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1 TOPIC 1: Energy Sources for Physical Performance TOPIC 1: ENERGY SOURCES FOR PHYSICAL PERFORMANCE 1.1 Sources of Nutrients: Carbohydrates, Fats, and Proteins 1.2 Chemical Breakdown of Nutrients: Glucose, Glycogen, Free Fatty Acids 1.3 Aerobic & Anaerobic Energy: ATP-CP, Lactic Acid & Oxygen Systems 1.4 Contribution of Energy Systems for Specific Activities 1.5 Acute Responses to Exercise: Responses in the Circulatory, Respiratory, and Muscular Systems to Provide Energy 2 TOPIC 1: Energy Sources for Physical Performance 1.1 Sources of Nutrients: Carbohydrates, Fats, and Proteins Carbohydrates: After carbohydrates are eaten, they are broken down into the digestive tract and absorbed into the blood as simple sugars (with the glucose molecule being the most common sugar). This absorption occurs in the small intestine because it is the easiest point for the blood to pick up the glucose molecules. Once a glucose molecule enters the blood, it either travels around the blood in the form of glucose or it is stored as glycogen in the muscles. Once muscle stores are full, excess glucose is transported to the liver where is can be stored as glycogen. Glycogen stored in the liver can be converted back to glucose to maintain blood glucose levels, or it may be transported (via the blood) to various muscles as required. Blood glucose (with glycogen) is a major fuel for intense exercise. Two-thirds of the glucose that is stored as glycogen is found in the muscles. This enables the muscles to have the glucose stored “on-site” and ready to be used. Glycogen is the fuel primarily used for high intensity activity. If muscle and liver glycogen stores are full, excess glucose is converted into triglyceride (fat) and stored in then body as adipose tissue (fat cells). Fats: Fats are a major food source for prolonged moderate exercise. They also provide two-thirds of the body’s fuel requirements when at rest. The majority of fat is digested in the small intestine where, under a process called hydrolysis, it is broken up into smaller molecules called monoglycerrides (fatty acids and glycerol). Once absorbed by the intestine, the fatty acids and glycerol combine to form triglycerides – three fatty acid molecules added to one molecule of glycerol. Triglycerides can be stored either in skeletal muscles or adipose tissue (fat cells that provides heat or insulation). Where necessary they will release the fatty acids to the transported by the blood to the working muscles. Protein: Protein only minimally contributes to the production of energy. Only in extreme circumstances (such as starvation or ultra marathon events) when the body has severely depleted its supplies of carbohydrates and fats, protein becomes a viable source of energy. Amino acids found in protein rich foods are the building blocks of the human body and are used for muscle growth and repair. The Body’s Storage of Food Fuel: Food Source Carbohydrate Fat Protein Stored as Site 3 TOPIC 1: Energy Sources for Physical Performance Approximate Fuel and Energy Stores in the Body (Assuming Subject Mass 65kg with 15% Body Fat) The amount of energy stored in the two main nutrient fuels is as follows: Fats (1g) = 37kj (9 cal) Carbohydrates (1g) = 17kj (4 cal) Nutrient Amount stored (g) 1. Carbohydrate Blood glucose Muscle glycogen Liver glycogen 15g 250g 110g Total Carbohydrate 375g 2. Fat Adipose tissue Intramuscular 7800g 160g Total fat 7960g Calculate the ‘energy stored’ in the table above. Energy stored (kj) 4 TOPIC 1: Energy Sources for Physical Performance 1.2 Chemical Breakdown of Nutrients: Glucose, Glycogen, Free Fatty Acids The energy stored in foods is not used directly by the body for biological work. Instead this energy is released to rebuild a chemical compound called adenosine triphosphate (ATP). ATP is the ‘energy currency’ of the human body. ATP is an energy rich molecule that consists of an adenosine molecule and three phosphate molecules chemically joined together. The breaking away of one of the ‘high energy’ phosphate bonds form adenosine diphosphate (ADP) and releases the energy required for all forms of biological work. This process is reversible, meaning ADP + P can be resynthesised to reform ATP, but it requires energy. Carbohydrates (Glucose and Glycogen) Carbohydrates require considerably less ‘work’ (less oxygen) to breakdown, glycogen usage tends to be dominate with intense exercise. For this reason, carbohydrates are considered the body’s primary fuel. For a marathon runner, the preferred fuel is still glycogen, but the body’s stores of carbohydrate are limited. If the athlete runs out of glycogen the body must utilise fatty acids as the major fuel source. Fats (Free Fatty Acids) Fats are larger molecules requiring more ‘work’ (more oxygen) to breakdown. It is harder work for an athlete who is trying to breakdown