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CHAPTER 2 CHAPTER 2 Energy systems The energy for muscular contractions comes from adenosine triphosphate (ATP), which is found in several sources including our food and drink. It may be released from carbohydrates, fats or proteins, depending on the body’s state of activity or health. The body produces adenosine triphosphate via three energy pathways. Each is the main provider under specific exercise conditions, but all contribute to energy across all degrees of activity. Each energy system has strengths and weaknesses when compared with the others, and specific sporting performances exemplify each system’s majority contribution to the production of adenosine triphosphate. This chapter explores the three basic chemical pathways in the production of adenosine triphosphate: the phosphate energy system, the anaerobic glycolysis system and the aerobic system, along with their relative characteristics and interplay. The lactate threshold is a major concept in energysystem theory. To understand the relationship between energy systems and physical activity, it is useful to have a knowledge of microscopic muscular activity and how it utilises ATP; however, note that the microscopic structure of muscles is no longer assessable under the 2006–09 VCAA Physical Education study design. 58 1_61_02472_LIU2ch2.indd 58 2/12/05 9:17:33 AM Assessment tasks Task Topics Page Written reports Individual diet and energy (activity 2) The citric acid cycle and the electron transport chain (activity 5) 61 71 Case study analysis Elite performers’ diet and energy (activity 1) 61 74 Laboratory reports The phosphate energy system (activity 3) The anaerobic glycolysis system (activity 4) The aerobic glycolysis system (activity 7) 67 69 76 Structured questions The onset of blood lactate accumulation (activity 8) 77 After completing this chapter, students should be able to: CHAPTER 2 Data analysis exercise Phosphate energy efforts linked to the other energy systems (activity 6) • Identify the characteristics of the three and the effect that the onset of blood lactate energy systems and the fuels required for accumulation (OBLA) has on effort physical activity. • Analyse why fatigue occurs and how this is • Describe the ways in which ATP is produced linked to fuel depletion and metabolic under different activity conditions and the by-products processes of muscular contraction • Outline the central role that the lactate • Explain the interplay between the three energy threshold has in activity intensity and duration. systems under varying activity intensities 59 1_61_02472_LIU2ch2.indd 59 2/12/05 9:17:33 AM Why energy? Your body needs energy for basic body functions and activity during your whole life — energy for breathing, sleeping, digesting, sitting in a chair, sprinting for a bus, and everything else you do day and night. The interaction between muscles and bones keeps the body upright and under control. To allow this teamwork between the muscular and skeletal systems (see chapter 5, Live It Up 1 second edition), the body needs energy sources that permit muscles to work — for example, the effort needed by the abdominal and back muscles to enable good sitting posture, or by the muscles of the abdominals, back, legs, torso and arms during a softball game. Adenosine triphosphate The chemical compound adenosine triphosphate (ATP) provides the energy that allows muscular effort. ATP is the energy source for all muscular effort, whether for a small subconscious movement such as the blinking of an eye, or a planned repetitive effort in weight training (see chapters 7 and 9). Sources of ATP ATP is an end-product of your diet. All the food, processed drinks and water that you consume contain nutrients that your body requires for: • healthy growth • repair of body ‘wear and tear’ from everyday activities • energy for all bodily functions. The components of a healthy diet are: • carbohydrate • fat • protein • vitamins and minerals • water. ATP can be created from carbohydrate, fat and protein. Chapters 3 and 11 more fully explore the processes by which the body produces energy from food. Carbohydrate When carbohydrate is digested, it is broken down to glucose for blood transportation and then stored as glycogen in the muscles and liver. Glycogen can provide the energy for ATP production under both anaerobic (no oxygen required) and aerobic (oxygen required) conditions. Fat Fat provides the major source of energy for long-term physical activity. During a long team game or a marathon, fats (as either triglycerides or free fatty acids) usually contribute to ATP production to meet sub-maximal energy demands. Under special conditions, the athlete may be able to use fat earlier in the activity to ‘spare’ the carbohydrate stores and therefore enable longer high-level effort (see chapter 11). During rest conditions, fat produces the majority of the required ATP. Protein Protein only minimally contributes to ATP production. In extreme circumstances (such as starvation or ultra triathlon/marathon events) when the body has severely depleted its supplies of carbohydrate and fat, proteins can become a viable source of ATP. LIVE IT UP 2 60 1_61_02472_LIU2ch2.indd 60 2/12/05 9:17:34 AM Table 2.1 Assesment tasks The body’s storage of food fuel Food fuel Stored as Site Carbohydrate Glucose Glycogen Adipose tissue (including storage of excess carbohydrate) Blood Muscle and liver Around the body Fat Free fatty acids Triglycerides Adipose tissue Blood Muscle Around the body Protein Muscle Amino acids Skeletal muscle Body fluids Activity 1 Key knowledge • Fuels required for physical activity and the conversion of food to energy Case study analysis Elite performers’ diet and energy Choose one of the research tasks below and write a brief account of your findings. In your account, try to address these questions: How much emphasis is given to carbohydrate, fat and protein? Why? a Use the Internet to research the diet of one or more top Australian athletes. (Alternatively, go to www.jaconline.com.au/liveitup/book2 and click on the Australian Sports Commission link.) or b Interview a local high-level sportsperson, asking them about their diet. Activity 2 Key knowledge • Fuels required for physical activity and the conversion of food to energy Written report Individual diet and energy Record your total diet for three days. Assess the percentages of carbohydrate, fat and protein. Using your own dietary knowledge as a guide, how could you improve your diet to meet your energy needs? Write a brief report on your findings. Energy from ATP Adenosine (three phosphate molecules attached) ATP Food Energy ATP is stored in limited quantities within muscle, so each muscle fibre must be able to create its own supplies from the food fuels. Figure 2.1 illustrates how the metabolism of food creates ATP, which then provides energy for muscular exertion. Energy Muscle activity ADP + P Adenosine (two phosphate molecules attached) Figure 2.1: + Free phosphate CHAPTER 2 Energy for muscular activity — from food to ATP to muscles ENERGY SYSTEMS 61 1_61_02472_LIU2ch2.indd 61 2/12/05 9:17:37 AM ATP is an adenosine molecule with three phosphate molecules attached. When muscular activity is needed, one of the phosphate molecules breaks off, releasing energy and creating adenosine diphosphate (ADP). This process is reversible: figure 2.2 shows how ADP can become ATP. This occurs continually during the activity as long as sufficient energy substrates are available. Food + muscle substrates Figure 2.2: The conversion of ADP to ATP ADP + Free phosphate + Energy ATP Depending on the type of physical activity (see chapter 8, Live It Up 1 second edition), energy substrates include