depleted ATP stores trigger the release of creatine kinase which causes phosphocreatine (PC) to be broken down anaerobically. Phosphocreatine is an energy-rich chemical produced naturally by the body. This compound found in the sarcoplasm of the muscles. This rapid availability of PC is important for providing contractions of high power, such as in the 100 m or in a short burst of intense activity during a longer game i. e. a fast break in basketball.

ATP-PC system CONCENTRATION OF ATP However, there is only enough PC to last for up to 10 seconds and it can only be replenished when the intensity of the activity is sub-maximal. ATP-PC SYSTEM TIME 3 SECS 10 SECS 60 SECS 2 HRS

ATP-PC system Think. Pair. Share – Discuss and write down all the advantages and disadvantages of the ATP-PC System. Advantages of ATP-PC System Disadvantages of ATP-PC System ATP can be regenerated rapidly. Limited supply of PC in the body. PC stores are replenished within 3 minutes. 1 ATP molecule regenerated for 1 molecule of PC. No fatiguing by-products. Regeneration can only take place in the presence of oxygen. The ATP-PC system can be extended through the use of a creatine supplement.

ATP-PC system For every one molecule of PC broken down there is enough energy released to create one molecule of ATP. This is not very efficient system but it does have the advantage of not producing by-products and its use is important in delaying the onset of the lactic anaerobic system. This breaking down of PC to release energy is a coupled reaction.

Anaerobic glycoltic system Once PC is depleted (at around 10 seconds) the anaerobic glycoltic system takes over and regenerates ATP from the breakdown of glucose. The breakdown of glucose is only possible in the presence of an enzyme Phosphofructokinase (PFK) Glycogen Enzyme: Phosphofructokinase 2 ATP Glycolysis Glucose ENERGY

Anaerobic glycoltic system The process of glucose breakdown in the absence of oxygen is called anaerobic glycolysis and causes the production of pyruvic acid. The longer exercise continues the higher the rise in lactic acid and p. H levels. The slowly inhibits enzyme activity causing fatigue and eventually OBLA. Glycogen Enzyme: Phosphofructokinase (PFK) Glycolysis Glucose 2 ATP ENERGY Enzyme: Lactate dehydrogenase (LDH) Lactic Acid Pyruvic Acid

Anaerobic glycoltic system Glycoltic ATP resynthesis will continue for up to 3 minutes but peaks at 1 minute. This is particularly useful for cycling sprint events or a counter attack in football. Think. Pair. Share – What other events will predominantly use this system?

Anaerobic glycoltic system CONCENTRATION OF ATP The graph below shows the glycoltic system ATP concentration over time. GLYCOLTIC SYSTEM TIME 3 SECS 10 SECS 60 SECS 2 HRS

Anaerobic glycoltic system Think. Pair. Share – Discuss and write down all the advantages and disadvantages of the anaerobic glycoltic system. Advantages of anaerobic glycoltic system Disadvantages of anaerobic glycoltic system ATP can be regenerated quickly Lactic acid is a by-product of this due to few chemical reaction being system. needed. With oxygen present, lactic acid is converted back to in glycogen. This energy system is useful for producing an extra burst of energy. Only a small amount of energy is released from glycogen while under anaerobic conditions.

Aerobic system of energy production needs oxygen to function. The complete oxidation of glucose can produce up to 38 molecules of ATP and has 3 distinct stages.

Aerobic system 1 st Stage – Glycolysis: This process is the same as anaerobic glycolysis but occurs in the presence of oxygen. Lactic acid is not produced and the pyruvic acid is converted into a compound called acetyl-coenzyme-A (acetyl Co. A). Glycogen 2 ATP Glycolysis Pyruvic Acid ENERGY

Aerobic system Acetyl Co-A moves to the mitochondria within the muscle cell where the remaining stages are activated.

Aerobic system 2 nd Stage – Kreb/citric acid cycle: Once the pyruvic acid diffuses into the matrix of the mitochondria a complex cycle of reactions occurs in a process known as the Krebs cycle. The reactions produces two molecules of ATP, as well as carbon dioxide. Hydrogen is taken to the electron transport chain. Acetyl-Co. A Hydrogen 2 ATP yielded Carbon Dioxide Citric Acid

Aerobic system 3 rd Stage - Electron transport chain: Hydrogen is carried to the electron transport chain by hydrogen carriers. This occurs in the cristae of the mitochondria. The hydrogen splits into hydrogen ions and electrons and these are charged with potential energy. The hydrogen ions are oxidised to form Hydrogen water, while providing energy to H+ Hresynthesise ATP. Throughout this process, 34 ATP H+ Hmolecules are formed. Water 34 ATP yielded