fat and as a result their performance will decline. They will find it difficult to concentrate and may appear disorientated; this term is ‘hitting the wall’. Therefore fats tend to be more dominant at low intensity when oxygen delivery is not a limiting factor. Resynthesis of ATP Carbohydrates and fats are the main nutrient fuels used to supply the energy needed to the resynthesise of ATP, but the relative contribution of carbohydrates and fat as a fuel will depend to a large degree on the exercise duration and intensity. Fats can only be broken down to resynthesis ATP in a process requiring oxygen called aerobic lipolysis. Carbohydrates can be broken down aerobically in a process called aerobic glycolysis, but they may also be broken down without oxygen (anaerobically) in a process called anaerobic glycolysis. 5 TOPIC 1: Energy Sources for Physical Performance 1.3 Aerobic and Anaerobic Energy: ATP-CP System, Lactic Acid System, Aerobic System. Adenosine Triphosphate (ATP) The energy required by the body to sustain life and for the contraction of muscles to produce movement is derived from the food we eat. When food is digested, it is broken down into CHEMICAL COMPOUNDS including carbohydrates, fats, and proteins. These chemicals compounds contain energy. FOOD Carbohydrates Fats Proteins The energy contained in carbohydrates, fats, and protein cannot be used directly by the body. Instead it is used to form a chemical compound called ADENOSINE TRIPHOSPHATE (ATP). ATP: ADENOSINE P P P ATP is stored in small amounts in all muscle cells. It is the energy released, during the breakdown of ATP into ADENOSINE DIPHOSPHATE (ADP) and the third PHOSPHATE, which represents the immediate source of energy that can be used by the muscle cells to perform work. Breakdown of ATP into ADP + P: ADENOSINE P P P ENERGY RELEASED ATP → ADP + P Sources of ATP: ATP can be stored in the muscles in only small amounts. Once this store has been used up, the body must supply the muscle with more ATP for it to continue working. The supply of ATP is limited by the intensity and duration of the physical activity. PRIMARY SOURCE OF ATP: carbohydrates, which are broken down to glucose and glycogen. SECONDARY SOURCE OF ATP: fats, which are broken down into free fatty acids. EXTREME SOURCE OF ATP: proteins, only under extreme conditions. 6 TOPIC 1: Energy Sources for Physical Performance Sources of Energy to Perform Work IS DIGESTED INTO USED TO FORM CHEMICAL COMPOUND ATP CHEMICAL ENERGY BREAKING OF PHOSPHATE BONDS GIVES ENERGY BREAKING OF PHOSPHATE BONDS GIVES ENERGY ADENOSINE P P P ENERGY RELEASED → ENERGY RELEASED IS USED BY MUSCLES TO WORK ENERGY RELEASED IS USED BY MUSCLES TO WORK 7 TOPIC 1: Energy Sources for Physical Performance The ATP-CP System Small amounts of ATP are stored in the muscles. Energy is released when the chemical bonds (phosphate bonds) of the ATP are broken. Adenosine triphosphate has 3 phosphates. One of these breaks away to leave adenosine diphosphate (ADP) and a single phosphate: ATP → ADP + P When exercise begins, ATP stored in muscles is used to release energy for muscular contraction. However, the stores of ATP are limited, and if exercise continues, the ADP and Phosphate must be recombined to produce more ATP. The body has the ability to remake ATP as quickly as it is broken down by using another Phosphate fuel called creatine phosphate (CP) which is also stored in muscles. Creatine phosphate is broken down into creatine and phosphate, releasing energy which is used to rejoin ADP and phosphate to form ATP. Unfortunately, stores of CP in the muscles are also limited, so the energy formed via this system only lasts for about 10 seconds of high intensity exercise, and is not replenished until approximately 2-3 minutes of rest. For this reason, the ATP-CP system is the predominate energy system for producing ATP for sudden bursts of activity that takes less than 10 seconds such as a high jump, a tennis serve, a short sprint, or a javelin throw. The ATP-CP system relies on stores that are readily available in the muscles and therefore energy can be released the moment it is required. The body does not have to go through a complex set of reactions. It is the most immediate source of ATP, providing energy for muscular contraction at the commencement of an activity. The ATP-CP system is also known as the ATP-PC system, Alactacid system and Phosphagen system. The ATP-CP System ATP STORES IN MUSCLE ATP RECOMBINED ADP + P → ATP ATP → ADP + P ENERGY RELEASED ENERGY RELEASE D MUSCLE CONTRACTION CP → C + P CP STORES IN MUSCLES TOPIC 1: Energy Sources for Physical Performance The Lactic Acid System If exercise continues beyond 10 seconds, the stores of ATP in muscles are exhausted. The body must therefore resort to an alternative source of ATP, and the second of the energy systems in the anaerobic pathway takes over. This is the Lactic