phosphocreatine, glucose, glycogen, lactic acid, fat, protein and oxygen. A muscle fibre stores only a small amount of ATP, so the force and duration of a muscular effort is only as effective as the ATP replenishment process. During and after physical exertion, the body uses several methods of recovery to rebuild used supplies of ATP and food fuels. Chapter 4 investigates this recovery process. Energy for rest and activity The body can create energy (ATP) under two main conditions: 1. rest conditions, where there is sufficient oxygen available for the body to continue to function at a resting level 2. active conditions, where physical exertion means there is insufficient oxygen available for the body to continue to function at a particular level without a marked increase in oxygen intake either during or after the effort. These conditions occur during anaerobic activity and aerobic activity. ATP production during rest conditions Rest is when the body is not under physical stress and when breathing and heart rates are at resting levels. The body has an abundant oxygen supply, so it produces approximately two-thirds of the ATP from fat stores within the muscle and elsewhere in the body. Fat is a much richer energy source than carbohydrate. To release this energy, the body must use much more oxygen than it would in activating the supplies of ATP from glucose. When at rest, you have an abundant supply of oxygen which is above the body’s metabolic demands. The other third of ATP needed under rest conditions comes from carbohydrate in blood glucose and glycogen stores within both the muscle and liver. As with fat, glycogen is broken down in the mitochondria (structures within the muscle cell, referred to as the ‘powerhouses’ of the cell; see figure 2.12, page 71). The end products of aerobic metabolism are carbon dioxide, water and heat. No by-products limit body activity; only food fuels and the rate of aerobic metabolism limit ongoing aerobic ATP production. ATP production during activity ‘Activity’ in physical education is a wide-ranging term that covers any physical state more exertive than rest. The level of activity is determined by factors such as: • how long the activity continues (activity duration) • how hard the body works during the activity (activity intensity) • the level of the individual’s aerobic fitness LIVE IT UP 2 62 1_61_02472_LIU2ch2.indd 62 2/12/05 9:17:38 AM • the level of recovery achievable between activity efforts. When the body starts physical activity, it immediately demands an increased oxygen supply to the working muscles. The respiratory and circulatory systems (see chapter 6, Live It Up 2) are unable to meet this immediate demand, so the body uses two energy pathways to create ATP anaerobically (that is, without oxygen). These anaerobic pathways produce ATP quickly and powerfully, but they have three disadvantages: • they produce relatively small amounts of ATP • they operate for only a short period • they result in fatiguing by-products. If the physical activity is at a reasonably sub-maximal level, then the body is able to produce the required ATP aerobically because the body’s ability to use oxygen can meet the muscles’ demands for extra oxygen for greater ATP production. This aerobic pathway has opposite qualities to those of the two anaerobic systems: • it can produce ATP for sub-maximal efforts for long periods of time • it cannot quickly produce energy for high-intensity efforts • it has no toxic by-products. The body produces ATP under these varying levels of physical activity via three energy pathways: the phosphate energy system, the anaerobic glycolysis system and the aerobic system. Note: The following information on the microscopic structure of skeletal muscle, pages 63–5, is not assessable under the 2006–09 VCAA Physical Education study design. However, it has been included here as it provides a useful understanding of the end product of each of the three energy systems — muscular contractions. Tendon Belly Microscopic structure of skeletal muscle As the end product of each of the three energy systems, adenosine triphosphate directly initiates all muscular contractions. A knowledge of the microscopic structure of skeletal muscle is needed to appreciate the role of ATP. A more thorough understanding of muscle groups and action is found in chapter 5. Skeletal muscle is covered with a layer of connective tissue called the epimysium. The epimysium thickens as it reaches the ends of the muscle to form tendons that usually attach to bone. Skeletal muscle consists of thousands of muscle fibres that run the length of the muscle and are arranged in bundles called fasiculi. (A single bundle is called a fasiculus.) Each individual muscle fibre is surrounded by connective tissue called the endomysium which binds the fibres together to form the bundles. The fasiculi are surrounded by a layer of connective tissue called the perimysium which helps bind the fasiculi together. Muscle fibre Endomysium: connective tissue that binds fibres together to form bundles Epimysium: layer of connective tissue that thickens to form tendons at ends of muscle Tendon Perimysium: connective tissue that surrounds the fasiculi Figure 2.3: Fasiculus: bundle of muscle fibres The muscle belly in cross-section CHAPTER 2 ENERGY SYSTEMS 63 1_61_02472_LIU2ch2.indd 63 2/12/05 9:17:39 AM The muscle fibre Figure 2.4: Scanning electron micrograph of an insect flight muscle. You can see three large muscle fibres, along with the individual myofibrils making up the fibres. Each muscle fibre is surrounded by a cell membrane called the sarcolemma. Underlying the sarcolemma is a gel-like fluid called sarcoplasm. This fluid contains: • mitochondria, which are the site of aerobic energy production • myoglobin, which carries oxygen to the mitochondria • fat, carbohydrate and protein (energy nutrients) • adenosine triphosphate (an immediate energy source) • enzymes, which are chemicals that speed up energy production • actin and myosin myofilaments (contractile proteins). Each muscle fibre is made up of long strands called myofibrils. Each myofibril consists of many individual units (called sarcomeres) that are responsible for contracting the muscle. Sarcomeres A sarcomere is a contractile unit, and each one is designated by a line at either end called a Z line. Each sarcomere consists of two protein myofilaments called actin and myosin. Actin is a thin filament that attaches to the Z line. Myosin is a thick filament situated between each of the actin filaments. Figure 2.5 illustrates the several bands and zones that help define the sarcomere: • the I band, where only actin is found • the A band, where both actin and myosin are found. It equates with the length of the myosin filaments. • The H zone, where only myosin is found. It is the gap between the ends of the actin. I band A band Myofibril Z line Z line Muscle fibre Sarcomere Myofibril Z line H zone Z line Cross bridge Figure 2.5: Arrangement of sarcomeres within the muscle fibre Thick (myosin) filament Thin (actin) filament LIVE IT UP 2 64 1_61_02472_LIU2ch2.indd 64 2/12/05 9:17:52 AM Cross bridges The myosin filaments have cross bridges (oar-like structures) that are attracted to the actin filaments (figure 2.5). At rest, there is little contact between the actin and the myosin; however, when the sarcomere contracts, the cross bridges attach to the actin filaments and pull them into the centre of the sarcomere in a ‘rowing’ action. The cross bridges continue to detach and reattach themselves from the actin filaments, shortening the sarcomere. Every sarcomere along the muscle fibre shortens, leading the whole muscle to contract. The muscle will relax when the actin and myosin filaments lose