Exercise Physiology 11th Edition - Chapter 4 PDF

Because learning changes everything. ® EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance 11th Edition Scott K. Powers, Edward T. Howley, and John...

Because learning changes everything. ® EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance 11th Edition Scott K. Powers, Edward T. Howley, and John Quindry Presentation prepared by: Scott K. Powers, Ph.D., Ed.D., Edward T. Howley, Ph.D., and John Quindry, PhD. Copyright ©2021 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.  Because learning changes everything. ® Exercise Metabolism Chapter 4 © McGraw Hill  Lecture Outline Energy Requirements at Rest. Rest-to-Exercise Transitions. Recovery from Exercise: Metabolic Responses. Metabolic Responses to Exercise: Influence of Duration and Intensity. Estimation of Fuel Utilization During Exercise. Factors Governing Fuel Selection. © McGraw Hill 3  Energy requirements at rest Almost 100% of ATP produced by aerobic metabolism. Blood lactate levels are low (5 seconds. Shift to ATP production via glycolysis. Events lasting >45 seconds. ATP production through ATP-PC, glycolysis, and aerobic systems. 70% anaerobic/30% aerobic at 60 seconds. 50% anaerobic/50% aerobic at 2 minutes. © McGraw Hill 16  Metabolic responses to exercise: influence of duration and intensity 2 Metabolic Responses to prolonged exercise (more than 10 minutes) in cool environment. ATP production primarily from aerobic metabolism. Steady-state oxygen uptake can generally be maintained during submaximal exercise (below lactate threshold). Prolonged exercise in a hot and humid environment or at high intensity. Results in upward drift in oxygen uptake over time due to increases in body temperature and increasing blood levels of epinephrine and norepinephrine. © McGraw Hill 17  Impact of exercise intensity and ambient temperature on VO2 during exercise Exercise at 50% VO2max in a hot/humid environment Exercise at 75% VO2max in a cool environment Access the text alternative for slide images. Figure 4.6 © McGraw Hill 18  Metabolic responses to incremental exercise Oxygen uptake increases linearly until maximal oxygen uptake (VO2 max) is achieved. No further increase in VO2 with increasing work rate. “Physiological ceiling” for delivery of O2 to muscle. Influenced by genetics and training. Physiological factors influencing VO2 max. Maximum ability of cardiorespiratory system to deliver oxygen to the muscle. Ability of muscles to use oxygen and produce ATP aerobically. © McGraw Hill 19  Oxygen consumption (VO2) during an incremental exercise test Access the text alterative for slide images. Figure 4.7 © McGraw Hill 20  How do you verify that VO2 max has been reached during an incremental exercise test? A Closer Look 4.2 Verification of VO2 max-key points. Gold Standard for verification of VO2 max is a plateau in O2 consumption with increase in work rate. Most subjects do not achieve a plateau in O2 consumption during an incremental exercise test. If a plateau in O2 consumption is not achieved, what secondary criteria can confirm VO2 max has been achieved? Suggested criteria include: Reaching age-predicted max heart rate (+/- 10 beats/min). Achieving blood lactate concentration of 8 mM or higher. Attaining a respiratory exchange ratio of 1.15 or higher. Research reveals that these criterial do not always “prove” that VO2 max has been reached. © McGraw Hill 21  Incremental exercise and lactate threshold Lactate threshold is the work rate at which blood lactic acid rises systematically during incremental exercise. Appears at around 50 to 60% VO2 max in untrained subjects. Occurs at higher work rates (65 to 80% VO2 max) in endurance trained subjects. Lactate threshold has also been called: Anaerobic threshold. Onset of blood lactate accumulation (O B L A). Exercise intensity at which blood lactate levels reach 4 m m o l per L. © McGraw Hill 22  Lactate threshold Access the text alterative for slide images. Figure 4.8 © McGraw Hill 23  Possible explanations for the lactate threshold Low muscle oxygen (hypoxia). Recruitment of fast-twitch muscle fibers. LDH isozyme in fast fibers promotes lactic acid formation. Reduced rate of lactate removal from the blood. Accelerated glycolysis. N A D H produced faster than it is shuttled into mitochondria. Excess N A D H in cytoplasm converts pyruvic acid to lactic acid. © McGraw Hill 24  Mitochondrial hydrogen shuttle system and lactate production Access the text alterative for slide images. Figure 4.9 © McGraw Hill 25  Possible mechanisms for lactate threshold Access the text alterative for slide images. Figure 4.10 © McGraw Hill 26  Does lactate production during exercise cause muscle soreness? Winning Edge 4.1 Some athletes believe that lactate promotes muscle soreness following exercise training-Research does not support this claim. Lactate removal from blood is rapid (within 60 minutes) following exercise (Figure 4.4). If lactate production caused muscle soreness, sprinters (track athletes that run 100 to 400 meter events) would experience soreness following every training session. Muscle soreness is rate following routine workout. What causes delayed onset muscle soreness? Likely microscopic injury to muscle fibers (chapter 21). © McGraw Hill 27  Practical uses of lactate threshold Prediction of endurance performance (for example, 10K run). Combined with running economy. Planning training programs. Marker of training intensity. Select a training HR based on lactate threshold. Training near (just below) lactate threshold is effective in shifting lactate threshold to right. © McGraw Hill 28  Removal of blood lactate following exercise Closer Look 4.1 Access the