Acid system. The Lactic Aacid system uses carbohydrates from the food eaten, as the fuel for manufacturing ATP. Carbohydrates are converted into glucose which is transported by the blood to the muscles and liver to be stored as glycogen. With the aid of enzymes (proteins which initiate specific chemical reactions), the glycogen is converted into a substance called Lactic Acid. During this reaction, energy is released, and this energy is used to recombine the ADP and Phosphate to ATP. Only 2 ATP molecules are produces for each glucose molecule. Unfortunately, like the ATP-CP system, the Lactic Acid system is functional only for a limited time. The Lactic Acid produced by the chemical reaction is toxic in large amounts. As it begins to build up in the muscles, discomfort and fatigue set in. An often quoted example of this is the feeling of heavy legs in the home straight of a 400m sprint. This is a symptom of lactic acid build-up. The Lactic Acid system therefore provides ATP for high intensity activities lasting between 30 seconds to 2 minutes, such as a gymnastics floor routine, a 400m sprint, or a 200m swim. If exercise is to be maintained beyond this time, its intensity must be reduced as the rapid production of ATP through the Lactic Acid system cannot be sustained for very long, and the accumulation of lactic acid in the muscles will prevent continued efficient muscle contraction at high intensity. The Lactic Acid system is also known as Anaerobic glycolysis (the breakdown of glucose without oxygen) and Lactacid system . The Lactic Acid System CARBOHYRDATE ATP RECOMBINED GLUCOGEN STORED IN MUSCLE ADP + P → ATP ACTION OF ENZYMES ENERGY RELEASED BY PRODUCT 8 LACTIC ACID 9 TOPIC 1: Energy Sources for Physical Performance The Aerobic Energy System After 2 to 3 minutes of exercise, respiratory rate, tidal volume, heart rate, stroke volume, cardiac output and arteriovenous oxygen difference all increase sufficiently to supply the working muscles with enough oxygen to produce ATP aerobically. Aerobic production of ATP can involve the breakdown of carbohydrate, fat or protein to release large amounts of ATP (32 molecules of ATP for each molecule of glucose). The by-products of the reaction are carbon dioxide and water. Carbohydrates can provide sufficient fuel for about 2 or 3 hours of exercise, after which time the body needs to look for alternative sources of fuel. Exercise can be continued by using the reserve fuel (fat). To produce energy from fat, requires far more oxygen than to produce the same amount of energy from carbohydrate. For the same rate of energy production is to be maintained, the cardio-respiratory system will be overtaxed in delivering the additional oxygen required for the breakdown of fat. As a result the athlete will become breathless, fatigued and will eventually have to reduce intensity of exercise or stop. Protein is used as a fuel for ATP production only in extreme cases of prolonged physical work. Ultra marathons of 4 – 5 days duration would rely on protein to provide ATP in the final stages of the event. The Aerobic system is also known as the Oxygen system, Aerobic glycolysis (the breakdown of carbohydrate in the presence of oxygen) and Aerobic lipolysis (the breakdown of fat in the presence of oxygen). The Aerobic Energy System GLYCOGEN FATS PROTEIN WITH SUFFICIENT OXYGEN ENERGY RELEASED USED TO RECOMBINED ATP MOLECULE ADP + P → ATP All Systems Go Again ATP BY PRODUCT CARBON DIOXIDE BREATHED OUT WATER PERSPIRATION 10 TOPIC 1: Energy Sources for Physical Performance Watch ‘All Systems Go Again’ on Click View and answer the following questions: ATP-CP System 1. What does the term anaerobic mean? 2. What is the role of Creatine Phosphate? 3. State a time span for this particular energy system. Give 4 examples of sports where the energy for this activity is predominantly provided by this reaction. Lactic Acid System 4. What do you understand by the term ‘glycogen’? 5. State a time span for this particular energy system. Give 4 examples of sports where the energy for this activity is predominantly provided by this reaction. Aerobic Energy System 6. Why does your heart rate and breathing rate increase whilst you are exercising aerobically? 7. What is the downside of using fat as the fuel for aerobic glycolysis? 11 TOPIC 1: Energy Sources for Physical Performance 8. State a time span for this particular energy system. Give 4 examples of sports where the energy for this activity is predominantly provided by this reaction. Interplay of energy systems 9. Using relevant examples, describe why just one energy system is not solely used in most team games? 10. Define the term VO2 max and state the units it is measured in. 11. What are the average levels for VO2 max for an average sedentary male and an elite endurance athlete? 