contact with each other — that is, when the cross bridges detach from the actin. A band Figure 2.6: Structural rearrangement of actin and myosin filaments at rest (at 1) and during contraction (2–4) H zone I band Z line 1 2 3 4 Source: S. Powers and E. Howley, 2004, Theory and Application to Fitness and Performance, 5th edn, © McGraw-Hill Companies, Inc. CHAPTER 2 ENERGY SYSTEMS 65 1_61_02472_LIU2ch2.indd 65 2/12/05 9:17:59 AM Three energy systems All three energy pathways operate at any one time, but the contribution of each varies depending on the intensity of the activity. Figure 2.7 illustrates the overlapping nature of the three energy systems which underpins their ‘interplay’. Note that the identified percentage contribution of each energy system to exertions of different durations has changed with sports physiology research over the years. A graphic interpretation of the three energy systems and their periods of importance 100 Figure 2.7: 75 Aerobic energy 50 25 0 Anaerobic glycolysis Phosphate energy 0 10 30 60 90 120 180 240 300 360 Phosphate energy system The phosphate energy system has some alternative names (usually shorthand versions): the phosphocreatine (PC) system, the ATP–PC system, the phosphagen system or the PC (or CP) system. This system provides the bulk of ATP during powerful or explosive efforts. Such efforts may be a one-off, such as a court-length pass in basketball or a take-off in the high jump, or ongoing, such as a sprint to position in netball or football. The phosphate energy system is closely linked with several fitness components (see chapter 5): • muscular strength • muscular power • anaerobic power • speed • agility • reaction time. Following about 10 seconds of maximal effort, the phosphate system is largely depleted and the body needs to significantly reduce the activity’s intensity as the anaerobic glycolysis system begins to become the dominant provider of ATP. The phosphate energy system relies on muscle stores of both ATP and a chemical compound called ‘phosphocreatine’. If the activity requires a maximal effort for 5–10 seconds, such as a 100-metre sprint event, then stores of ATP and phosphocreatine in the working muscles jointly create most of the maximal effort for that activity. From the push off the starting blocks until a few seconds into the sprint, the muscles’ ATP stores provide the energy for the repeated muscular contractions. ATP supplies in the muscles diminish, and the amount of ADP left from the spent ATP grows. At this point in the race, the stores of phosphocreatine create new ATP from the ADP, allowing the performer to complete the sprint. The chemical bond holding the phosphate and the creatine together is quickly broken, releasing energy that is used to reconstitute ATP from ADP (figure 2.8). LIVE IT UP 2 66 1_61_02472_LIU2ch2.indd 66 2/12/05 9:17:59 AM Figure 2.8: Creatine The release of energy from phosphocreatine for ATP production is quick and efficient, but short-lived. ATP Phosphate Energy Energy Creatine ADP + Free phosphate From just a few seconds into an all-out phosphate effort, the anaerobic glycolysis system begins to work (Journal of Science and Medicine in Sport, vol. 6, Issue 2, June 2003). This results in increasing levels of lactate and hydrogen ions within the working muscles. However, these levels do not inhibit muscular action at this stage. After about 10 seconds of effort, the muscles’ stores of phosphocreatine are also greatly depleted. Thus, with critically low stores of both ATP and phosphocreatine, the athlete must either slow down or stop. Once this maximal effort is over, the body is able to take in more oxygen via puffing. This extra oxygen is able to create more ATP from ADP, and to reconstitute phosphocreatine from the broken phosphate and creatine molecules remaining after the sprint. Following a 10-second maximal effort, the body can take around 3–5 minutes to fully restore the ATP and phosphocreatine supplies to preexercise levels within the working muscles. Latest research suggests 50 per cent phosphocreatine replenishment can happen in the 30 seconds of rest recovery (Journal of Science and Medicine in Sport vol. 6, Issue 2, June 2003). If the effort was less than 10 seconds, then the recovery time to pre-exercise levels is relatively faster at 5 minutes. Chapter 4 contains more detail on this recovery process. Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity Key skills • Describe the interplay of the energy systems, using correct terminology. • Analyse the relationship between energy systems and physical activity. • Perform, observe, analyse and report on laboratory exercises designed to explore the relationship between energy systems during physical activities. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Activity 3 Laboratory report The phosphate energy system As a class, choose three test subjects to thoroughly warm up and then attempt a series of 50-metre sprints. Allow gradually reduced recovery periods after each sprint of: • 5 minutes • 3 minutes • 1 minute • 10 seconds. Each subject takes their heart rate for 10 seconds after each sprint. If you are not a test subject, help organise and record the runs. a Graph and discuss the results. b Write a report in which you explain the peak time for the phosphate energy system, its required recovery period and how the laboratory demonstrated this theory. CHAPTER 2 ENERGY SYSTEMS 67 1_61_02472_LIU2ch2.indd 67 2/12/05 9:18:02 AM Anaerobic glycolysis system Figure 2.9: Jana Pittman winning another 400-metre hurdles race. Her effort produces a large amount of lactate and hydrogen ions. The anaerobic glycolysis system also has some alternative names: the lactic acid system or the lactacid system. This system mainly provides the bulk of ATP production during high-intensity, submaximal efforts. It may also become the dominant producer of ATP during repeated phosphate efforts which have insufficient recovery time to allow full phosphocreatine replenishment. Further, when a performer has gone beyond their maximum oxygen uptake level (their VO² max — see page 75) during an endurance event, the anaerobic glycolysis and aerobic systems share the task of creating ATP for the few minutes it will take the performer to stop from exhaustion. In this situation approaching exhaustion, a performer is working at greater than 100 per cent of their maximum oxygen capacity. This is due to the anaerobic input into the effort. Chapters 5 and 7 will further investigate this situation. The anaerobic glycolysis system operates as the dominant supplier of ATP in the period from around 10 seconds of maximal effort to around 60 seconds of high-intensity sub-maximal effort. Most recent studies suggest that the overlap period — when the body switches from using the anaerobic glycolysis system as the dominant ATP producer to using the aerobic system — could start as early as 30 seconds into high-level, sub-maximal activity. The anaerobic glycolysis system is closely linked with several fitness components (see chapter 5): • anaerobic power • local muscular endurance • speed • muscular power. It is classically exemplified in the 400-metre run in secondary school athletics, but it is also highly relevant in a team game when the performer is required to undertake repeated sprints that do not provide sufficient recovery time for the phosphate system. Most players in team games can relate to a situation of having insufficient energy to allow continued top effort, and thus needing a time-out or a rest on the substitution bench. Chapter 4 more fully explains the steps leading to this fatigue. During the 400-metre athletic event, the production of ATP relies on all three energy systems but predominantly on anaerobic