Energy systems and physical activity

Transcription

1 CHATER 7 Energy systems and physical activity CHATER 7 The energy for muscular contractions comes from adenosine triphosphate, which is found in several sources including our food and drink. It may be released from carbohydrate, fat or protein, 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 towards the production of adenosine triphosphate, along with their relative characteristics. The lactate threshold is a major concept in energy system theory.

2 Assessment tasks Assessment tasks Topics age Written report Diet assessment (activity 2) 211 Oral presentation Multi-stage fitness test (activity 4) 218 Laboratory reports hosphate recovery times (activity 3) Multi-stage fitness test (activity 4) Step test (activity 5) Data analysis hosphate recovery times (activity 3) 217 Case study analysis Aerobic power test (activity 7) 225 Multimedia presentation Activity analysis phosphate efforts (activity 6) 223 Report on participation in physical activity Basketball analysis (activity 1) 211 Test Review questions 226 CHATER 7 After completing this chapter, students should be able to: identify the three major energy systems that interplay during physical activity describe the various ways in which adenosine triphosphate (AT) is created within the three energy systems explain the advantages and limitations of each of the three energy systems analyse how sports performance is controlled and predicted by their reliance on each of the three energy systems outline the causes of fatigue including the lactate threshold, energy substrate depletion and inefficient recovery.

3 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), the body needs energy sources that will 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. triphosphate The chemical compound adenosine triphosphate (AT) provides the energy that allows muscular effort. AT is the energy source for all muscular effort, whether for a small subconscious movement such as the blinking of an eye or a planned repetitious effort in weight training (see chapter 9, Live It Up 2, second edition). Sources of AT AT 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, minerals and water. AT can be created from carbohydrate, fat and protein. Chapter 11, Live It Up 2, second edition more fully explores 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 AT 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, fat (as either triglycerides or free fatty acids) usually contributes to AT 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. During rest conditions, fat produces the majority of the required AT. rotein rotein only minimally contributes to AT production. In extreme circumstances (such as starvation or ultra triathlon/marathon events) when the body has severely depleted its supplies of carbohydrate and fat, protein can become a viable source of AT. 210 LIVE IT U 1

4 Table 7.1 The body s storage of food fuel Key knowledge The cardiorespiratory system: structure of the heart and lungs, mechanics of breathing, gaseous exchange, blood vessels, blood flow around the body at rest and during exercise Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Food fuel Stored as Site Carbohydrate Fat rotein Activity 1 Glucose Glycogen Adipose tissue (storage of excess carbohydrates) Free fatty acids Triglycerides Adipose tissue Muscle Amino acids Report on participation in physical activity Blood Muscle and liver Around the body Blood Muscle Around the body Skeletal muscle Body fluids Basketball analysis As a class, after an appropriate warm-up, play a hard game of basketball or netball. Hand out to-scale court drawings on which player movements can be plotted. 1. Have the class organised into these work groups: players body parameter recorders; paired off one-on-one with the players games analysis recorders; paired off one-on-one with the players. 2. lay a number of 7 10 minute playing segments, each with an intervening 5 minute break. During the play, the games analysis recorders are to plot how far their partner has sprinted, jogged, walked and for how long they stood still in the playing segment. 3. During the breaks, the body parameter recorders are to talk with, assess and record their partners physical responses, including: heart rates (polar heart rate monitors will be useful for this, or do it manually with 10 second pulse counts) respiration rates observable perspiration amounts verbal reports of fatigue levels (easy, bit puffed, tiring, struggling, had it...). 4. In your work groups, compile your results and address the following issues: a resent your findings in hard copy tables and/or a multimedia presentation. b How far did your player sprint, jog and walk? c What percentage of time did he or she spend in each of sprint/jog/walk, and for how long were they stationary? d lot their physical responses to the exercise segments against the other players. e Establish a priority list of perceived fitness among the players. f List the bases for your decisions in question e. g List the information that the class has established from this exercise that cover fitness, fatigue and energy. Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Activity 2 Written report Diet assessment Record your total diet for three days. Estimate the percentages of carbohydrates, fats and protein by using packet labelling and nutrition guides supplied by your teacher. Have a class discussion to establish how you could improve your diet to meet your energy needs. CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 211