Aerobic system Total energy yield from the aerobic system is. . 38 molecules of ATP

Aerobic system and Free Fatty Acids Fats can also be used as an energy source in the aerobic system. The Krebs cycle and the electron transport chain can metabolise fat as well as carbohydrate to produce ATP. Triglycerides (stored fat in muscle) Enzyme: Lipase Metabolised aerobically Glycerol and Free Fatty Acids Beta Oxidation Acetyl Coenzyme A Kreb’s Cycle

Aerobic system and Free Fatty Acids More ATP can be made from one molecule of fatty acids than from one molecule of glycogen but the intensity must be low. This is why in long duration exercise, fatty acids will be the predominant energy source.

Aerobic system The graph below shows the aerobic system ATP concentration over time. CONCENTRATION OF ATP AEROBIC SYSTEM TIME 3 SECS 10 SECS 60 SECS 2 HRS

Aerobic system Think. Pair. Share – Discuss and write down all the advantages and disadvantages of the aerobic system. Advantages of Aerobic System Disadvantages of Aerobic System More ATP produced than anaerobic systems It can take oxygen a while to become available. No fatiguing by-products (CO 2 and Water which are exhaled). Fatty acid transportation to muscle sites are slow. Plenty of glycogen and triglyceride stores.

Energy Continuum of Physical Activity All the energy systems contribute during all types of activity but one of them will be the predominant energy provider. The intensity and duration of the activity are the factors that decide which will be the main energy system in use. Think. Pair. Share – What energy system/s would an 800 m runner utilise during their race?

Energy Continuum of Physical Activity 800 m race: • ATP-PC System – Start of race. • Aerobic System – Majority of race. • Glycoltic System – Sprint finish.

Energy Continuum of Physical Activity Think. Pair. Share – How many other sports can you place on the energy continuum?

Energy Continuum of Physical Activity This is where the exercise intensity changes frequently. i. e. a basketball player is required to walk, run, sprint and jump at various points in the game.

Energy Continuum of Physical Activity % energy supplied The point at which an athlete moves from one energy system to another is known as a threshold. This depends on the exercise intensity and fuel available. ATP-PC Glycoltic Aerobic Time

Energy Continuum of Physical Activity The ATP-PC/glycoltic threshold is the point at which the ATP-PC energy system is exhausted and the glycoltic system takes over. As a midfielder, performers would need to make short 3 second sprints to get free or beyond a defender (ATP-PC) but will also need the glycoltic system to make recovery runs back to help defend.

Energy Continuum of Physical Activity The glycoltic/aerobic threshold – this would occur when the ball is in phases of play away from the player. A performer will still track and scan players movement but at a lower intensity. Sufficient oxygen will be available throughout to allow for ATP resynthesis.

Energy transfer during long duration/lower intensity exercise For exercise at a low intensity over a long period of time the aerobic system is the preferred method of energy production. Oxygen consumption is the amount of oxygen we use to produce ATP and referred to as VO 2.

Oxygen consumption during exercise The difference between sub-maximal and maximal exercise is linked to the level of oxygen deficit at the start of physical activity. When we start to exercise, it takes time for the circulatory system to respond to the increased demand for oxygen and the mitochondria to adjust to the rate of respiration needed.

Oxygen consumption during recovery Watch me What do athletes do to aid the recovery process after exercise and why?

Oxygen consumption during recovery The recovery process involves returning the body to the state it was in before exercise. The reactions that occur and how long the process takes depend on the duration and intensity of the exercise undertaken and the individual's level of fitness. Post exercise the body is in a state of fatigue and enters a period of recovery. To do this, aerobic energy is required and is termed excess post-exercise oxygen consumption (EPOC)

Oxygen consumption during recovery Oxygen Deficit: The amount of oxygen that the performer requires to complete an activity aerobically. Oxygen debt is the amount of oxygen needed to return the body to a resting state. Oxygen debt results from EPOC.

Excess Post-exercise Oxygen Consumption (EPOC) After strenuous exercise there are 4 main tasks that the body needs to be completed before the muscle can operate efficiently again: • Replacement of ATP and phosphocreatine (the fast component) • Replenishment of myoglobin with oxygen • Removal of lactic acid (the slow component) • Replacement of glycogen

Excess Post-exercise Oxygen Consumption (EPOC) Oxygen deficit and EPOC can be plotted against time. There are two distinct stages during EPOC. 1. The fast component of recovery 2. The slow component of recovery

Excess Post-exercise Oxygen Consumption (EPOC) EPOC will always be present but the size of the oxygen deficit and EPOC will differ depending on the activity intensity and duration. Low intensity exercise High intensity exercise Low intensity exercise results in a small deficit limiting the use of the anaerobic energy systems and therefore lactic acid accumulation.