glycolysis. When the athlete pushes off the starting blocks, the phosphate energy system allows for an explosive start to the race. However, this system quickly loses its primary role in ATP production as anaerobic glycolysis begins to dominate. The glycogen stores within the muscle are worked on (without the need for oxygen in the muscles) to create ATP, allowing the muscles to continue to propel the body down the back straight of the 400-metre track. The working muscles need ATP at a faster rate than can be adequately provided by the complete breakdown of glucose through aerobic metabolism. Therefore, the pyruvic acid created by anaerobic glycolysis cannot be processed by oxygen, and it is converted to lactic acid. Hydrogen ions are also released (figure 2.10 opposite). When lactate and hydrogen ions accumulate in the muscles during high-intensity exercise, muscular contractions are inhibited. The body can tolerate increasing levels of lactate and hydrogen ions production only until their accumulation rate is greater than the body’s ability to remove them. At this stage there is an exponential increase in lactate and hydrogen ions levels within the muscle. This is called the lactate threshold: once the athlete passes this threshold, they must reduce or stop their muscular effort. LIVE IT UP 2 68 1_61_02472_LIU2ch2.indd 68 2/12/05 9:18:03 AM Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity Key skills • Describe the interplay of the energy systems, using correct terminology. • Analyse the relationship between energy systems and physical activity. • Perform, observe, analyse and report on laboratory exercises designed to explore the relationship between energy systems during physical activities. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Activity 4 Laboratory report The anaerobic glycolysis system As a class, thoroughly warm up and then run a 400-metre race. a Stop when you reach the point when you think your lactate levels are beginning to affect your running. b In groups of four to six students, write up your responses and present them to the class. The energy used by a busy rover during an Australian Football game or a wing attack during a netball game also relies on anaerobic glycolysis for a large proportion of ATP production during the game. The recovery time for the phosphate energy system after an exhaustive 10-second maximal effort is about 3–5 minutes. Therefore, after a 5-second maximal effort, the recovery time is roughly equivalent to 1–2 minutes; after a 1-second effort, it may be about 10 seconds. Glycogen Glucose ATP Energy for muscle Energy ADP + Free phosphate Figure 2.10 The process of anaerobic glycolysis is more complex than the phosphate energy system, with around eleven steps compared with two. Pyruvic acid no oxygen Lactic acid + hydrogen ions CHAPTER 2 ENERGY SYSTEMS 69 1_61_02472_LIU2ch2.indd 69 2/12/05 9:18:05 AM During 20 minutes of a football or netball game, an involved player may carry out over 100 phosphate efforts (see chapter 5). Even if adequate oxygen-rich recovery conditions are available between each effort, there is still only around 10 seconds for recovery each time. Therefore, the phosphate energy system usually becomes severely depleted in sources of ATP production, and the next quickly available system (anaerobic glycolysis) takes over as the dominant ATP supplier. During a 400-metre run, lactic acid accumulating in the leg muscles affects the runner in the home straight but generally can be endured until the end of the race. In a team game, however, too much lactic acid build-up will impair subsequent performance and cannot be ignored. Aerobic energy system The aerobic energy system includes the aerobic glycolysis system. It is relevant to all of the fitness components because it provides either the basis for recovery between strength and power efforts, or the bulk of energy for sub-maximal efforts. Aerobic glycolysis, as with all the energy systems, contributes to ATP production under all conditions. However, it contributes the majority of ATP during continuous sub-maximal activities which go beyond 1 minute. This system can create thirty-eight molecules of ATP from one molecule of glucose, whereas anaerobic glycolysis creates only two. This extra amount is possible because the abundance of oxygen allows a more complete breakdown of glucose than occurs in anaerobic glycolysis. Pyruvic acid, rather than becoming lactic acid, is further broken down in the citric acid cycle and the electron transport chain within the mitochondria (figure 2.12). Figure 2.11: Glycogen The process of aerobic glycolysis is more complex than the other two systems, providing both advantages and disadvantages in ATP production. Glucose ATP Energy for muscle Energy ADP + Free phosphate Pyruvic acid (+ oxygen) Fats (and oxygen) + Protein (emergency ATP source) Citric acid cycle ATP for muscle Hydrogen ions Electron transport chain ATP for muscle LIVE IT UP 2 70 1_61_02472_LIU2ch2.indd 70 2/12/05 9:18:06 AM Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity • Fuels required for physical activity and the conversion of food to energy Key skills • Analyse the relationship between energy systems and physical activity. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Activity 5 Written report The citric acid cycle and the electron transport chain Find some reliable physiology websites on the Internet. The following search words should be of help: • aerobic energy • ATP • citric acid cycle • electron transport chain • fat oxidation • muscle energy. Write a report on either: a fat oxidation within the citric acid cycle or b hydrogen ions, their role in fatigue and their oxidation in the citric acid cycle and electron transport chain. With the rich oxygen supplies in the aerobic system, fat is able to become a significant contributor to ATP production. One molecule of fat can release over 100 molecules of ATP, but at a much slower rate than the release from glucose. Fat requires a complex series of reactions that depend on oxygen within the citric acid cycle in the mitochondria. (Protein is similarly metabolised for ATP production, but only under the extreme conditions mentioned earlier.) The body’s supply of fat exceeds even the physical requirements of a highly trained athlete, so the aerobic system can theoretically operate for an unlimited work period. What prevents us happily jogging, cycling or swimming forever are a few other factors concerning our bodies during physical activity: • dehydration • hypothermia or hyperthermia • muscle damadge • joint damage • specific energy-system enzyme inactivation • neural fatigue • mental fatigue or boredom • time pressures — other things to do! Mitochondrion Figure 2.12: The mitochondrion carries out aerobic glycolysis, involving glycogen breakdown that produces water and carbon dioxide as by-products. Also, pyruvic acid is now further broken down in the citric acid cycle, and both fat and protein can be metabolised. Glycogen Glucose Fat ATP Pyruvic acid Protein Citric acid cycle Carbon dioxide Hydrogen Oxygen ATP Electron transport chain CHAPTER 2 Water ENERGY SYSTEMS 71 1_61_02472_LIU2ch2.indd 71 2/12/05 9:18:09 AM Characteristics of the aerobic system • Much slower energy production than that of the anaerobic systems • Lag of 2–5 minutes until the individual reaches a ‘steady state’ (where the respiratory system’s increased oxygen intake meets the activity’s oxygen demands). The aerobic production of ATP plateaus at the required exercise intensity level (figure 2.13). • Dominant contributor to ATP production only at sub-maximal exercise conditions • Limited contribution to ATP production once the lactate threshold is passed, given the increasing debilitating