5 Energy from AT AT is stored in limited quantities within muscle, so each muscle fibre must be able to create its own from the food fuels. Figure 7.1 illustrates how the metabolism of food creates AT which then provides energy for muscular exertion. AT Food Energy Energy Muscle activity AD + Figure 7.1: Energy for muscular activity from food to AT to muscles AT 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 (AD) (see figure 7.1). This process is reversible: figure 7.2 shows how AD can become AT. This reversal can occur continually during the activity as long as sufficient energy substrates are available. Depending on the type of physical activity (see chapter 8), energy substrates include phosphocreatine, glucose, glycogen, lactic acid, fat, protein and oxygen. These are substances the body can use to create AT. A muscle fibre stores only a small amount of AT, so the force and duration of a muscular effort is only as effective as the AT replenishment process. During and after physical exertion, the body uses several methods of recovery to rebuild used supplies of AT and food fuels. 212 LIVE IT U 1

6 Brain CNS AT for physical activity 1 Muscles have stores of AT ready for activity. Muscles 2 Movement is initiated by a message from the Central Nervous System (CNS) to the muscle. 3 The muscle releases calcium salts into the muscle depths that activate AT. 4 AT loses one of its three phosphate molecules and thereby releases energy for muscle contraction. 7 5 Muscles contract. 6 AD amounts build as AT diminishes. 3 7 During aerobic effort or during rest, spare oxygen allows the reattachment of loose with the AD, thus creating more AT More AT is constantly created during rest or during the activity depending on the intensity of the exercise. Energy 6 4 Figure 7.2: The cycle of AT being broken down for muscle movement, consequentially creating AD, then being reconstituted as AT with the presence of oxygen 5 CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 213

7 Energy for rest and activity The body can create energy (AT) under two main conditions: rest conditions, where there is sufficient oxygen available for the body to continue to function at a resting level 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. AT 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 AT from fat stores within the muscle and elsewhere in the body. Fat is a much richer energy source than carbohydrates. To release this energy, the body must use much more oxygen than it would in activating the supplies of AT from glucose. When at rest, you have an abundant supply of oxygen which is above the body s metabolic demands. The other third of AT 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 7.8). 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 AT production. AT production during activity Activity in physical education is a broad 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 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) are unable to meet this immediate demand, so the body uses two energy pathways to create AT anaerobically (i.e. without oxygen). These anaerobic pathways produce AT quickly and powerfully, but they have three disadvantages: they produce relatively small amounts of AT 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 AT aerobically because the body s ability to use oxygen can meet the muscles demands for extra oxygen for greater AT production. This aerobic pathway has opposite qualities to those of the two anaerobic systems: it can produce AT 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 AT under these varying levels of physical activity via three energy pathways: the phosphate energy system, the anaerobic glycolysis system and the aerobic system. 214 LIVE IT U 1

8 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 7.3 illustrates the overlapping nature of the three energy systems that 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. hosphate energy system The phosphate energy system provides the bulk of AT during powerful or explosive efforts. Such efforts may be once-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 is closely linked with several fitness components (see chapter 5, Live It Up 2, second edition). muscular strength anaerobic power agility muscular power speed reaction time. 100 Energy contribution (%) Anaerobic glycolysis Aerobic energy Figure 7.3: A graphic interpretation of the three energy systems and their periods of prominence 0 0 hosphate energy erformance time (seconds) 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 AT. The phosphate energy system relies on muscle stores of both AT and a chemical compound called phosphocreatine. If the activity requires a maximal effort for 5 10 seconds, such as an elite 100-metre sprint event, then stores of AT and phosphocreatine in the working muscles jointly create most of the maximal effort for that activity. After about 10 seconds of efforts, the muscles stores of AT and phosphocreatine are greatly depleted. Thus, with critically low stores 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 AT from AD, and to reconstitute phosphocreatine from the broken phosphate and creatine molecules remaining after the sprint (see figure 7.4). Following a 10-second maximal effort, the body can take around 3 5 minutes to fully restore the AT and phosphocreatine supplies to pre-exercise levels within the working muscles. If the effort was less than 10 seconds, then the recovery time to pre-exercise levels is faster than 3 minutes. (Chapter 4, Live It Up 2, second edition contains more detail on this recovery process.) CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 215