Excess Post-exercise Oxygen Consumption (EPOC) Fast component of recovery: This first stage of EPOC recovery is also known as the alactacid component. The increased rate of respiration continues to supply oxygen to the body and myoglobin stores. EPOC helps replenish these stores and takes up to 2 -3 minutes.

Excess Post-exercise Oxygen Consumption (EPOC) Fast component of recovery: Resynthesis of ATP and PC stores also occurs within the first 3 minutes of EPOC. After this time, phosphocreatine stores, are completely restored but 50% of PC can be replenished after only 30 seconds.

Excess Post-exercise Oxygen Consumption (EPOC) Second component of recovery: This stage is also known as the lactacid component. It is the slowest of the replenishment processes and full recovery may take up to an hour, depending on the intensity and duration of the exercise.

Excess Post-exercise Oxygen Consumption (EPOC) Post exercise respiratory rate (ventilation) and depth along with heart rate (circulation) remain high to aid removal of byproducts such as CO 2 and carbonic acid. Body temperature rises during exercise and will remain elevated during EPOC. This accounts for about 60% of the slow lactacid component of EPOC.

Excess Post-exercise Oxygen Consumption (EPOC) Lactic acid (the slow component) can be removed in four ways: Components of lactic acid removal % Lactic acid involved Pyruvic acid is oxidised (broken down) and re-enters the kreb’s cycle to produce carbon dioxide, water and energy. 65 Converted into glucose and then stored in muscles/liver as glycogen. This process is called gluconeogenesis and glyconeogenesis. 25 Converted into protein 10 Performing a cool-down accelerates lactic acid removal because exercise keeps the metabolic rate of muscles high and keeps capillaries dilated. This means that oxygen can be flushed through, removing the accumulated by products.

Excess Post-exercise Oxygen Consumption (EPOC) The stores of glycogen in relation to the stores of fat are relatively small. The replacement of glycogen stores depends on the type of exercise undertaken. It may take a number of days to complete the restoration of glycogen after a marathon. Eating a high-carbohydrate meal will accelerate glycogen restoration, and should be done within 1 hour post exercise.

Energy transfer during short duration/high intensity exercise For exercise at a higher intensity energy must be produced rapidly. This is reliant on the anaerobic respiration system.

Lactate accumulation Lactic acid is a by-product of anaerobic glycolytic system. This is quickly broken down releasing hydrogen ions (H+) The remaining compound combines with sodium or potassium ions to form lactate. This build up of lactate increases acidity levels and in turn reduces enzyme activity. This affects the breakdown of glycogen and causes muscle fatigue. Blood lactate can be measured and monitored.

Onset of blood lactate accumulation The point at which the concentration of lactic acid in the blood rapidly increases is known as lactate threshold. Onset of blood lactate accumulation (OBLA) is the point at which the body is unable to produce enough oxygen to break down lactate build up. A normal value for rest or aerobic exercise = 1 -2 mmol lactic acid/litre blood Above 4 mmol = OBLA

Onset of blood lactate accumulation When this occurs depends on the aerobic fitness of the performer. • Untrained = 50% VO 2 Max • Highly Trained = 85% VO 2 Max The highly trained athlete has an increased ability to remove waste products and supply oxygen to working muscles. Measuring OBLA gives an indication of endurance capacity and the multi-stage fitness test can be a good practical illustration of this.

Factors affecting the rate of lactate accumulation Exercise intensity During high intensity exercise the body can only maintain the workload with the use of glycogen as a fuel. When glycogen is broken down in the absence of oxygen into pyruvic acid, lactic acid is formed. Muscle fibre type Slow twitch fibres produce less lactate than fast twitch fibres. When slow twitch fibres use glycogen as a fuel very little lactate is produced.

Factors affecting the rate of lactate accumulation Rate of blood lactate removal If lactate production increases then lactate will start to accumulate in the blood until OBLA is reached. Training/Fitness Muscle adaptations occur as a result of training. Increased numbers of mitochondria, levels of myoglobin and increased capillary density will improve the capacity for aerobic respiration.

Lactate producing capacity – Sprint/Power Elite sprinters and power athletes are able to cope with higher levels of lactate in the body. This buffering is a process that aids the removal of lactic acid and maintains acidity levels in the blood and muscles. This ability to tolerate higher levels of lactate enable performers to work at higher intensities for longer.

Factors affecting VO 2 max/Aerobic Power An athlete with a high aerobic capacity will be able to utilise a large volume of oxygen. This will increase the intensity with which they can work at before OBLA is reached and fatigue sets in. Think. Pair. Share – What factors will affect a performers VO 2 max reading?