text alterative for slide images. Figure 4.4 © McGraw Hill 29  Estimation of fuel utilization during submaximal exercise 1 Measurement of respiratory exchange ratio provides a noninvasive technique to estimate fuel utilization during exercise. The respiratory exchange ratio (R) is the ratio of carbon dioxide produced to the oxygen consumed (VCO2/VO2). In order for R to be used as an estimate of substrate utilization during exercise, the subject must be in a steady-state. This is important because only during steady-state exercise are the VCO2 and VO2 reflective of metabolic exchange of gases in tissues. The caloric equivalent for oxygen is 4.7 kcal per L when fat alone is used and 5.0 kcal per L when carbohydrate is the only fuel (approximately 6% difference between fuels). Using R to estimate fuel utilization assumes that protein is NOT used as a fuel during exercise. © McGraw Hill 30  Estimation of fuel utilization during submaximal exercise 2 Measurement of pulmonary gas exchange provides a noninvasive technique to estimate fuel utilization during exercise and involves measurement of respiratory exchange ratio (R). VCO2 R= VO2 Measurement must be performed during steady state exercise (that is below lactate threshold). Assumes that “0” protein is used as a fuel during exercise. © McGraw Hill 31  Estimation of fuel utilization during submaximal exercise R for fat (palmitic acid). C16H32O2 + 23 O2 → 16 CO2 + 16 H2O VCO2 16 CO2 R= = = 0.70 VO2 23 O2 R for carbohydrate (glucose) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O VCO2 6 CO2 R= = = 1.00 VO2 6 O2 © McGraw Hill 32  Percentage of fat and carbohydrate metabolized determined by R R % Fat % Carbohydrate kcal · L−1 O2 0.70 100 0 4.69 0.75 83 17 4.74 0.80 67 33 4.80 0.85 50 50 4.86 0.90 33 67 4.92 0.95 17 83 4.99 1.00 0 100 5.05 SOURCE: Knoebel, Leon K. “Energy Metabolism,” Physiology. Boston, MA: Little Brown & Company, 1984. © McGraw Hill 33  Factors governing fuel selection during exercise Fuel selection during exercise is influenced by several factors including: Exercise intensity. Exercise duration. Availability of fuels (for example, availability of muscle glycogen and glucose in blood and availability of free fatty acids). © McGraw Hill 34  Exercise intensity and fuel selection 1 Low-intensity exercise (70% VO2 max). Carbohydrates are primary fuel. © McGraw Hill 35  Exercise intensity and fuel selection 2 “Crossover” concept. Describes the shift from fat to C H O metabolism as exercise intensity increases. Due to: Recruitment of fast muscle fibers. Increasing blood levels of epinephrine stimulate glycogen breakdown. © McGraw Hill 36  Exercise intensity and fuel utilization during exercise: crossover concept Access the text alterative for slide images. Figure 4.11 © McGraw Hill 37  McArdle’s syndrome: a genetic error in muscle glycogen metabolism Clinical Application 4.1 Individuals with McArdle’s Syndrome cannot synthesize the muscle enzyme phosphorylase due to genetic mutation; this results in the inability to break down muscle glycogen. McArdle’s Syndrome patients do not produce lactate during an incremental exercise test and complain of exercise intolerance and muscle pain. © McGraw Hill 38  Exercise duration and fuel selection 1 Prolonged, low-intensity exercise. Shift from carbohydrate metabolism toward fat metabolism. Due to an increased rate of lipolysis. Breakdown of triglycerides glycerol + FFA. By enzymes called lipases. Stimulated by rising blood levels of several hormones (chapter 5). © McGraw Hill 39  Exercise duration and fuel selection 2 Access the text alterative for slide images. Figure 4.12 © McGraw Hill 40  Interaction of fat and C H O metabolism during exercise “Fats burn in the flame of carbohydrates.” Glycogen is depleted during prolonged high-intensity exercise. Reduced rate of glycolysis and production of pyruvate. Reduced Citric acid (Krebs) cycle intermediates. Reduced fat oxidation. Fats are metabolized by Krebs cycle. © McGraw Hill 41  Carbohydrate supplementation during exercise improves endurance performance Winning Edge 4.2 The depletion of muscle and blood carbohydrate stores contributes to fatigue. Ingestion of carbohydrates can improve endurance performance. During submaximal (90 minutes) exercise. 30 to 60 grams of carbohydrate per hour are required. May also improve performance in shorter, higher intensity events (greater than or equal to 45 minutes duration). © McGraw Hill 42  What exercise intensity is best for burning fat? 1 Prolonged exercise at low intensity (approximately 20% VO2 max). High percentage of energy expenditure (approximately 66%) derived from fat. However, total energy expended is low (3 kcal min−1) Total fat oxidation is also low (2 kcal min−1) Prolonged exercise at higher intensities (approximately 60% VO2 max). Lower percentage of energy (approximately 33%) from fat Total energy expended is higher (9 kcal min−1) Total fat oxidation is also higher (3 kcal min−1) © McGraw Hill 43  What exercise intensity is best for burning fat? 2 FATmax. Highest rate of fat oxidation. Reached just before lactate threshold. © McGraw Hill 44  Impact of exercise intensity on fat metabolism Access the text alterative for slide images. Figure 4.13 © McGraw Hill 45  Sources of fuel supply during exercise Carbohydrate. Muscle glycogen. Blood glucose (diet and liver). Free fatty acids. Muscle fat stores. White adipocytes-numerous locations in body. © McGraw Hill 46  Table 4.2: Principal Storage Sites of Carbohydrate and Fat in the Body of a Healthy, Nonobese (20% Body Fat), 70-kg Male Subject 1 Storage Site Mixed Diet Carbohydrate (C H O) Low-C H O Diet High-C H O Diet Liver 60 g (240 kcal or 90 g (360 kcal or 1507 kJ)