Exercise Metabolism Dr. Kyle Coffey

1. Exercise MetabolismDr. Kyle Coffey Week 3&4

2. Exercise • Challenge to bioenergetics of the body • 15-25 times the total energy expenditure Where do you think the highest increase in energy utilization over rest occurs?!

3. At Rest • 100% of E utilized/required to sustain bodily functions is from aerobic metabolism • Blood lactate low and steady • O2 consumption • 3.5 ml of O2 per kg of body weight per minute (1 MET)

4. Rest to Exercise Transition • Rest to light/moderate exercise • O2 consumption/ATP production increases rapidly • Steady state within 1-4 minutes • Initially anaerobic • Switches fully to aerobic at steady state

5. Anaerobic ATP Sources

6. Oxygen Deficit • Lag in oxygen uptake at beginning of exercise • “difference between oxygen uptake in the first few minutes of exercise and an equal time period after steady state has been obtained” • What’s the cause? Can we minimize oxygen deficit? If so, how? • TRAINING (more on this later) What adaptations occur with trained versus untrained clients/athletes? • Muscular and cardiovascular

8. Metabolic Responses to Exercise • First 1–5 seconds of exercise • ATP through ATP-PC system • Intense exercise longer than 5 seconds • Shift to ATP production via glycolysis • Events lasting longer than 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

9. Metabolic Responses to Prolonged Exercise • Prolonged exercise (>10 minutes) • ATP production primarily from aerobic metabolism • Steady-state oxygen uptake can generally be maintained during submaximal exercise • Prolonged exercise in a hot/humid environment or at high intensity • Upward drift in oxygen uptake over time due to body temperature and rising epinephrine and norepinephrine WHAT DOES THIS MEAN?!

10. High work rate (>75% VO2 max) Hot and humid environment (at same work rate)

11. Metabolic Responses to Incremental Exercise • Oxygen uptake increases linearly with HR until maximal oxygen uptake (VO2 max) is reached

12. Recovery from Exercise: Metabolic • Metabolic rate does not fall instantaneously • Resting levels by 5 minutes after exercise (steady state) • Resting levels by 14 minutes after exercise (non-steady state) • PCr stores replenished during recovery/resting • Glycolysis used during exercise if anaerobic systems needed

13. Oxygen Debt • Excess Post-Exercise Oxygen Consumption (EPOC) • Excess oxygen uptake, above that consumed during rest, following exercise • Increases with the amount of time that was exercised • Can we reduce this? • TRAINING (more on this later)

14. R S S S S R

15. Moderate exercise Heavy, exhausting exercise

16. Lactate Formation During Exercise

17. Lactate Threshold • The point at which blood lactic acid rises systematically during incremental exercise • Appears at ~50–60% VO2 max in untrained subjects • At higher work rates (65–80% VO2 max) in trained subjects • Also called: • Anaerobic threshold (no longer) • Onset of blood lactate accumulation (OBLA) • Blood lactate levels reach 4+ mmol/L What can training do to improve lactate threshold? • Improving ability to reduce lactate levels or use as fuel

18. Lactate Threshold

19. Video • How is an athlete’s lactate threshold determined? • REMINDER: typically VO2max and lactate threshold are used in conjunction to determine training zones

20. Fate of Lactate • Resynthesize depleted liver glycogen • Conversion to glucose in the liver via gluconeogensis (Cori cycle) • Oxidized to pyruvate  Krebs Cycle and Electron Transport Chain = ATP!

21. Cori Cycle

22. Lactate Removal

23. Use of Lactate Threshold • Prediction of overall performance • Combined with VO2 max • Previously used as indicator of anaerobic threshold • Not anymore! • Planning training programs • Marker of training intensity • Choose a training HR based on LT

24. Estimation of % Fuel Utilization DURING Exercise • Respiratory Exchange Ratio (RER) • RER refers to the ratio of carbon dioxide output to the volume of oxygen consumed (VCO2/VO2) • Referred to as the respiratory quotient during steady state conditions • Typically refer to non-protein RER • WHY?

25. VCO2 R = VO2 VCO2 16 CO2 R = = = 0.70 VO2 23 O2 VCO2 6 CO2 R = = = 1.00 VO2 6 O2 Respiratory Exchange Ratio (RER) • Respiratory exchange ratio (RER or R) • R for fat (palmitic acid) • R for carbohydrate (glucose) C16H32O2 + 23 O2 16 CO2 + 16 H2O C6H12O6 + 6 O2 6 CO2 + 6 H2O

27. Exercise Intensity and Fuel Selection • Low-intensity exercise (<30% VO2 max) • Fats are primary fuel • High-intensity exercise (>70% VO2 max) • Carbohydrates are primary fuel Example • At low exercise intensities (~20% VO2 max) • High percentage of energy expenditure (~60%) derived from fat • At higher exercise intensities (~50% VO2 max) • Lower percentage of energy (~40%) from fat

28. REMINDER • There is an abundance of fat energy in reserve (storage), but only a small quantity of CHO (glycogen)

29. Why Fats at Low Intensities? • Larger stores, almost unlimited • Greater energy yield (ATP) per molecule • O2 requirement is not limiting

30. Why Carbs at High Intensities? • Capable of anaerobic energy production (fast) • O2Efficiency • Requires less O2 than Fat for oxidative phosphorylation • Closer proximity to mitochondria This explains why high intensity, endurance activities are limited by CHO stores and not fat stores! How can we affect this? 2 ways!

31. Fat Metabolism at Different Intensities

32. Exercise Intensity & Fuel Selection

33. Crossover Concept • Describes the shift from fat to CHO metabolism as exercise intensity increases • Most notably in high intensity, endurance activities close to lactate threshold • WHY? • Can training impact?

34. Crossover Concept (Untrained)

35. Crossover Concept (Trained)

36. Carbohydrate Loading • 1960s – carbohydrate loading revolution! • Glycogen supercompensationweek preceding a competition • Approach: train intensely while maintaining a low-carbohydrate diet early in the week to deplete glycogen stores progressing to decreasing intensity and a high-carbohydrate diet • More recent research • 65-70% greater than normal carbohydrate the week prior to competition is sufficient

37. Exercise Intensity and Fuel Section (Cont’d) • Prolonged (>30 min), low-mod intensity exercise • Shift from carbohydrate metabolism toward fat metabolism • O2 is not limiting factor

38. Carbs to Fat with Prolonged Exercise (constant low intensity)

39. Must we burn fat to lose fat? Examples: %VO2max Run Speed Distance Time Relative Fat Absolute Fat Total kcal 25% 10 min/mile 3 mile 30 min 50% 19g 350 65% 7 min/mile 3 mile 21 min 35% 14g 350 85% 5 min/mile 3 mile 15 min 20% 8g 350

40. Must we burn fat to lose fat? Examples: %VO2max Run Speed Distance Time Relative Fat Absolute Fat Total kcal 25% 10 min/mile 3 mile 30 min 50% 19g 350 65% 7 min/mile 4 mile 30 min 35% 19g 500 85% 5 min/mile 6 mile 30 min 20% 15g 700