effects of lactate and hydrogen ions. Figure 2.13: When you begin to exercise, the more quickly responding anaerobic systems contribute the bulk of ATP production until the aerobic system reaches its steady state 2–5 minutes later. Total ATP production ATP production Anaerobic production Aerobic systemʼs production Onset of exercise 0 3 5 Time (minutes) Table 2.2 Summary of the three energy systems Characteristic Phosphate energy Anaerobic glycolysis Aerobic glycolysis 1. Energy source for ATP production Phosphocreatine Carbohydrate Glycogen Carbohydrate Fat Protein 2. Number of ATP molecules made from one molecule of energy source Phosphocreatine: less than one Glucose: approximately two Glucose: thirty-eight Fat: more than 100 3. Maximal rate of ATP production (molecules/minute) 3.6 1.6 1.0 4. Duration of peak energy production 5–10 seconds 30–45 seconds 3–7 minutes (time above the lactate threshold; see pages 75–6) 5. Percentage contribution at 25 per cent of VO² max Less than 5 per cent Approximately 15 per cent Approximately 80 per cent LIVE IT UP 2 72 1_61_02472_LIU2ch2.indd 72 2/12/05 9:18:10 AM Table 2.2 (continued) Summary of the three energy systems Characteristic Phosphate energy Anaerobic glycolysis Aerobic glycolysis 6. Percentage contribution at 65 per cent of VO² max Approximately 5 per cent Approximately 45 per cent Approximately 45 per cent 7. Percentage contribution at maximal sprint 55 per cent 40 per cent 5 per cent 8. Recovery time until repeat effort Phosphocreatine replenishment: 3-5 minutes • 50 per cent recovery in first 30 seconds • Rest recovery best Depends on time above lactate threshold. Removal of lactic acid to rest levels: • with active recovery: – 50 per cent removal: 15 minutes – 95 per cent removal: 30 minutes • with passive recovery: – 50 per cent removal: 30 minutes – 95 per cent removal: 60 minutes Restoration of body glycogen stores: • after competition of more than 1 hour: 24–48 hours • after hard interval training: 6–24 hours 9. Limiting factor when operating maximally Depletion of phosphocreatine Lactate and hydrogen-ion accumulation Lactate and hydrogenion accumulation • Glucose and glycogen stores • Overheating (hypothermia) 10. Intensity and duration of activity where the system is dominant ATP provider Maximal intensity (>95 per cent) and duration of 1–10 seconds High, sub-maximal intensity (85–95 per cent) and duration of 10–30 seconds Sub-maximal intensity (85 per cent) and duration of >30 seconds 11. Specific sporting examples • Any athletic field event • Elite 100 m athletic sprint • Golf drive • Gymnastic vault • Volleyball spike • High mark and long kick in AFL • Tennis serve • Water polo centre forward–centre back contest • 200–400 m in athletics • 50 m swim • Consecutive basketball fast breaks • High intensity 15–20 second squash rally • Repeated leads by AFL full forward • Elite netball centre in close game • Quadriceps in downhill skiing • Water polo consecutive fast breaks and defends • • • • • • • • Marathon Cross-country skiing Triathlon AFL mid field Hockey wing All elite team players Rowing 2000 m race Water polo game 12. Everyday activity examples • Running up one flight of steps • Carrying heavy shopping from car to house • Sprinting for train • Running up four flights of stairs • Running 200 m to catch bus • Chopping wood • Moving heavy furniture • • • • • • Shopping Going to the cinema Gardening Dancing Ironing Studying CHAPTER 2 ENERGY SYSTEMS 73 1_61_02472_LIU2ch2.indd 73 2/12/05 9:18:10 AM Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity • Fuels required for physical activity and the conversion of food to energy • Muscular fatigue mechanisms, specifically fuel depletion, metabolic by-products, and dehydration Activity 6 Data analysis exercise Phosphate energy efforts linked to the other energy systems Watch a replay of any high-level team game (either a professional recording or one you have filmed yourself). Assign groups to record all phosphate efforts by the players. a Assess the average length of each effort and the average recovery time between each. b Determine the relative importance of each of the three energy systems to the game. Key skills • Describe the interplay of the energy systems, using correct terminology. • Analyse the relationship between energy systems and physical activity. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. ATP production — different exertion conditions The length and intensity of physical exertion determine which of the energy systems is the dominant contributor to ATP production (figure 2.14). As the activity time increases, the influence of the aerobic system on ATP production also increases. However, the relative contribution of each of the three energy systems varies according to the intensity and duration of the activity. Figure 2.14: The average energy contributions of different energy systems during high-intensity competition ATP Phosphocreatine 50% Anaerobic glycolytic Aerobic glycolytic 8% 6.3% 50% 50% 65% 44.1% Aerobic lipolytic 92% 30% 50% 49.6% Source: John Hawley & Louise Burke 1998, Peak Performance: Allen & Unwin, St Leonards, p. 47 50% 35% 20% 6 seconds 30 seconds 60 seconds 120 seconds 1 hour 4 hours LIVE IT UP 2 74 1_61_02472_LIU2ch2.indd 74 2/12/05 9:18:12 AM Energy expenditure (cal/kg/min) 300 200 100 0 25 65 85 Exercise intensity Fats (% of maximum Glycogen oxygen uptake) Figure 2.15 The contributions of body fat and carbohydrate stores to activity performed at varying percentages of maximum oxygen uptake ATP production Source: Adapted from The Physician and Sportsmedicine, vol. 26, no. 9, 1998 Anaerobic systems Aerobic system Exercise intensity Figure 2.16: The aerobic and anaerobic contributions to ATP production as exercise intensity increases — the lactate threshold is the point at which the intensity increases such that lactic acid production exceeds lactic acid removal. The contribution of either carbohydrate or fat to ATP production varies according to the activity intensity. This is usually measured against the maximum oxygen uptake (VO² max = the maximum volume of oxygen that the body can use, measured in millilitres per minute per kilogram — see chapters 6 and 8). A low-intensity activity such as walking uses about 25 per cent of maximum oxygen uptake and elicits high levels of fat mobilisation from around the body to generate ATP. This is one reason for prescribing long walking sessions as a valuable exercise for weight control. Walking mobilises only small amounts of carbohydrates, with blood glucose supplies meeting the body’s carbohydrate needs. Figure 2.15 indicates that an activity performed at 65 per cent of maximum oxygen uptake (such as easy jogging) produces significant rates of fat oxidation to create ATP; at an activity level of 85 per cent of maximum oxygen uptake (a level at or above the lactate threshold for non-elite athletes), fat contributions decline and carbohydrate assumes dominance in ATP production. OBLA OBLA is the acronym for the onset of blood lactate accumulation. At rest, everyone has lactic acid in their muscles. This would be measured at very small levels of around 1mmol/L of blood. It is only when exercise begins that the muscular levels of lactic acid (LA) begin to rise. At the same time as these begin to rise, the levels of hydrogen ions (H+) within the muscles also rise. If the exercise or activity is anaerobic in nature, then the levels of both lactate and H+ rise more significantly. At the early stages of anaerobic work, the building muscular concentrations of both lactate and H+ easily flow from the working muscles through the capillary walls into the circulatory system. This flow follows the widely understood maxim that ‘higher concentrations always flow towards lower concentrations.’ In the early stages of anaerobic work, the blood and plasma concentrations of lactate and H+ are lower than within the working muscles. An increase in blood and plasma levels of lactate and H+ is the signal that OBLA has occurred. This is easily measured at elite training venues such as the AIS in Canberra where technological facilities and sports scientists are available to quickly take and measure blood samples from the elite athletes that train with the AIS. When these readings are combined with an athlete’s record of their physiological responses to exertion, training can be tightly geared around both their OBLA and their lactate threshold. Lactate threshold Traditionally called the ‘anaerobic threshold’ (a misleading term), the lactate threshold is the common term used at the elite level of sports physiology. It is the point above which lactic acid begins to rapidly accumulate in the blood, and below which blood levels of lactic acid do not inhibit aerobic effort at the desired level. Beyond the lactate threshold, muscle and blood lactate levels exponentially increase and the athlete has to reduce or stop muscle effort. For ordinary people, the lactate threshold is usually around 4 mmol/L of LA. Trained athletes can increase their tolerance to LA accumulation and are able to continue effective performance or training with much higher lactate and H+ levels in their working muscles and circulatory system. At the AIS, athletes’ LA levels have been measured at above 20 mmol/L while continuing to effectively train or compete anaerobically. CHAPTER 2 ENERGY SYSTEMS 75 1_61_02472_LIU2ch2.indd 75 2/12/05 9:18:13 AM Once the athlete passes the lactate threshold and continues the activity until reaching exhaustion, all energy systems are still functioning but the body’s increasing reliance on the anaerobic glycolysis system results in LA and H+ levels that curtail the activity. Figure 2.16 on the preceeding page indicates there is no exact physical state at which the lactate threshold occurs. It will differ with each individual, the individual’s state of fitness and the intensity of the activity. However, some indicators (which vary in their precision) provide coaches and athletes with a means of assessing the effort required by a work-out (table 2.3). Table 2.3 Ways of determining the lactate threshold Method Determinant 1. Percentage of maximum heart rate Untrained athlete — around 60 per cent Trained athlete — around 90 per cent 2. Percentage of maximum oxygen uptake Untrained athlete — around 50 per cent Trained athlete — around 80 per cent 3. Blood lactate levels Untrained athlete — 4 mmol/L Trained athlete — more than 4 mmol/L 4. Conversation during exercise Ability to talk continues, but extended conversation is uncomfortable. 5. Respiration Breathing rate is still comfortable at the onset of blood lactate accumulation but becomes more rapid as effort continues past it. Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity • Muscular fatigue mechanisms, specifically fuel depletion, metabolic by-products, and dehydration Key skills • Describe the interplay of the energy systems, using correct terminology. • Analyse the relationship between energy systems and physical activity. • Perform, observe, analyse and report on laboratory exercises designed to explore the relationship between energy systems during physical activities. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Activity 7 Laboratory report The aerobic glycolysis system Select two high-level endurance athletes from the class and obtain a medical clearance for each. a Carry out an aerobic power laboratory test, such as the Multi-Stage Fitness Test, or the Phosphate Recovery Test (see chapter 6). b Ensure you can record accurate heart rates. c Predict when the onset of blood lactate accumulation is likely to occur for each of the two subjects. d Have the subjects perform the test to exhaustion, recording as many body responses as possible during the test. e Try to pinpoint when the onset of blood lactate accumulation occurs. Give reasons for your decision. f Try to pinpoint when the lactate threshold occurs for each. How long after this was each individual able to continue working? g Assess the value of the test and answer questions your teacher will prepare. Some possible areas to investigate include: • levels of oxygen consumption during the test • the percentage contributions of each energy system • differences in the onset of blood lactate accumulation for each subject • reasons for respiration rates and other body responses to the test. LIVE IT UP 2 76 1_61_02472_LIU2ch2.indd 76 2/12/05 9:18:13 AM Most sports participants specifically target their lactate threshold in training in order to improve their aerobic delivery of energy (by reducing or delaying their reliance on anaerobic metabolism). As a result, trained athletes can generally tolerate higher levels of lactic acid in their working muscles (see chapters 7 and 9 for more detail). Lactic acid removal Existing exertion levels determine the rate of lactic acid removal. An active recovery provides the best conditions, with exertion levels less than the level of the lactate threshold and with a heart rate ideally 15–30 beats per minute lower than that at the lactate threshold. With blood flow greater than at rest levels, the blood flow through the muscle capillaries is still substantial enough to disperse lactic acid. The bulk of lactic acid is converted back to pyruvic acid then oxidised inside the mitochondria via the citric acid cycle, ultimately creating new ATP supplies. During exercise and depending on the aerobic levels of activity, lactic acid can serve as a ‘metabolic precursor’ (or energy source). If there is ‘spare’ oxygen due to the aerobic exercise levels being below the lactate threshold, the body can clear lactic acid through neighbouring muscle fibres in less active muscle groups, as well as through the heart, liver and spleen. Once exercise is finished, the liver can also reconvert lactic acid to glycogen. Lactic acid levels during changes in exercise intensity Increases in exertion levels may occur at different times in sport, such as: • with tactical surges during 1500 to 10 000-metre athletic races • while pushing hard up a hill during a triathlon cycle leg • when running ‘on the ball’ in Australian Football • while closely following a talented wing attack for half of a netball game. With sudden increases in intensity, the quickest responding energy system is anaerobic glycolysis. When this increase in exertion is passing the lactate threshold the quick accumulation of lactate and H+ will require a following rest period to allow levels to fall below the threshold. Depending on how long each excursion is beyond the lactate threshold, this pattern has to continue throughout the activity for the athlete to achieve optimal performance. The aim is to avoid too much lactate and H+ accumulation which demands longer periods of rest before the effort can be repeated. Key knowledge • Muscular fatigue mechanisms, specifically fuel depletion, metabolic by-products, and dehydration Key skills • Analyse the relationship between energy systems and physical activity. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Activity 8 Structured questions The onset of blood lactate accumulation 1 What sporting examples (other than those detailed above) exemplify times when athletes reach the lactate threshold? 2 How is each example a debilitating influence on the performer’s ability to complete the event? 