MEDI221 2023 Integration Lecture Notes PDF

Lecture 11 Integration lecture: Energy Systems, Fuel Use and Hormones Lecture Objectives To recognise the interplay between energy systems and fuel use during different exercise intensities and durations. Understand what fuels are used, and regulation of fuel use during exercise Kno...

Lecture 11 Integration lecture: Energy Systems, Fuel Use and Hormones Lecture Objectives To recognise the interplay between energy systems and fuel use during different exercise intensities and durations. Understand what fuels are used, and regulation of fuel use during exercise Know the factors that influence fuel use (i.e., intensity, training status), and How fuel use is regulated (i.e., hormones, enzymes) Reading On Moodle: Fuel use during exercise: Chapter from Textbook ‘Biochemistry of Exercise and Training’ (Maughan, Gleeson and Greenhaff). Recap… Your Turn: Post on Weekly Forum Which is the main determinant of fuel selection during exercise?  Example Exam Question What is the proportion of aerobic vs anaerobic energy contribution for the following sports (%)? BMX Racing 100% Anaerobic 100% Aerobic Hockey (Not Goalie) Indoor Soccer Figure 3.23 Powers & Howley textbook Contribution of Aerobic/Anaerobic ATP Production During Sporting Events What determines fuel use in exercise? availability 1. Exercise intensity (rate of 2. Exercise duration energy demand) Fuel depletion (AMP, reduced OAA) Blood flow Oxygen availability Oxygen availability Energy demand Fibre type Your Turn: When will we have a lot of Muscle acidity (H+) AMP in our system? (revision) 4. Prior exercise & training 3. Feeding status If its there we will use it! How many stores do you have? (i.e., in the blood stream) Four Main Fuels For Exercise Muscle Glycogen Blood Glucose (from liver or Stored in stomach) muscle Muscle Triglyceride Blood Fatty Acids (from adipose tissue) Effect of Exercise Intensity on Fuel Selection (Expressed as percent of total energy) 100 % of Total Energy 80 Blood Glucose 60 Muscle Glycogen 40 Plasma FFA Muscle TG 20 0 25 50 75 % VO2max Effect of Exercise Intensity on Fuel Selection (Expressed as rate of energy use, ie., kcal/min) 15 Blood Glucose kcal / min 10 Muscle Glycogen Plasma FFA 5 Muscle TG 0 25 50 75 % VO2max  Your Turn: Do you burn more fat during low or high intensity exercise? Glucose Glycogen 100 FFA IMTG % of Total Energy 80 60 40 What else do you need to 20 consider? 0 25 50 75 % VO2max Muscle Fibre Types (Lec 13) 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 RER low-intensity exercise ~0.7-0.85 Respiratory Exchange Ratio (RER) ሶ 2 / VO RER = VCO ሶ 2 Fat use = lower CO2 produced relative to O2 used. (Ratio lower) CHO use = higher CO2 produced relative to O2 Fig 4.3. Powers & Howley Textbook used. Low-intensity exercise 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 Glycogen Depletion Depends on Exercise Intensity at Start Initially, glucose is used Then fatty acids take over and glucose is recycled LIVER GLYCOGEN lactate MUSCLE Adipose glucose lactate FAT glucose CO2 fatty acids fatty acids CO2 Glycogen Depletion depends on exercise intensity (rate of glycolysis) Figure 11.5 textbook Diet and Training Status Nutrients 2018, 10, 298; doi:10.3390/nu10030298 Glycogen sparing Is important for endurance exercise performance: 1. Carbohydrate ingestion during exercise (>45 min) improves exercise performance Delays fatigue & allows longer duration at higher intensity 2. Trained athletes have a greater reliance on fat for fuel even at intensities >60% intensity More IMTG stores More Mitochondria & aerobic enzymes (greater activity and rate)  Figure 6.17 – textbook Glycolysis Aerobic Metabolism (CHO and Fat) “Fat burns in a carbohydrate flame” Fats can only be oxidised in the presence of carbohydrates Some OAA (oxaloacetate) is needed from pyruvate to completely oxidise Acetyl- CoA Regulation of CHO oxidation during exercise How does fat metabolism (FFA availability) regulate glucose metabolism (to save glycogen stores)? Via the enzyme - PDH activity. PDH regulated by [acetyl-CoA] – if too much acetyl coA carbohydrate oxidation will ↓ Cortisol release ↓glucose uptake, ↑ lipolysis, ↑ gluconeogenesis 4. Mitochondrial entry – formation of Acetyl CoA -PDH regulates entry into mitochondria (controls the flux) -Acetyl-CoA irreversible -(entry point for all metabolic fuels for the Krebs cycle) Enzyme: PDH Pyruvate + NAD+ Acetyl CoA + CO2 + NADH Lecture 11 Regulation of CHO and Fat oxidation PDH Regulation of CHO and Fat oxidation FFA oxidation Blood flow Adrenaline & Insulin Cortisol (if prolonged) CHO oxidation Glucose availability GLUT-4 PDH [acetyl-coA] Adrenaline and Insulin Example Exam Question: Kath and Kim are two Aussies who walk together for fitness/health reasons 45 min each day. Kath’s VO2max is 29 mL/kg/min Kim’s VO2max is 36 mL/kg/min The first 30-min of their walk is flat and use it as a warmup. Q 1. List the energy systems that provide ATP, and circle the primary energy system Q 2. What are the fuel sources are used during this first 30-min, and circle the primary fuel source Q 3. Give two mechanisms that regulate fuel use under these conditions (how and why)? Moderate Exercise Intensity ~65% of VO2max Higher rate of energy demand ↑catecholamines, glucagon Lower adipose tissue blood flow More intramuscular triglycerides and glycogen used Figure 6.16 Textbook Your Turn: What would your ~RER be during moderate intensity exercise (~65% VO2max)? (hint 50:50) Discuss on forum, answer in tutorial.  Maximal fat oxidation occurs at 65% of VO2max Am J Clin Nutr. 2000;72(2):558S-563S. doi:10.1093/ajcn/72.2.558S Your Turn: If catecholamines (Ad. NorAd.) go up during high intensity exercise, why does fat oxidation ↓? Discuss on forum, answer in tutorial. Exercise intensity  Summary points Aerobic: pyruvate → Acetyl CoA (which is further metabolised in Krebs cycle) requires PDH activity Acetyl CoA also entry point of FFA To oxidise Acetyl CoA some OAA is necessary which can only be formed from pyruvate (not from Acetyl CoA, i.e. not from FFA) “Fat burns in a CHO flame” Some glucose can be made from some amino acids, glycerol, lactate Hormones (insulin, catecholamines, cortisol) and metabolites/products (acetylcoA, lactate) play a large role in modifying enzyme activity and transport proteins; THUS SUBSTRATE USE HSL, GLUT4 (insulin, catecholamines) Blood flow Fat vs CHO utilisation