VCE Physical Education - Unit 3 Chapter 6 Muscular Fatigue Mechanisms Text Sources 1.Nelson Physical Education VCE Units 3&4: 4 th Edition – Malpeli, Horton,

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VCE Physical Education - Unit 3 Chapter 6 Muscular Fatigue Mechanisms Text Sources 1.Nelson Physical Education VCE Units 3&4: 4 th Edition Malpeli, Horton, Davey and Telford 2006. 2. Live It Up 2: 2 nd Edition Smyth, Brown, Judge, McCallum and Pritchard 2006. Slide 2 What is Fatigue? Muscular Fatigue Mechanisms Slide 3 VCE Physical Education - Unit 3 What is Fatigue? Fatigue occurs when the body is unable to function at its optimal level. The muscles are unable to exert maximal force levels as a result of exercise. Fatigue occurs through everyday physical activity. Exercise increases the physiological effects of fatigue. Our response to fatigue depends on; The type, intensity and duration of the activity The fitness level and mental state of the performer. The muscle fibre being usedmuscle fibre Types of muscular contraction occurringmuscular contraction The amount of metabolic by products being produced The athletes hydration levels Slide 4 VCE Physical Education - Unit 3 Muscle Fibre Type and Fatigue Fast Twitch Fibres - Fast reaction time which relies on PC stores. Unfortunately these stores deplete quickly. Fast twitch also have a reduced oxygen supply in comparison to the aerobic slow twitch fibres. Slow Twitch High stores of glycogen and triglycerides helps produce energy for endurance activities. Eventually fuel reserves are depleted or the neuromuscular process breaks down. See fig 6.2 and 6.3 p.132-133 Slide 5 VCE Physical Education - Unit 3 Slide 6 Muscular Contraction Types Muscle Contraction Muscular ActionExamples IsotonicMuscle length changes throughout range of movement. There are two types of isotonic contractions; 1.Concentric Shortening of muscle while force is developed 2.Eccentric Lengthening of muscle while force is developed Push ups Sit ups Throwing Kicking Most sports IsometricNo change in muscle length while force is developed. However this training method causes an increase in blood pressure. Pushing against wall Holding a bat IsokineticHigh-speed contraction through full range of motion. Needs specialist training equipment Slide 7 VCE Physical Education - Unit 3 Types of fatigue 1.Local Fatigue in specific muscle group Eg. Biceps during bicep curls 2.General Fatigue in all muscles groups Eg. After completing full weights session 3.Chronic Unhealthy level of fatigue, caused by breakdown of bodys defences. Eg. Chronic fatigue syndrome Slide 8 VCE Physical Education - Unit 3 Levels of Fatigue Slide 9 Causes of Fatigue Muscular Fatigue Mechanisms Slide 10 VCE Physical Education - Unit 3 Causes of Fatigue A number of processes cause muscular fatigue including; Energy Systems used Depleted fuel stores (Glycogen / PC and other phosphate compounds)Depleted fuel stores Metabolic by-products Reduced ability to extract energy Increased body temperature Dehydration Changes in blood flow Slide 11 Fuel stores (PC and glycogen) Metabolic By-products (LA, H +, P i, Creatine) Energy pathways Causes of Fatigue p.134 Hydration levels Blood flow & redistribution Body Temperature Slide 12 Depletion of Fuels Muscular Fatigue Mechanisms Slide 13 VCE Physical Education - Unit 3 Fuel Depletion Most commonly exhausted energy stores are PC and glycogen. Stores of glycogen in the muscle and liver can fuel continuous exercise for over 90 mins. Muscle glycogen is generally the first fuel source used during aerobic exercise; then liver glycogen and eventually blood-borne and stored fat. Fat conversion to energy is far less efficient than that for glycogen, resulting in a reduced intensity. As energy stores are continually depleted, fatigue occurs and therefore the quality of performance decreases Slide 14 VCE Physical Education - Unit 3 Slide 15 Aerobic Pathway & Fatigue Aerobic Exercise Less than 20 minutes; No major fatigue and carbos and fats used as energy (Very little lactic acid). Extended activities (Greater than an hour); Fats used as fuel therefore body must slow down (More oxygen required). Fatigue caused by depleted fuel stores, dehydration, increased body temp, physical and mental stress. Low Energy Stores Athletes should follow strict diets when preparing for events so that fatigue is minimised or delayed. Slide 16 VCE Physical Education - Unit 3 Anaerobic Pathway & Fatigue Anaerobic Exercise Energy supplied by Phosphate Creatine (1-15 sec) and anaerobic glycolysis (15sec-2min). Oxygen deficit occurs. Fatigue caused by lactic acid accumulation, which inhibits muscular contractions (Prevents calcium ion flow to myosin filament). Lactic acid also prevents enzymes breaking down glucose stores Slide 17 VCE Physical Education - Unit 3 Slide 18 Metabolic By-Products Muscular Fatigue Mechanisms Slide 19 VCE Physical Education - Unit 3 Metabolic by-products Metabolic by-products are compounds made as a result of chemical reactions within the body. They are the left-overs as such. When making ATP using phosphocreatine, the by-product is creatine: ADP + PC ATP + creatine By-products can prove harmful to the body by causing it to function in a less efficient way, such as through the effect of lactate and hydrogen ions during physical activity. These by-products effect; Contraction of myosin, disruption to the work of enzymes, the neuromuscular junction, ionic concentrations. Summary See fig 6.7 p.136 p.137 Slide 20 VCE Physical Education - Unit 3 By-products - Accumulation of LA Lactic acid Produced as a result of pyruvic acid reacting in the absence of oxygen. As the rate of anaerobic glycolysis increases, lactic acid accumulates. It effects the ability of energy extracting enzymes to work effectively. It also lowers the bloods pH levels. Lactic acid eventually reaches maximum levels within both the muscle fibres and in the blood (Lactate threshold). Fatigue results as the accumulated lactic acid inhibits muscular contractions. Slide 21 VCE Physical Education - Unit 3 How LA affects muscular contractions Inhibiting the secretion of calcium ions that enable the coupling of the actin and myosin protein filaments. Protein filaments cannot attach to each other. The sliding of filaments is not possible. Inhibiting the action of the glycolytic enzymes resulting in glucose not being broken down. Slide 22 VCE Physical Education - Unit 3 By-Product 2 - Accumulation of H + ions Another by-product of anaerobic glycolysis. Accumulation of H + ions within the working muscle and blood plasma results in the levels of pH of the cell decreasing to an extent where muscle contraction is no longer possible and fatigue occurs. The low pH created by the H + ions causes the glycolytic enzymes to become inoperative. Without the glycolytic enzymes, the breakdown of glucose cannot take place. Inorganic phosphate (P i ) can also have a similar fatiguing effect on the body. Slide 23 The Redistribution of Blood Flow Muscular Fatigue Mechanisms Slide 24 VCE Physical Education - Unit 3 Redistribution of Blood Flow During exercise; Increased demand for oxygen Increased waste products Increased blood volume to working muscles Increased cardiac output Less blood flow to vital organs and more to the working muscles This can cause an increase in core body temperature. The body therefore needs to monitor its balance between cooling and muscle supply (Thermoregulation) Body Temperature Increase Due to blood being brought to the surface (vasodilation of veins) of the skin (cooling mechanism), less blood is supplied to the working muscles. This lessens the ability to produce ATP and lactic may be produced. See fig 6.2 p.138 and 6.8 p.139 p.138 Slide 25 VCE Physical Education - Unit 3 Slide 26 Dehydration Muscular Fatigue Mechanisms Slide 27 VCE Physical Education - Unit 3 Dehydration Sweating causes; A loss of salt, electrolytes and water. This can cause; Impaired coordination, decision making and endurance levels. An impact on the cardiovascular system A rise in body temperature Levels of dehydration are affected by; Duration and intensity of session Environmental conditions and acclimatisation. The individual physiological characteristics Fluid intake Athletes can become dehydrated due to; Not having access to fluids during competition Not tolerating drinking while exercising Inability to match intake with loss of fluids If dehydrated, athletes are more prone to; Cramp, heat stress and heat stroke, poor performances and increase the risk of injury. Slide 28 VCE Physical Education - Unit 3 Dehydration Sweating is the bodys natural process for regulating body temperature during exercise. As an athletes core temperature increases so does the rate of sweat production. Sweat contains electrolytes, salts and water, and dehydration is the loss of this body fluid. Varying rates of sweat, work, fluid intake and individual physiological characteristics all contribute to the level of dehydration that may be experienced. Slide 29 VCE Physical Education - Unit 3 Dehydration Signs of dehydration; Mild to severe thirst Rapid loss in weight (1 kg of weight lost = 1L of sweat lost). Dry lips and tongue, confusion Decreased urine volume Dark urine Increased breathing rate Light headedness nausea and headache Confusion, nausea, headache faster breathing rate than normal, Fluid loss can be prevented by; Drinking water prior, during and after events. Use sports drinks for extended activities Use a fluid replacement routine Avoid being dehydrated before sport Written Report p.140 Case Study p.141 p.141 Slide 30 VCE Physical Education - Unit 3 Dehydration continued Combination of dehydration and electrolyte loss can make the athlete more susceptible to cramp, heat stress and heat stroke. A loss of 2% of body weight (just 1 kg for a 50-kg person) causes an increase in perceived effort and could reduce performance by 10-20 %. Loss exceeding 3-5% of body weight reduces aerobic exercise performance noticeably and impairs reaction time, judgment, concentration, cognitive abilities and decision m


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