Factors affecting VO 2 max/Aerobic Power Aerobic exercise increases VO 2 max due to the following physiological changes that take place: • Increased maximum cardiac output • Increased stroke volume/cardiac hypertrophy • Greater heart rate range • Increased blood volume and red blood cells count • Increased stores of glycogen and triglycerides • Increased myoglobin (content of muscle) • Increased capillarisation (of muscle) • Increased number and size of mitochondria • Increased concentrations of oxidative enzymes

Factors affecting VO 2 max/Aerobic Power There also a number of general factors that will affect an individual’s VO 2 max reading. • Genetics – inherited factors will limited capacity. • Training – VO 2 max can be improved by up to 20% with the right training. • Age – Older performers will experience a decline in VO 2 max

Factors affecting VO 2 max/Aerobic Power • Gender – Men tend to have 20% higher VO 2 max readings than women. • Body composition – Higher body fat will affect VO 2 max negatively. • Lifestyle – Smoking and poor lifestyle choices all reduce VO 2 max readings.

Measurements of energy expenditure Measuring energy expenditure is an indication of the intensity of exercise and can be used to gauge fitness levels. This method of measurement will also highlight dietary requirements for recovery. Indirect Calorimetry This method measures energy expenditure through gas exchange. Production of CO 2 and/or the rate of O 2 consumption highlights the substrate (fat or carbohydrate) being used.

Measurements of energy expenditure Lactate Sampling Blood lactate measurements are taken using a small blood sample which is analysed to determine exercise intensity, monitor training and predict performance. The higher the pace at which the lactate threshold occurs, the fitter the athlete is considered to be.

Measurements of energy expenditure Lactate sampling allows the performer to select relevant training zones - expressed in terms of heart rate (beats per minute) or power (watts) - in order to get the desired training effect. Regular lactate testing provides a comparison from which the coach and performer can see whether improvement has occurred.

Measurements of energy expenditure VO 2 max tests have been developed to estimate a performer's aerobic capacity. The multistage fitness test The athlete performs a 20 m progressive shuttle run in time with a bleep, to the point of exhaustion. The level reached depends on the number of shuttle runs completed and VO 2 max is ascertained from a standard results table. Think. Pair. Share – Why is the multi-stage fitness test used so widely among many different athletes of all abilities?

VO 2 max tests Average multi-stage fitness test normative tables. Age Excellent Above Average Below Average Poor 14 - 16 L 12 S 7 L 11 S 2 L 8 S 9 L 7 S 1 <L 6 S 6 17 - 20 L 12 S 12 L 11 S 6 L 9 S 2 L 7 S 6 <L 7 S 3 21 - 30 L 12 S 12 L 11 S 7 L 9 S 3 L 7 S 8 <L 7 S 5 31 - 40 L 11 S 7 L 10 S 4 L 6 S 10 L 6 S 7 <L 6 S 4 41 - 50 L 10 S 4 L 9 S 4 L 6 S 9 L 5 S 9 <L 5 Age Excellent Above Average Below Average Poor 14 - 16 L 10 S 9 L 9 S 1 L 6 S 7 L 5 S 1 <L 4 S 7 17 - 20 L 10 S 11 L 9 S 3 L 6 S 8 L 5 S 2 <L 4 S 9 21 - 30 L 10 S 8 L 9 S 2 L 6 S 6 L 5 S 1 <L 4 S 9 31 - 40 L 10 S 4 L 8 S 7 L 6 S 3 L 4 S 6 <L 4 S 5 41 - 50 L 9 S 9 L 7 S 2 L 5 S 7 L 4 S 2 <L 4 S 1

VO 2 max tests The Harvard step test involves the athlete stepping up and down rhythmically on a bench for 5 minutes. The recovery heart rate is then measured and used to predict VO 2 max. The Cooper 12 -minute run This requires the athlete to run as far as they can in 12 minutes and the distance covered is recorded and compared to a standardised table. In this test the performer runs to exhaustion.

Respiratory Exchange Ratio (RER) Energy sources such as carbohydrates, fats and proteins can all be oxidised to produce energy. RER is calculated = Carbon dioxide expired per min (VCO 2) Oxygen consumed per min (VO 2) RER Ratios: • Value of 0. 7 = predominant fuel source is fat • Value 0. 8 -0. 9 = Fuel source is a mix of fats and carbohydrates. • Value of 1. 0 = predominant fuel source is carbohydrate.