3 Can athletes train to delay the lactate threshold? CHAPTER 2 ENERGY SYSTEMS 77 1_61_02472_LIU2ch2.indd 77 2/12/05 9:18:14 AM Lactate as an energy source Figure 2.17: Blood lactate levels with varying levels of intensity from the beginning of exercise. Note the existence of blood lactic acid before exercise begins. Recent research has focused less on the inhibiting effects of lactic acid and more on the ability of the body to metabolise lactic acid as a source of ATP production for muscular effort. When the demand for ATP reduces, lactic acid can be broken down by the body to create replenished ATP supplies. This situation of sufficient oxygen availability is most readily found during team games or long-distance endurance events that may be punctuated by spurts of anaerobic effort. For example, triathlons, marathons, long-distance athletic track events, or cycling tours. These sporting situations will see high level anaerobic efforts followed by a recovery phase of aerobic effort. As long as this ‘recovery’ level is below the individual’s lactate threshold, then the excess oxygen will be able to metabolise the extra lactic acid accumulated from the burst of higher effort. Accompanying this change of emphasis has been greater acknowledgement of the inhibiting effects of increased muscle acidity during anaerobic work. The rising levels of hydrogen ions (H+) within the anaerobically working muscle are now recognised as the more significant inhibitor to effective muscle contraction. Increased acidity upsets the normally smooth interaction between the actin and myosin within the muscle cell’s sarcomere. It also interferes with energy generating chemical pathways of each of the energy systems. Onset of exercise Line A: start of exercise, which is maintained at levels lower than lactate threshold Line B: exercise intensity at levels above that of the lactate threshold Line C: exercise intensity at levels at the lactate threshold Line D: exercise intensity at levels oscillating above and below the OBLA, given the competition demands and available aerobic recovery periods B C D A Figure 2.18 Cadel Evans in the 2005 Tour de France — controlling his lactate threshold is of the utmost importance. LIVE IT UP 2 78 1_61_02472_LIU2ch2.indd 78 2/12/05 9:18:15 AM The article in figure 2.19 reassesses the role of lactic acid as a cause of muscle fatigue. Read the article and discuss its ideas as a class. Evidence mounts that lactic acid helps, not hinders, athletic performance By Justin Kemp and Damian Farrow Sally Robbins stopped rowing because of it. Paula Radcliffe ended her Olympic marathon due to it. And the Australian 4 x 400 metres relay team claims that a silver medal helped cure its ill-effects. One chemical appears to be solely responsible for all the fatigue and discomfort felt when exercising to the limit — lactic acid. But is this really true? There are many types of fatigue and the causes vary depending on the duration and intensity of the activity. Acute alterations to nerve and muscle function, to the metabolic environment in cells, to the availability of fuel for energy supply and to hormonal levels may all act to slow us down. The brain, too, plays its part in perceiving these signals and acting to protect the body from damaging over-exertion. But because lactic acid production increases with ever-heavier exercise, it has become the common scapegoat to explain declines in performance at the muscle level. When lactic acid is generated in human cells, it immediately separates into two components: (1) the lactate ion, and (2) a hydrogen ion (which reflects an increased acidosis). These two are often touted to inhibit the force and speed of muscle contraction, disrupt the ionic balance of the cells and slow the work-rate of the muscle’s energysupplying pathways. Many studies have explored the impact that both lactate and acidosis has on muscle performance and this work is now trumpeting the virtues of lactic acid. When lactic acid is produced during exercise and transported from working muscles into the bloodstream as lactate, the heart, neighbouring and distant muscle fibres and even the brain can use it as an energy source. Furthermore, the liver and kidney can convert lactate back to glucose, demonstrating that lactate is not the negative by-product of metabolism that it is so often labelled. It is actually a mobile fuel appreciated by other tissues. In truth, lactate is an indispensable intermediary molecule involved in many physiological processes, including a role in maintaining muscle force. Professor Graham Lamb’s team at La Trobe University has shown that high concentrations of lactate have little inhibitory effect on activation and contraction within single muscle fibres. Meanwhile, scientists at Aarhus University in Denmark demonstrated that lactic acidosis may even protect against potential losses in the ability to activate muscles (called muscle excitability) and enforce output that can take place because of inevitable potassium escape from exercising muscle fibres. A subsequent collaboration between these Danish and Australian research teams also has provided evidence that acidosis might block the movement of chloride across muscle fibre membranes — a mechanism that would enhance the excitability of the fibres. Moving from single muscle fibre experiments to regular exercise the Medical School of Hanover in Germany recently reported that an induced acidosis did not negatively affect the contraction speed of muscles involved in hand-grip exercise. Moreover, a Swedish group has shown that some of the experiments that implicated acidosis in muscle fatigue do not hold when these same trials are performed at body temperature. Some scientists even suggest that lactate production decreases muscle acidosis. The accumulation of lactate in the muscle and blood during exercise might still be a good marker to indicate the onset of fatigue, but this in no way declares that lactic acid causes muscle fatigue. There is now overwhelming evidence from myriad experimental protocols expounding lactate as being not harmful, and even beneficial, to exercise performance, compared with limited evidence to the contrary. Source: The Age, 4 September, 2004 Figure 2.19: Lactic acid reassessed CHAPTER 2 ENERGY SYSTEMS 79 1_61_02472_LIU2ch2.indd 79 2/12/05 9:18:17 AM CHAPTER REVISION Key knowledge • Characteristics and interplay of energy systems for physical activity and recovery in relation to duration, intensity and type of activity • Fuels required for physical activity and the conversion of food to energy • Muscular fatigue mechanisms, specifically fuel depletion, metabolic by-products, and dehydration Key skills • Describe the interplay of the energy systems, using correct terminology. • Analyse the relationship between energy systems and physical activity. • Perform, observe, analyse and report on laboratory exercises designed to explore the relationship between energy systems during physical activities. • Identify and explain the relationship between physical activity, muscular fatigue and recovery. Chapter summary • The energy for physical activity is released by the catabolism (breaking down) of adenosine triphosphate (ATP). This energy source is stored in only small amounts within muscles. • ATP is produced via three energy pathways: — the phosphate energy system, which uses phosphocreatine to create new ATP supplies without using oxygen — the anaerobic glycolysis energy system, which uses glycogen but no oxygen — the aerobic energy system, which uses oxygen and primarily glycogen and fat (and protein under extreme conditions) to create ATP. • The phosphate energy system can create ATP very quickly, with a major energy contribution to powerful exertions of up to around 10 seconds’ duration. It depletes quickly, taking around 3–5 minutes to fully replenish. • The anaerobic glycolysis system takes longer to