9 C 6 C 1 The phosphate system 1 The power athlete at the start of the event, muscles primed and full of AT and C stores. 2 At the starting gun, the maximal explosive effort to leave the starting blocks immediately uses up some of the stored AT in the muscles, resulting in AD. Energy 3 The muscle stores of C split, releasing energy. 5 C Energy 4 This energy allows the single phosphate molecules left from the spent AT to be reattached to the AD creating more AT that allows the maximal effort to continue. 5 This replenishing process continues while the athlete completes the race at maximal effort. 6 The athlete crosses the finish line with muscle stores of AT and C depleted. 2 C C 4 C Energy C 3 Figure 7.4: The cycle of AT being broken down and resynthesised for powerful muscle movement centres around the energy from C splitting 216 LIVE IT U 1

10 Key knowledge The cardiorespiratory system: structure of the heart and lungs, mechanics of breathing, gaseous exchange, blood vessels, blood flow around the body at rest and during exercise Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Activity 3 Laboratory report and data analysis hosphate recovery times As a class, choose half the class to thoroughly warm up and then attempt a series of 25-metre swimming sprints. Allow gradually reduced recovery periods after each sprint: 5 minutes, 3 minutes, 1 minute and 10 seconds. Each subject should take their heart rate for 10 seconds after each sprint. If you are not a test subject, help organise and record the sprints. 1. Graph (by plotting it on graph paper or by using graphing software) and discuss the results. 2. Write a report in which you explain the peak time for the phosphate energy system, its required recovery period and how the laboratory demonstrated the theory. Anaerobic glycolysis system The anaerobic glycolysis system is also known as the lactic acid system. This system mainly provides the bulk of AT production during highintensity, sub-maximal efforts. It may also become the dominant producer of AT during repeated phosphate efforts which have insufficient recovery time to allow full phosphocreatine replenishment. Muscle stores of glycogen are anaerobically broken down during effort to release energy for AT to be resynthesised from AD. The anaerobic glycolysis system operates as the dominant supplier of AT in the period from around 10 seconds of maximal effort to around 60 seconds. Most recent studies suggest that the overlap period when the body switches from using the anaerobic glycolysis system as the dominant AT producer to using the aerobic system could start as early as 30 seconds into high-level, sub-maximal activity (see figure 7.3). The anaerobic glycolysis system is closely linked with several fitness components (see chapter 5, Live It Up 2, second edition): anaerobic power local muscular endurance speed muscular power. CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 217

11 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. Because the anaerobic system operates without oxygen being used for AT production, lactic acid (LA) is produced as a by-product. This affects the muscles ability to contract and creates fatigue in the performer. If the performer tries to continue exercising at the same anaerobic intensity, the levels of lactic acid increase and will cause the individual to either slow down or stop. As the individual tries to continue exercising at this high anaerobic intensity while fighting the fatigue caused by the lactic acid, they will reach what is known as their lactate threshold. This is the level at which the lactic acid levels prevent their ability to continue working at the same intensity. During 20 minutes of a football or netball game, an involved player may carry out over 100 power (or phosphate) efforts. Even if adequate oxygenrich 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 AT production, and the next quickly available system (anaerobic glycolysis) takes over as the dominant AT supplier. During a 400-metre run, lactate accumulation affects the runner during the home straight but can generally be endured until the race finishes. A team game is quite a different situation: the lactate threshold cannot be ignored. Figure 7.5: Jana ittman running another 400-metres hurdles race. Her efforts produce large amounts of lactic acid. Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Activity 4 Laboratory report and oral presentation Multi-stage fitness test As a class undertake the multi stage fitness test (see chapter 6, Live It Up 2, second edition). 1. Stop when you reach what you think is your lactate threshold. 2. Record your HR at this time. 3. Note the reasons why you have picked this stage of the test. 4. Could you have kept running? Give some reasons. 5. For how long? 6. Was the level you reached the best you have done for this test? 7. Write up your responses to the class s efforts and share these with the class in an oral report. 218 LIVE IT U 1