Impact of training methods on energy systems Altitude training: The percentage of oxygen (O 2) in the air is the same at sea level and at altitude. However, the partial pressure of oxygen decreases as altitude increases. This causes a reduction in the diffusion gradient between the air and the lungs and between the alveoli and the blood. As a result, haemoglobin is not fully saturated at altitude, which results in a lower oxygencarrying capacity of the blood.

Impact of training methods on energy systems As less oxygen is delivered to working muscles there is an earlier onset of fatigue. This results in a decrease in aerobic performance. The body's response to the reduced levels of oxygen provides a number of advantages. Disadvantages include altitude sickness, expensive and the effects can be lost quickly upon returning to sea level.

Impact of training methods on energy systems High Intensity Interval Training (HIIT) This type of training involves repeated bouts of high intensity effort followed by varied recovery times. These short, intense workouts will improve aerobic capacity. HITT training therefore improves fat burning potential and glucose metabolism.

Impact of training methods on energy systems A typical HIIT session will include: • Exercise intensity – 80 -95% of max HR • 1: 1 work to rest ratio i. e. 30 seconds mountain climbers (work) followed by light jog for 30 seconds (recovery) HIIT can be modified for different athletes of varying abilities. Cyclists and swimmers use it as a cross training method to add variance to a programme.

Impact of training methods on energy systems Plyometrics Training is one method of strength training that can be used to improve power or elastic strength. e. g. long jumpers, 100 m sprinters or basketball players Plyometrics works on the concept that muscles can generate more force if they have previously been stretched. The muscle performs an eccentric contraction (lengthens under tension) followed immediately by a concentric contraction as the performer jumps up.

Impact of training methods on energy systems This stimulates adaptations within the neuromuscular system and results in a more powerful concentric contraction of the muscle group being worked. Strength gains through plyometrics usually become apparent following a training period of about 8 -10 weeks. (Muscle hypertrophy)

Impact of training methods on energy systems Speed, agility, quickness (SAQ) This method of training combination three important fitness components and is particularly used by games players. As SAQ training involves activities performed at high intensities, energy is provided anaerobically. Drills include ladder work, mini hurdles and zig zag runs.

Apply it! What has stuck with you? Describe the ATP-PC system? What is meant by the energy continuum? Energy systems Explain the meaning of OBLA What measurements can be taken to assess energy expenditure of an athlete?

Practice it! Exam questions 1. Identify two functions of the fast component of Excess Post. Exercise Oxygen Consumption (EPOC) [1] A B C D Break down lactic acid and normalise body temperature Resaturate myoglobin with oxygen and normalise body temperature Restore phosphocreatine (PC) and break down lactic acid Restore phosphocreatine (PC) and resaturate myoglobin with oxygen 2. Explain how the characteristics of fast twitch glycolytic muscle fibres (type IIx) are suited to producing ATP anaerobically during powerful contractions. [2]

Practice it! Exam questions 3. Table 2 shows the times of an elite athlete for a 100 m, 400 m and 3000 m race. Figure 2 shows the relative contribution of the energy systems on the energy continuum. [15] Using Figure 2, analyse and evaluate the contribution of each energy system for each event identified in Table 2.

Practice it! Marks Scheme: 1. D 2. High PC stores – increased energy source for ATP production via the ATP-PC system (1). • High glycogen stores – increased energy source for ATP production via the lactate anaerobic system (1). • High myosin ATPase activity – increased enzyme activity for ATP production within the ATP-PC system (1). • High glycolytic enzyme activity – increased enzyme activity or ATP production within the lactate anaerobic system (1).

Practice it! Marks Scheme: 3. AO 1 – Knowledge Identified and described the energy systems, eg ATP-PC system involves the breakdown of PC to form ATP. The aerobic system uses oxygen to release energy. The aerobic system has a higher ATP yield than the other systems. (No reference to times from table is required). AO 2 – Application Identified and explained the contribution of each system in the three events, eg in the 100 m event, the athlete will predominantly use the ATP PC system to create ATP. There is also some contribution from the lactate anaerobic system. This is because the ATP-PC system can create ATP for 8– 10 seconds and the race only takes 10. 49 seconds to complete. This involves the breakdown of glucose anaerobically to form pyruvic acid and then lactic acid which is also known as anaerobic glycolysis. AO 3 – Analysis/Evaluation Linked the contribution of each energy system to the demands of the event, eg 100 m uses ATPPC system which is an anaerobic system to create ATP as it is a sprint event and the performer runs as fast as they can and so intensity is maximal. When ATP is made through the breakdown of PC in the ATP-PC system, ATP is produced very quickly explaining, the 100% capacity in Figure 2. Credit other relevant analysis and evaluation points in relation to the contribution of each energy system for each event identified in the data.