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Transcript
Chapter 3, 6 Bioenergetics Measurement of Work, Power, and Energy Expenditure Bioenergetics • Muscle only has limited stores of ATP • Formation of ATP – Phosphocreatine (PC) 磷酸肌酸breakdown – Degradation of glucose and glycogen (glycolysis) – Oxidative formation of ATP • Anaerobic pathways 無氧代謝 – Do not involve O2 – PC breakdown and glycolysis • Aerobic pathways 有氧代謝 – Require O2 – Oxidative phosphorylation Anaerobic ATP Production • ATP-PC system – Immediate source of ATP PC + ADP Creatine kinase ATP + C – Onset of exercise, short-term high-intensity (<5 s) • Glycolysis 醣解作用 – Energy investment phase • Requires 2 ATP – Energy generation phase • Produces ATP, NADH (carrier molecule), and pyruvate 丙酮酸 or lactate 乳酸 The Two Phases of Glycolysis Glycolysis: Energy Investment Phase Glycolysis: Energy Generation Phase Oxidation-Reduction Reactions • Oxidation – Molecule accepts electrons (along with H+) • Reduction – Molecule donates electrons • Nicotinomide adenine dinucleotide (NAD) NAD + 2H+ NADH + H+ • Flavin adenine dinucleotide (FAD) FAD + 2H+ FADH2 Production of Lactic Acid (lactate) • Normally, O2 is available in the mitochondria to accept H+ (and electrons) from NADH produced in glycolysis – In anaerobic pathways, O2 is not available • H+ and electrons from NADH are accepted by pyruvic acid (pyruvate) to form lactic acid Conversion of Pyruvic Acid to Lactic Acid • Recycling of NAD (NADH NAD) • So that glycolysis can continue • LDH: lactate dehydrogenase 乳酸去氫脢 Aerobic ATP Production • Krebs cycle 克氏循環(citric acid cycle, TCA cycle, tricarboxylic acid cycle) – Completes the oxidation of substrates and produces NADH and FADH to enter the electron transport chain – O2 not involved • Electron transport chain – Oxidative phosphorylation – Electrons removed from NADH/FADH are passed along a series of carriers to produce ATP – H+ from NADH/FADH: accepted by O2 to form water The Three Stages of Oxidative Phosphorylation The Krebs Cycle Relationship Between the Metabolism of Proteins, Fats, and Carbohydrates Bioenergetics of fats • Triglycerides 三酸甘油酯 – Glycerol + 3 fatty acids – Fatty acids converted to acetyl-CoA (乙輔酶A) through beta-oxidation – Glycerol can be converted to glycolysis intermediates (phosphoglyceraldehyde) in liver, but only limited in muscle – Glycerol is NOT an important direct muscle energy source during exercise Formation of ATP in the Electron Transport Chain The Chemiosmotic Hypothesis of ATP Formation • Electron transport chain results in pumping of H+ ions across inner mitochondrial membrane – Results in H+ gradient across membrane • Energy released to form ATP as H+ diffuse back across the membrane • O2 accept H+ to form water • O2 is essential in this process The Chemiosmotic Hypothesis of ATP Formation Aerobic ATP Tally Metabolic Process High-Energy Products Glycolysis 2 ATP 2 NADH Pyruvic acid to acetyl-CoA Krebs cycle 2 NADH ATP Subtotal ATP from Oxidative Phosphorylation 2 (if — anaerobic) 6 8 (if aerobic) 14 6 2 GTP 6 NADH 2 FADH — 18 4 Grand Total 16 34 38 38 Efficiency of Oxidative Phosphorylation • Aerobic metabolism of one molecule of glucose – Yields 38 ATP • Aerobic metabolism of one molecule of glycogen – Yields 39 ATP • Overall efficiency of aerobic respiration is 40% – 60% of energy released as heat Control of Bioenergetics • Rate-limiting enzymes – An enzyme that regulates the rate of a metabolic pathway • Levels of ATP and ADP+Pi – High levels of ATP inhibit ATP production – Low levels of ATP and high levels of ADP+Pi stimulate ATP production • Calcium may stimulate aerobic ATP production Action of Rate-Limiting Enzymes Control of Metabolic Pathways Pathway Rate-Limiting Enzyme Stimulators Inhibitors ATP-PC system Creatine kinase ADP ATP Glycolysis Phosphofructokin AMP, ADP, Pi, ase pH Isocitrate ADP, Ca++, dehydrogenase NAD ATP, CP, citrate, pH ATP, NADH Cytochrome Oxidase ATP Krebs cycle Electron transport chain ADP, Pi Interaction Between Aerobic and Anaerobic ATP Production • Energy to perform exercise comes from an interaction between aerobic and anaerobic pathways – 水龍頭 不是電燈開關 • Effect of duration and intensity – Short-term, high-intensity activities • Greater contribution of anaerobic energy systems – Long-term, low to moderate-intensity exercise • Majority of ATP produced from aerobic sources