12 LA 6 AD + glycogen O 2 AT 1 The anaerobic glycolysis system 1 On blocks at start of 400 m race. 2 At 15 20m point. AT C system is depleted. Anaerobic glycolysis system now becoming dominant AT supplier. AD + C AT 5 LA AD + glycogen No O 2 AT 3 End of back straight at 200 m mark. Cruising, feeling good. LA increasing in blood stream, but not noticeable. 4 Entering home straight, about 80 m from home. Increasing LA levels beginning to be uncomfortable. 5 Building LA levels do not prevent finishing the race, but do cause a slowing down during the last 80 m of the race. 6 Much puffing after the race helps reduce LA levels to resting values within the next half hour or so. C AD + glycogen No O 2 AT 2 LA LA 4 AD + glycogen No O 2 AT 3 Figure 7.6: Anaerobic glycolysis is best exemplified in the 400 m run. It provides most of the needed AT but produces lactic acid. CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 219

13 Figure 7.7: Aerobic glycolysis is best exemplified in any longer aerobic effort. It provides the vast bulk of the required AT. Aerobic energy system The aerobic energy system is also known as aerobic glycolysis. 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 submaximal efforts. Aerobic glycolysis, as with all the energy systems, contributes to AT production under all conditions. However, it contributes the majority of AT during continuous sub-maximal activities that go beyond 1 minute. With the rich oxygen supplies in the aerobic system, fat is able to become a significant contributor to AT production. Fat requires a complex series of reactions that depend on oxygen within the muscle cell s mitochondria. rotein is similarly metabolised for AT production, but only under extreme conditions. The body s supply of fat exceeds even the physical requirements of a highly trained athlete, so the aerobic system could theoretically operate for an unlimited work period Energy 5 AD + glycogen O 2 AT LA The aerobic glycolysis system 1 Start of 20 minute cross-country race. 2 Low sub-maximal effort with HR around per cent of maximum. 3 Sufficient O 2 levels allow AT to be continuously replenished from AD. 2 4 LA 4 Any periods of acceleration or hill work will increase LA levels, but are generally controlled by following periods of lower exertion where O 2 supplies become plentiful again. 5 At end of race, fatigue is generally from joint fatigue, dehydration, mental fatigue, higher than normal LA levels or reduced muscle glycogen. AD + glycogen O 2 AT AD + glycogen O 2? AT LIVE IT U 1

14 Mitochondrion Glycogen Figure 7.8: The mitochondrion carries out aerobic glycolysis, involving glycogen breakdown with oxygen present. Also, both fat and protein may be metabolised. Glucose AT yruvic acid Fat Citric acid cycle rotein Carbon dioxide AT Oxygen Hydrogen Electron Water transport chain Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis The cardiorespiratory system: structure of the heart and lungs, mechanics of breathing, gaseous exchange, blood vessels, blood flow around the body at rest and during exercise Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Activity 5 Laboratory report Step test If they are available use olar HR monitors. If not, work in pairs and take HR manually. Sit quietly on some benches in the physical education centre at school, and put on a heart rate monitor. Check the monitor is displaying your heart rate. Do not talk or walk around. Concentrate on breathing slowly and evenly. Take note of your heart rate after sitting quietly for three minutes. Record your heart rate. Begin the test under your teacher s directions: step up and down on the bench at a set rhythm that allows you to complete a full stepping sequence each five seconds, or 20 sequences per minute. ut your left foot up, right foot up, left foot down, right foot down... and so on. When both legs are on top of the bench, both legs should be straight. Continue stepping until told to stop and then sit down on the bench. After 5 10 seconds record your heart rate and continue to record every 30 seconds for five minutes. Record all measurements on the sheet. Complete the table below with your results after you finish exercising. Graph your results. Answer the following questions: 1. What was your maximum heart rate at the end of the step-up exercise? 2. On the same graph draw the results of another subject. Clearly label both graphs. 3. Compare the two graphs. Which subject s heart rate dropped the greatest distance? 4. Who do you think is fitter for this exercise? 5. What evidence could you give to support this? 6. What factors control resting, exercise and recovery heart rates? Time 00 sec 30 sec 1.00 min 1.30 min 2.00 min 2.30 min 3.00 min 3.30 min 4.00min 4.30 min 5.00 min Heart rate CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 221

