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Copyright COMMONWEALTH OF AUSTRALIA Copyright Regulation WARNING This material has been reproduced and communicated to you by or on behalf of the University of Sydney pursuant to Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice Muscle Cells and Contraction Muscle Types • Type I - “Red”, “Slow” – Contracts relatively slowly – Many mitochondria – Good blood supply • Type IIb - “White”, Fast” – Contracts relatively rapidly – Few mitochondria – Poor blood supply – Packed full of contractile filaments Gentle exercise • Type I muscles recruited – good blood supply, heaps of mitochondria • Krebs cycle increases – Acetyl CoA usage increases – Catabolic pathways activated • Most readily available fuel is glucose – Glucose transporters move to cell surface Consequences of Glucose Usage • Muscle glucose uptake leads to a decrease in blood glucose concentration • Need to keep blood glucose constant! – Small change in blood glucose causes... insulin glucagon Effects of Low Insulin and High Glucagon – Stimulation of glycogen breakdown in liver – Stimulation of fat breakdown in white adipose tissue LIVER WAT GLYCOGEN FAT glucose fatty acids fatty acids glucose Glucose Recycling • Glucose stores (glycogen) are limited – Cannot convert fatty acids into glucose • GLUCOSE CONSERVATION AND RECYCLING – Fatty acids substitute for glucose as a fuel – Fatty acids prevent glucose from being wastefully oxidised Fatty Acid and Glucose Oxidation glucose GLYCOLYSIS pyruvate fatty acids FATTY ACID OXIDATION acetyl CoA CO 2 Fatty Acid Oxidation inhibits Glucose Oxidation glucose to liver GLYCOLYSIS pyruvate inhibits fatty acids FATTY ACID OXIDATION acetyl CoA CO 2 lactate Summary of Gentle Exercise – Initially, glucose is used – Then fatty acids take over and glucose is recycled LIVER GLYCOGEN lactate MUSCLE glucose WAT lactate FAT glucose CO2 fatty acids fatty acids CO2 Moderate Exercise • As the pace increases, the rate of fatty acid utilisation increases, but.... – The enzymes that catalyse fatty acid oxidation soon reach their maximum capacity – During running, fatty acid oxidation alone is not sufficient to maintain ATP production – Inhibition on glucose oxidation is removed • Glucose oxidation occurs! • Less glucose recycling • Liver glycogen stores depleted faster Summary of Moderate Exercise LIVER GLYCOGEN lactate MUSCLE glucose WAT lactate FAT glucose fatty acids fatty acids CO2 Strenuous Exercise – As the intensity of the exercise increases further, muscle glycogen is broken down. LIVER GLYCOGEN lactate glucose WAT MUSCLE GLYCOGEN FAT glucose fatty acids fatty acids CO2 Glycogen Depletion during a Marathon Race Glycogen (mg/g) 100 75 slower 50 25 faster 0 0.0 0.5 1.0 1.5 2.0 Time (hours) 2.5 Why Glycogen is Important • When glycogen has run out, only fatty acid oxidation can be used for ATP generation • Power output is lower when using only fatty acids • “Hitting the Wall” • Cannot sprint if there’s no glycogen Strategies • Start the event with more glycogen than your competitors • Spare the glycogen by making more use of fatty acids • Use fatty acids sooner so less glycogen is used in the early stages Glycogen Supercompensation – After extensive depletion, glycogen resynthesis overshoots. 100 75 50 pre-exercise level 25 0 0 1 2 3 Time (days) 4 5 Glycogen Loading - Classical 100 – Interrupts training! – Potentially dangerous – Uncomfortable – Character building! 75 50 HiFAT HiCHO 25 0 0 1 2 3 Time (days) 4 5 Glycogen Loading - Tapered • Fits well into normal training • No dangerous full glycogen depletion. 100 75 50 always High Carbohydrate 25 0 0 1 2 3 Time (days) 4 5 Glycogen Sparing • Increase the use of fatty acids – Carnitine helps fatty acids enter mitochondria – Training increases the activity of fatty acid oxidation enzymes • Start fatty acid release from White Adipose Tissue early – Strong cup of coffee! – NOT glucose drinks BEFORE an event insulin glucagon = inhibition of fatty acid release Fitness • Better cardiovascular system • Increased vascularisation of muscles – better oxygen supply – better fuel supply (especially fatty acids) • More mitochondria – Higher capacity to burn fatty acids • Conversion of Type IIb to Type I? Sprinting • Uses Type IIb muscles – Poor blood supply – Packed full of contractile filaments – Few mitochondria – VERY rapid consumption of ATP • Fuel selection problem – Fatty acids? » oxygen supply, mitochondria – Blood Glucose? » transporter recruitment, blood supply Anaerobic Glycogen Utilisation GLYCOGEN GLYCOLYSIS ADP ATP pyruvate acetyl CoA lactate to blood stream • Inefficient and incomplete • High turnover • Accumulation of lactate • Takes time to stimulate glycogen breakdown Buying time with Creatine Phosphate creatine phosphate + ADP ATP + creatine • Less than 5 seconds supply of creatine phosphate – Enough to get glycogen mobilisation going • Adrenaline stimulates massive glycogen breakdown. Fatigue • Role of lactate?? • Acidity interferes with many processes – Enzymes involved in glycolysis – Contractile process – Calcium movements • All very controversial! – But one things for sure: very low pH and running out of glycogen are definitely bad news – OK, so that was TWO things… Fatigue 2 • Use pH buffers? – Bicarbonate widely used – Certainly works but check with doctor first! • Does glycogen ever run out in a sprint? – Not in short events (100 m) – Important in longer events and multi-heat competitions Does Glycogen run out during Sprinting? 100 • Have to ensure adequate glycogen resynthesis between races • Rapidly absorbed carbohydrate 75 50 25 depleted 0 0 1 2 3 Time (hours) 4 5 Sprint Training • Increased power output – Increased cell size – More contractile filaments – STEROIDS! • Co-ordination • Conversion of Type I to Type IIb? • Adequate glycogen stores Lessons • Muscle Contraction – Muscle Types • Getting energy from fat and carbohydrate – No work, no energy consumption! – Increase work, increased oxidation of fuel • Fuel mix during.... – Walking, Jogging, Running and Sprinting • Training effects How the Fuel Mix Changes LIGHT INTENSE Fatty acids CO2 Fatty acids CO2 Fatty acids CO2 Glucose CO2 Glycogen CO2 Glycogen lactate MODERATE Fatty acids CO2 Glucose CO2 Fatty acids CO2 Glucose CO2 SPRINTING Creatine P creatine Glycogen lactate Take Home Message! • Glycogen is an important fuel to all athletes – Using fatty acids quickly and copiously reduces the use of valuable glycogen • Carbohydrate intake has to be high to allow adequate glycogen synthesis