create ATP. It is the major contributor to high-level exertions of 10–30 seconds, but creates lactate and hydrogen ions as by-products. The lactate threshold is the stage when lactic acid concentrations within the blood reach the level at which continued high-level muscle activity cannot continue. It can take up to 60 minutes to restore lactic acid to resting levels. • The aerobic glycolysis system becomes the major contributor to muscle activity from around 30 seconds into a sustained sporting performance. It relies on an efficient circulo-respiratory system. The creation of ATP within the muscle occurs in the mitochondria. Review questions 1. Define in your own words the key terms listed below, all of which appear in this chapter: When you have finished, check your definitions with those in the glossary on page 435. adenosine triphosphate aerobic energy anaerobic glycolysis carbohydrate citric acid cycle electron transport chain energy substrates fat fat oxidation free fatty acids glucose glycogen hydrogen ions lactate lactate threshold lactic acid mitochondria mmol/L of LA muscle acidity OBLA phosphate energy system phosphocreatine protein steady state triglycerides 2. Construct pie charts showing percentage energy contributions of each of the three energy systems for the following activities: (a) walking (d) 1500-metre athletic race (b) a slow jog (e) 10 000-metre athletic race (c) 400-metre athletic race (f) the Hawaii triathlon. Give reasons for your energy breakdowns. LIVE IT UP 2 80 1_61_02472_LIU2ch2.indd 80 2/12/05 9:18:18 AM Note: Questions 3 and 4 review material is not directly assessable under the 2006–9 VCAA Physical Education study design. 3. (a) To which myofilament are the cross bridges attached? (b) How do the cross bridges facilitate muscle contraction? 4. (a) On the following diagram of a sarcomere at rest, where do these features appear? Z line A band I band H zone Sarcomere CHAPTER 2 CHAPTER REVISION (b) What happens to each of these features during muscle contraction? 5. (a) Calcium is released during muscle contraction. From where is it released? (b) How does the release of calcium assist muscle contraction? 6. Name activities or sports best suited to each of the bars within the graphs in figure 2.14 (page 74). 7. Study the bar graph in figure 2.15 (page 75). (a) Why is exercise at 25 per cent of VO² max more useful for weight control than exercise at higher intensity levels? Give the physiological reasons. (b) Why does the carbohydrate proportion increase so markedly at 85 per cent of VO² max? 8. Study the graph in figure 2.16 (page 75). (a) Draw the graph and add the probable lactate threshold for an elite AFL player (in mmol/L of blood) to the vertical axis. (Use table 2.3 on page 76 as a guide.) (b) Why does the contribution of anaerobic glycolysis to ATP production increase after the athlete reaches the lactate threshold? (c) Define the ‘lactate threshold’. How is the term ‘onset of blood lactate accumulation’ different? 9. Study the graph in figure 2.17 (page 78). (a) What different sporting activity is representative of each situation in lines A–D? (b) Why do you think that not all the lines begin at the junction of the X and Y axes? (c) Why does line A have a hump? 10. Examine the data in figure 2.20 on the following page, showing times for the four individual 100-metre splits of the three medallists in the women’s 400-metre event at the Sydney Olympics. Answer the following questions: (a) State the physiological factors that explain Cathy Freeman’s much faster third and fourth 100s when compared with Graham and Merry. (b) Which energy system is most important to the runners over the first 50 metres? (c) Give reasons for your answer to question (b) above. (d) From the data in table 2.4, use evidence to show at what point you believe lactate levels have become an influencing factor in the run. ENERGY SYSTEMS 81 1_61_02472_LIU2ch2.indd 81 2/12/05 9:18:19 AM CHAPTER REVISION Figure 2.20: Heart rate at various exercise intensities Source: Reproduced from the Herald Sun, 26 September, 2000 Table 2.4 Data from the race 100m No. 1 No. 2 No. 3 No. 4 Total Freeman 12.30 11.78 12.06 12.97 49.11s Graham 12.14 11.56 12.30 13.58 49.58s Merry 12.32 11.48 12.28 13.64 49.72s (e) Define OBLA. Is it the reason for athletes to stop their performance efforts? (f) Understanding that there is a ‘usual’ circulatory system lactic acid level where the lactate threshold is said to occur in most people, what could Freeman’s lactic acid levels have been at the end of the race? Give your answer in mmol/L. (g) What is the ‘usual’ level of LA for the lactate threshold to occur? Give your answer in mmol/L. (h) Discuss the probable differences in the 400-metre race between Freeman’s reaction to the OBLA and an unfit individual’s reaction. (i) Draw three pie charts. In the first, give your estimates of percentage contributions from each of the three energy systems for the first 200 metres of the race. In the second pie chart, give the estimated percentage contributions for the second 200 metres of the race. In the third, give the percentage contributions from each of the three energy systems for the total race. (j) Provide reasons for the divisions in each of the pie charts in (i) above. 11. (a) Describe the intensity and duration of a sporting activity where phosphocreatine is the predominant fuel source. (b) Name a specific sporting activity/situation that clearly illustrates the use of phosphocreatine as the predominant fuel source. (c) List one advantage and one disadvantage in using phosphocreatine as a fuel. LIVE IT UP 2 82 1_61_02472_LIU2ch2.indd 82 2/12/05 9:18:20 AM 12. (a) Describe the intensity and duration of a sporting activity where anaerobic glycolysis is the predominant fuel source. (b) Name a specific sporting activity/situation that clearly illustrates the use of anaerobic glycolysis as the predominant fuel source. (c) List one advantage and one disadvantage in using anaerobic glycolysis as a fuel. Figure 2.21: AFL player Luke Ball displays the importance of all fitness components and energy systems to his team game. Websites www.anatomy.usyd.edu.au/mru/lectures/lecture2.pdf Anatomy 2001 Muscle/ Mobility Structure www.sport-fitness-advisor.com/anaerobicthreshold.html Anaerobic Threshold . . . The Key to Developing Elite Endurance www.e-muscles.net CHAPTER REVISION 13. Use your knowledge of team games and the way in which players need to perform phosphate efforts repeatedly over 1–2 hours total playing time. Reflect on the photo of AFL star Luke Ball in figure 2.21, using it as a prompt to add to your own experiences. Then answer the following question: How does Ball rely on all three energy systems to both maximise his skill and power, and to run out the entire four quarters of the game? e-Muscles.net http://sln.fi.edu/biosci/systems/systems.html ‘You Have to Have a System’, The Heart: An Online Exploration www.lactate.com/eslact1c.html Lactate Physiology and Sports Training http://.home.hia.no/~stephens/lacthres.htm The Lactate Threshold NISMAT Exercise Physiology Corner: A Primer on Muscle Physiology Anaerobic Threshold . . . The Key to Developing Elite Endurance www.nismat.org/physcor/muscle.html web.indstate.edu/thcme/mwking/muscle.html ‘Muscle Biochemistry’, The Medical Biochemistry Page www.predator.pnb.uconn.edu~wwwpnb/virtualtemp/muscle/exercise-folder/muscle.html Muscle Metabolic Systems in Exercise http://muscle.ucsd.edu/musintro/struct.shtml ‘Skeletal Muscle Structure’ Muscle Physiology Homepage www.anatomy.usyd.edu.au/mru/lectures/lecture1.pdf www.brianmac.demon.co.uk/siteindx.htm Skeletal muscle structure Sports Coach Page Index A–Z CHAPTER 2 ENERGY SYSTEMS 83 1_61_02472_LIU2ch2.indd 83 2/12/05 9:18:21 AM