15 Table 7.2 Summary of the three energy systems Characteristic 1. Energy source for AT production 2. Duration of dominant energy production 3. Recovery time until repeat effort 4. Limiting factor when operating maximally 5. Intensity and duration of activity where the system is the dominant AT provider 6. Specific sporting examples hosphate energy hosphocreatine Anaerobic glycolysis Carbohydrate Glycogen Aerobic glycolysis Carbohydrate Fat rotein 5 10 Seconds Seconds >60 seconds hosphocreatine replenishment: 3 5 minutes Depletion of phosphocreatine Maximal intensity (>95% max hr) and duration of 1 10 seconds 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 forwardcentre back contest Removal of lactic acid to rest levels: With active recovery: 95% removal: 30 minutes Lactic acid accumulation High, sub-maximal intensity (85 95% max hr) and duration of seconds m in athletics 50 m swim consecutive basketball fast breaks high intensity 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 Restoration of body glycogen stores: 6 48 hours Lactic acid accumulation Lower glycogen stores Dehydration Sub-maximal intensity (<85% max hr) and duration of >30 seconds marathon cross-country skiing triathlon AFL mid field hockey wing all elite team players rowing 2000 m race water polo game 7. 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 mowing lawn dancing ironing studying 222 LIVE IT U 1

16 Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Key skills Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Activity 6 Multimedia presentation Activity analysis phosphate efforts Watch a replay of any high-level team game, then assign groups to record all phosphate efforts by the players. 1. Assess the average length of each effort and the average recovery time between each. 2. Determine the relative importance of each of the three energy systems to the game. 3. Display your percentages in pie charts and as a oweroint presentation. AT production different exertion conditions The length and intensity of physical exertion determine which of the energy systems is the dominant contributor to AT production (figure 7.9). As the activity time increases, the influence of the aerobic system on AT production also increases. However, the relative contribution of each of the three energy systems varies according to the intensity and duration of the activity. AT Creatine-phosphate 6.3% 8% Anaerobic glycolytic Aerobic glycolytic Aerobic lipolytic 44.1% 50% 50% 65% 50% Figure 7.9: The average energy contributions of different energy systems during high-intensity competition Source: Burke, L. and Hawley, J. 1998, eak performance: training and nutritional strategies for sport, Allen and Unwin, St Leonards, p % 6 seconds 30% 20% 30 seconds 50% 60 seconds 35% 120 seconds 92% 1 hour 50% 4 hours CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 223

17 Onset of blood lactate accumulation OBLA is the acronym for the onset of blood lactate accumulation. At rest, everyone has lactic acid (LA) in their muscles. It is only when exercise begins that the muscular levels of LA begin to rise. If the exercise or activity is anaerobic in nature, then the levels of LA rise more significantly. At the early stages of anaerobic work, the rising muscular concentrations of LA easily flow from the working muscles through the capillary walls into the circulatory system. This increase in blood levels of LA 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 athletes. When these readings are combined with an athlete s record of physiological responses to exertion, training can be tightly geared around his or her lactate threshold. Lactate threshold 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 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 untrained people, the lactate threshold is usually around 4 mmol/l, (mmol/l the measure of how many units of LA are present in one litre of blood). Trained athletes can increase their tolerance to LA accumulation and are able to continue effective performance or training with much higher lactate 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. 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 lactic acid levels that curtail the activity. Figure 7.10 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 7.3). Figure 7.10: The aerobic and anaerobic contributions to AT production as exercise intensity increases. The lactate threshold is the point at which lactic acid production affects performance. LA accumulation mmol/l 4 Exercise intensity Anaerobic systems Aerobic system 224 LIVE IT U 1