12 TOPIC 1: Energy Sources for Physical Performance Pathways for Energy Production ANAEROBIC PATHWAY ATP-CP ENERGY SYSTEM AEROBIC PATHWAY LACTIC ACID ENERGY SYSTEM AEROBIC ENERGY SYSTEM Summary of the 3 Energy Systems: Characteristic 1. Oxygen requirements for energy source reaction 2. Energy source for ATP production ATP-CP System Lactic Acid System Aerobic System Anaerobic – no oxygen required Anaerobic – no oxygen required Aerobic – oxygen required in the reaction Chemical fuel - Creatine Phosphate (CP) Food source Carbohydrates Glycogen Food source Carbohydrates Fat Protein 3. Duration of energy system 4. Intensity 5. Recovery time until repeat effort 6. Factors when operating maximally 7. Specific sporting examples 8. Everyday activity examples CP replenishments: 3-5 minutes 50% in first 30 secs Rest recovery best Depletion of ATP and CP stores Removal of lactic acids to rest levels. With active recovery: - 50% removal in 15 mins - 95% removal in 30 mins With passive recovery: - 50% removal in 30 mins - 95% removal in 60 mins Lactic acid accumulation Restoration of body glycogen stores: After competition of more that 1 hr: 2448hrs After hard interval training: 6-24hrs By product of water and carbon dioxide 13 TOPIC 1: Energy Sources for Physical Performance Positives & Negatives of Energy Systems The ATP-CP System Positives Negatives The Lactic Acid System Positives Negatives The Aerobic System Positives Negatives 14 TOPIC 1: Energy Sources for Physical Performance Maximum Oxygen Consumption (VO2 Max) VO2 Max = the volume of oxygen consumed by the body for energy production. It is measured in litres of oxygen consumed per minute (L/min). If an athlete were to slowly increase exercise intensity, there would be a corresponding increase in oxygen consumption until they reached maximum oxygen consumption (VO2 Max) – the region where oxygen uptake peaks despite further increases in exercise intensity (refer to the following diagram). Because larger people tend to consume more oxygen than smaller people (purely because of their larger size), VO2 Max is usually expressed as a relative VO2 Max in millilitres of oxygen consumed per kilogram of body weight per minute (ml/kg/min). This allows for the comparison of different-sized individuals. For example, in the following diagram the athlete’s peak VO2 Max value was 3.6 litres per minute. If the athlete undergoing this test had a mass of 68kg, then their average relative oxygen consumption would be calculated as follows: 3.6L/min x 1000 = 3600ml 3600/68kg = 52.9ml/kg/min The VO2 Max is an important indicator in determining a person’s capacity for the aerobic resynthesis of ATP, with elite endurance athletes having higher values than other sports performers. Untrained individuals would have a VO2 Max of approximately 40ml/kg/min, while values exceeding 70ml/kg/min or beyond are only achieved by superbly conditioned endurance athletes. 15 TOPIC 1: Energy Sources for Physical Performance Anaerobic Threshold (AT) Anaerobic Threshold (AT) is the maximum intensity of steady state exercise (% VO2 max) that a person can sustain without a rapid increase in the accumulation of lactic acid. It should be noted that exercise intensities approaching VO2 max can only be achieved through the dominant use of the lactic acid system with subsequent formation and accumulation of lactic acid. Generally speaking, the most common reference point for anaerobic threshold is thought to be when blood lactate levels exceed 4 ml per litre of blood. Because there is no actual threshold point where aerobic processes simply ‘stop’ and anaerobic processes simply ‘begin’, anaerobic threshold is more correctly referred to as the Onset of Blood Lactic-acid Accumulation (OBLA). A person’s anaerobic threshold, or OBLA, has a large impact on the athletic performance. It determines the maximum exercise intensity they can maintain for an extended period of time without the fatiguing effects of lactic acid accumulation. Generally speaking, individuals with higher AT or OBLA values (expressed as a % of their VO2 max) are the better endurance performers. Through training, VO2 max and anaerobic threshold can be improved. 16 TOPIC 1: Energy Sources for Physical Performance 1.3 Aerobic and Anaerobic Energy: ATP-CP System, Lactic Acid System, Aerobic System. Oxygen Deficit Oxygen Deficit = the period of time at the start of exercise where the level of oxygen consumption is below the necessary level to supply ATP aerobically. Because it takes 2-3 minutes to increase the O2 supply sufficiently, the two anaerobic systems must provide the required ATP during this time, thus creating an oxygen deficit. 