Units of Measure 單位 • Metric system – Used to express mass, length, and volume – Mass: gram (g) – Length: meter (m) – Volume: liter (L) • System International (SI) units – Standardized terms for measurement of: • • • • Energy: joule (J) 能量: 焦耳 Force: Newton (N) 力: 牛頓 Work: joule (J) 做功:焦耳 Power: watt (W) 功率: 瓦特 Work and Power Defined Work 功 作功 Work = force x distance • Lifting a 5 kg weight up a distance of 2 m Work = force x distance Work = 5 kg x 2 m Work = 10 kgm 1 kgm = 9.8 joule 1 joule = 0.24 calorie 卡 (不是 Kcal 大卡, 千卡) Power 功率 Power = work time • Performing 2,000 kgm of work in 60 seconds Power = work time Power = 2,000 kgm 60 s Power = 33.3 kgm•s-1 1 kgm/s = 9.8 watt Measurement of Work and Power • Ergometry: measurement of work output • Ergometer 測功儀: apparatus or device used to measure a specific type of work Measurement of Work and Power • Bench step – Work = body weight (kg) x distance•step-1 x steps•min-1 x minutes – Power = work minutes • Cycle ergometer – Work = resistance (kg) x rev•min-1 x flywheel diameter (m) x minutes – Power = work minutes • Treadmill – Work = body weight (kg) x speed (m•min-1) x grade x minutes – Power = work minutes Determination of Percent Grade on a Treadmill Measurement of Energy Expenditure • Direct calorimetry – Measurement of heat production as an indication of metabolic rate Foodstuff + O2 ATP + Heat Cell work Heat • Indirect calorimetry – Measurement of oxygen consumption as an estimate of resting metabolic rate Foodstuff + O2 Heat + CO2 + H2O Direct calorimetry chamber Ex Nutr c4-energy 30 Indirect calorimetry Closed circuit method Ex Nutr c4-energy 31 Indirect calorimetry Open-Circuit Spirometry Douglas bags for gas analysis Ex Nutr c4-energy 33 Breath-by-breath gas analyzer Ex Nutr c4-energy 34 Ex Nutr c4-energy 35 Estimation of Energy Expenditure • Energy cost of horizontal treadmill walking or running – O2 requirement increases as a linear function of speed • Expression of energy cost in METs – 1 MET = energy cost at rest, metabolic equivalent – 1 MET = 3.5 ml•kg-1•min-1 Linear Relationship Between VO2 and Walking or Running Speed Calculation of Exercise Efficiency • Net efficiency Work output % net efficiency = Energy expended x 100 above rest • Net efficiency of cycle ergometry – 15-27% Upper limits of energy expenditure • Well-trained athletes can expend ~1000 kcal/h for prolonged periods of time • Up to 9000 kcal/d in Tour de France • More than 10,000 kcal/d in extreme longdistance running • Energy requirements can be met by most athletes, if well-planned (e.g. 20% CHO solution during exercise) Ex Nutr c4-energy 39 Ex Nutr c4-energy 40 Ex Nutr c4-energy 41 Factors That Influence Exercise Efficiency • Exercise work rate – Efficiency decreases as work rate increases – Energy expenditure increase out of proportion to the work rate • Speed of movement – There is an optimum speed of movement and any deviation reduces efficiency – Optimum speed at power output – Low speed: inertia, repeated stop and start – High speed: friction • Fiber composition of muscles – Higher efficiency in muscles with greater percentage of slow fibers Net Efficiency During Arm Crank Ergometery Relationship Between Energy Expenditure and Work Rate Force-velocity relationship power output-velocity relationship Effect of Speed of Movement of Net Efficiency Running Economy • Not possible to calculate net efficiency of horizontal running • Running Economy – Oxygen cost of running at given speed – Lower VO2 (ml•kg-1•min-1) indicates better running economy • Gender difference in running economy – No difference at slow speeds – At “race pace” speeds, males may be more economical that females Comparison of Running Economy Between Males and Females Estimate O2 requirement of treadmill running • Horizontal: • VO2 (ml/kg/min) = 0.2 ml/kg/min/m/min x speed (m/min) • Vertical: • VO2 (ml/kg/min) = 0.9 ml/kg/m/min x vertical velocity (m/min) • = 0.9 ml/kg/m/min x speed (m/min) x grade (%) • Total VO2 (ml/kg/min) = horizontal + vertical + rest (3.5 ml/kg/min) Estimate energy consumption according to O2 requirement • ml/kg/min x kg x min • 1 L O2 consumed = 5 kcal Example • • • • • • • • 50 kg, 30 min Speed: 12 km/hr, grade 1% Speed: 200 m/min H: 0.2 x 200 = 40 V: 0.9 x 200 x 0.01 = 1.8 Total: 40 + 1.8 + 3.5 = 45.3 ml/kg/min Total O2: 45.3 x 50 x 30/1000 = ? L O2 Total energy: ? X 5 = Kcal