18 Table 7.3 Ways of determining the lactate threshold Method 1. ercentage of maximum heart rate Determinant Untrained athlete around 60% Trained athlete around 90% 2. Blood lactate levels Untrained athlete 4 mmol/l Trained athlete more than 4 mmol/l 3. Conversation during exercise Ability to talk continues, but extended conversation is uncomfortable. 4. Respiration Breathing rate is still comfortable at the onset of blood lactate accumulation but becomes more rapid as effort continues past it. Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Activity 7 Case study analysis Aerobic power test Select two high-level endurance athletes from the class and obtain a medical clearance for each. 1. Design an aerobic power laboratory test on bikes or treadmills that can be continued to maximal levels. 2. Ensure you can record accurate heart rates. Use olar HR monitors. 3. redict when the onset of blood lactate accumulation is likely to occur for each of the two subjects. 4. Have the subjects perform the test until they have to stop, recording as many body responses as possible during the test. 5. Try to pinpoint when the onset of blood lactate accumulation occurs. Give reasons for your decision. 6. Try to notice when the lactate threshold occurs. 7. 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. 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 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 AT inside the mitochondria creating new AT supplies. Once exercise is finished, the liver can also reconvert lactic acid to glycogen. The body also deals with small amounts of lactic acid through respiration, perspiration and excretion. CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 225

19 CHATER REVISION Key knowledge Introduction to aerobic and anaerobic energy systems, including aerobic and anaerobic glycolysis The cardiorespiratory system: structure of the heart and lungs, mechanics of breathing, gaseous exchange, blood vessels, blood flow around the body at rest and during exercise Key skills Use correct terminology to describe the role of the body systems at rest and when undertaking physical activity. Observe and record how the body systems function during physical activity. Identify and discuss the range of acute effects that physical activity has on the body. erform, observe, analyse, evaluate and report on laboratory exercises related to the body systems. Chapter summary The energy for physical activity is released by adenosine triphosphate (AT). This energy source is stored in only small amounts within muscles, so the body must continually reproduce it for continued muscular effort. AT is produced via three energy pathways: the phosphate energy system, which uses phosphocreatine to create new AT supplies without oxygen the anaerobic glycolysis energy system, which uses glycogen but no oxygen the aerobic energy system, which uses primarily glycogen and fats (and protein under extreme conditions) to create AT. The phosphate energy system can create AT 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 replenish. The anaerobic glycolysis system takes longer to create AT. It is the major contributor to high-level exertions of seconds, but creates lactic acid 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 60 seconds into a sustained sporting performance. It relies on an efficient circulo-respiratory system. The aerobic creation of AT 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 285: adenosine triphosphate (AT) adipose tissue aerobic glycolysis anaerobic glycolysis carbohydrate (CHO) energy substrates fat glucose glycogen lactate threshold lactic acid (LA) mitochondrion mmol/l of LA OBLA phosphate energy system phosphocreatine (C) protein 2. In class, discuss the following sports or individual events and predict, using pie charts, the relative importance of each of the three energy systems in the successful completion of the activity. Assume they are being performed by elite adult sportspeople: (a) netball (b) cricket (c) Australian Football (d) high jump (e) gymnastics floor routine (f) rowing 2000 m race (g) 400 m run (h) 25 m swim. 226 LIVE IT U 1

20 3. Explain the differences between OBLA and the lactate threshold. 4. What would be the recovery times between one elite performance of the following efforts and a repeat effort? (a) a long jump in athletics (b) a clean-and-jerk lift in a weight-lifting competition (c) an 800 m race in athletics (d) a 100 m race in swimming (e) an Olympic distance triathlon (f) a 100 m athletic heat and the semi final (g) a netball game 5. How does the body deal with the high lactic acid levels created by a high level sub-maximal effort? Useful websites Aerobic energy system Energy systems, aerobic and anaerobic Lactate physiology and sports training Body systems The lactate threshold Major muscle groups and microscopic structure Muscle biochemistry Muscle physiology homepage Muscles Nismat exercise physiology corner: muscle physiology primer CHATER REVISION CHATER 7 ENERGY SYSTEMS AND HYSICAL ACTIVITY 227