17 TOPIC 1: Energy Sources for Physical Performance Oxygen Debt or Excess Post-Exercise Oxygen Consumption (EPOC) Oxygen Debt or EPOC = the period of time after exercise where O2 consumption will remain elevated to allow the body to slowly return to pre-exercise levels. During this stage, the heart and lungs continue to deliver O2 to the body to rebuild energy supplies. This is usually seen at the end of a race where a runner will pant vigorously. There 2 components of EPOC: ALACTACID COMPONENT (fast) = the O2 consumed in early recovery to replenish ATP-CP stores and to resupply oxygen bound to myoglobin. This process is accomplished very quickly; 30 seconds for 50% replenishment and 3 minutes for 100%. LACTACID COMPONENT (slow) = the extra O2 is consumed and used to breakdown and remove lactic acid that has accumulated, resynthesise glycogen, restore body temperature and normal breathing. This process can take 1-2 hours to be completely repaid, however an active recovery can speed up the process. Continuous activity post-exercise (at about 55-60% VO2 max) will speed up the removal of lactic acid. o It prevents blood pooling in the extremities o It allows the skeletal muscles to oxidise some of the lactic acid for energy (70%) o An elevated heart rate keeps blood circulation to the liver high, assisting with the conversion of lactic acid back to glycogen. 18 TOPIC 1: Energy Sources for Physical Performance 1.4 Contribution of Energy Systems for Specific Activities Interplay of Energy Systems At any one time, all three energy systems will be functioning. It is the intensity of exercise (how quickly ATP is required) and the duration of exercise (how much ATP is required) that will determine which energy system(s) will be dominant in any activity. As exercise intensity increases there is a greater reliance on the more powerful anaerobic systems and as the duration of exercise increases (to around 2 minutes or more), the dominant energy system will become more aerobic in nature. The above diagram shows how the three systems vary in their percentage contribution to energy/ATP production depending on the duration of the activity. During a football or netball match, what would the energy system contribution be for key centre players who may not be working maximally for extended periods of time? As soon as the players start moving, the ATP−PC system starts providing energy. This system reaches its peak within the first five seconds, at which point the other anaerobic system – the lactic acid system – becomes the major supplier of ATP. The ATP−PC system continues to supply energy, but is limited by the amount of PC and will be totally drained after 12 to 15 seconds. As the players keep moving on the field or court, the aerobic system increases its contribution and takes over from the lactic acid system as the major energy system contributor at one to two minutes into play. Oxygen can be made available to working muscles at a much quicker rate than previously thought. Explosive energy for short sprints and rapid movements is provided by the lactic acid system as the ATP−PC system has not had an opportunity to recharge. However, ATP is provided by the aerobic system in large quantities even during high-intensity activities. 19 TOPIC 1: Energy Sources for Physical Performance Example 1 In a 6 second dash to escape from a vicious dog, the subject running at high speed will utilise predominantly the ATP-CP system. Yet, the other two systems will contribute something even if extremely little. Therefore, the ATP-CP energy system will be the dominant energy system. Note that if the subject is still running at a high speed after 60 seconds, the contribution of the ATP-CP energy system has drastically fallen, being replaced as the dominant energy system by both the Lactic Acid system and Aerobic system. Example 2 In a 200m sprint at the elite level, the intensity suggests the anaerobic energy systems as the dominate source of energy. The duration of the event points more to the lactic acid system because after 10 seconds the majority of the CP stores have been exhausted. 20 TOPIC 1: Energy Sources for Physical Performance 1.5 Acute Responses to Exercise: Responses in the Circulatory, Respiratory and Muscular Systems to Provide Energy Complete the following task using your text books: 1. Define the following terms: a. Acute response b. Chronic response 2. For each of the terms below: a. Define the term. b. State how it changes. c. State why it changes. Heart Rate Stroke Volume Cardiac Output A-v O2 Difference Blood Pressure Tidal Volume Ventilation Oxygen Uptake Blood Volume Complete the following Laboratory Activity: Perform the following activities, taking your pulse for 15 seconds immediately after you complete each activity. a. b. c. d. Walking for 2 minutes Running for 2 minutes Set-ups on a bench for 2 minutes Bent-knee sit ups for 2 minutes Record and graph results. Multiply by 4 to determine your heartbeats per minute. Identify which exercise caused the highest heart rate. Discuss the relationship between your heart rate and the intensity of your activity. Explain why you should not measure your pulse rate with you thumb. Then: