MEDI/EXSC221 Bioenergetics & Measuring Energy Use 2023 PDF

Bioenergetics & Measuring Energy Use MEDI/EXSC221 Lecture Objectives Describe how Energy and Oxygen consumption are measured in a practical setting Indirect calorimetry Describe energy systems used for different activities, intensities and duration Briefly discuss energy transfe...

Bioenergetics & Measuring Energy Use MEDI/EXSC221 Lecture Objectives Describe how Energy and Oxygen consumption are measured in a practical setting Indirect calorimetry Describe energy systems used for different activities, intensities and duration Briefly discuss energy transfer and energy stores used in exercise Reading Chapter 6 & 8. Energy Transfer in the Body & Measuring Energy Use McArdle, W.D., Katch, F.I. and Katch, V.L. Exercise Physiology: Nutrition, Energy and Human Performance. Lippingcott, Williams and Wilkins, Sydney, NSW, 2014. ISBN/ISSN: 9781451191554. Energy Use in Humans  Total Daily Energy Expenditure (TDEE) Three major components: 1. Physical Activity (15-30%) 2. Dietary Induced Thermogenesis (~10%) 3. Resting Metabolic Rate (~60-75%) Lean muscle mass Your Turn (Week 4 Forum): What are the average energy expenditure (kj/day) for a male and female? Why is this Answers will be discussed in important? tutorial and on forum We Use Energy to Breathe, think, move… Measuring Energy Use in Humans Type in Olympic Cyclist V’s Toaster: Can He Power It? OR https://www.youtube.com/watch?v=S4O5voOCqAQ Measuring Energy Use in Humans  Methods Used to Measure Energy Use In Humans Doubly Labeled Water: Isotope based method In free living – in the field Process: Measure baseline levels in urine & saliva consume water with labeled H2 and O2 collect all their excreted urine & saliva measure again calculate difference between elimination rates. How much is used and how much is excreted. Very Expensive Have to collect urine & saliva More detail in text book if you are interested. Chapter 8. Methods Used to Measure Energy Use In Humans Direct Calorimetry (heat production) Any change in water temperature (known volume) reflected the subjects energy use. Indirect Calorimetry (respiratory gas exchange) Open circuit and closed-circuit spirometry  Respiratory Gas Exchange Measuring VO2 and VCO2 Douglas Bag Technique Collect all expired air Measure the fraction of expired O2 and CO2 Measure the volume of expired air (L), then calculate VE from the known time ie. VE L/min Then calculate VO2 VO2 (l.min-1)STPD = VO2inspired – VO2expired Full calculation in your textbook p. 182 Contemporary Techniques The Metabolic Cart Follows same general principles as the Douglas Bag Technique (same equations just done for you!) Differences: 1. Pneumotachometer 2. Mixing Chamber 3. Continuous Sampling 4. Automation  Why is there Measuring VO2 During Exercise an oxygen debt? Anaerobic Contribution 2250 2000 Steady State VO2 (ml/min) 1750 1500 1250 Aerobic Contribution 1000 750 500 Baseline 250 0 -120 -60 0 60 120 180 240 300 360 Time (s)  Lab 2 Measuring the change in cardiorespiratory variables of VO2, HR, VE and VCO2 (and relationship). Energy Use During Different Activities Your Turn (post on weekly forum): 1. Approx. which sport has the highest energy cost? 2. Why? Rowing vs Running vs cycling 2km? Swimming 2miles/hour vs Running 5miles/hour? 3. What factors may come into play? Answers will be discussed in tutorial and on forum Example Exam Question: Which of these two exercises has the greatest energy cost and why?  Influence of Body Mass Relationship Between Body Mass and Oxygen Consumption During Walking (p.202 Chapter 90 Increases in body mass raises energy expended in many activities, especially in weight-bearing exercise With weight-supported exercise (e.g. stationary cycling), the influence of body mass on energy cost decreases considerably For overweight persons, weight-bearing exercise generates a considerable caloric expenditure Expressing energy cost per kg of body mass Compare between individuals Taking into account body mass is really important! Biological Work in Humans Three forms of biological work (energy consuming processes) 1. Chemical: Biosynthesis of cellular molecules 2. Mechanical: Muscle contraction 3. Transport: Transfer of substances among cells  1st Law of Thermodynamics Energy can be transformed from one form to another but can be neither created nor destroyed. Muscle contraction e.g., carbohydrate e.g., ATP e.g., energy used to store e.g., human cycling has carbohydrate as an efficiency of ~20% so glycogen in muscle 80% of energy is lost as heat ATP represents the cell’s “energy currency” ATP forms from adenosine linked to three phosphates Adenosine diphosphate (ADP) forms when ATP joins with water, catalysed by the enzyme adenosine triphosphatase (ATPase) ATP: A Limited Currency Cells contain only a small quantity of ATP so it must continually be resynthesised ATP levels decrease in skeletal muscle only under extreme exercise conditions The body stores 80 to 100 g of ATP at any time under normal resting conditions, enough stored energy to power 2 to 3 seconds of maximal exercise Energy Systems: Metabolic Pathways to Regenerate ATP 1. Phosphagen System (ATP-CP) 2. Anaerobic Glycolysis (glucose/CHO) 3. Aerobic System (CHO) 4. Lipid (fat) Muscles need energy to produce contractions Carbohydrate Glucose (blood) Glycogen (stored form)  Free Fatty Acids Triglyceride (stored form) Protein Amino acids (blood) Body’s Energy Stores ATP ~80-100g –> a few seconds of maximal ex PCr ~600g -> a few more seconds…. Carbohydrate (relatively small stores) Muscles contain ~300 g glycogen Liver contains ~100 g glycogen Blood contains ~10 g glucose (NB: CNS needs glucose!) ~ 8.4 mJ energy In contrast to Lipids: Total store is ~10,000 g (67 kg person @15% body fat) AND, there’s more than twice the energy per gram of lipid than CHO. So, Energy store is ~420 mJ Respiratory Exchange Ratio (RER) It is an estimate of the RQ (respiratory quotient) Ratio of carbon dioxide produced to oxygen used in metabolism Estimates what fuel is predominantly being used during exercise seldom reflects oxidation of one macronutrient, but instead a mixture ̇ 2 / VO RER = VCO ̇ 2 Fat = RER of ~ 0.7 (more oxidated and producing less CO2) Carbohydrate = RER of ~ 1.0 (ratio approximately 1:1) Assumes negligible protein is being used in metabolism Your Turn (discuss on weekly forum): If you were asked what fuel was predominately being use at an RER of 0.85 what would your answer be? Answers will be discussed in tutorial and on forum Example Exam Questions: 1. What would be the predominate fuel source used at an RER of 0.90? 2. What would be some factors effecting RER during exercise? Fat Dynamics During Exercise Light- to moderate- intensity exercise  Fatty acids provide predominant energy source in light- intensity exercise  Energy derives from equal amounts of carbohydrate and lipid in moderate- intensity exercise Take Home Messages Human daily energy expenditure is comprised of 3 components, with exercise/physical activity the most variable Energy use during exercise is commonly measured using indirect calorimetry; gas exchange (Oxygen consumed, and carbon dioxide produced) Activities involving large and many muscle groups generally have the highest energy cost (also consider body weight/against gravity) Carbohydrate and fat are the two primary energy sources and their proportions during exercise can be estimated from the RER (obtained from indirect calorimetry)