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Chapter 4 Exercise Metabolism.

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Presentation on theme: "Chapter 4 Exercise Metabolism."— Presentation transcript:

1 Chapter 4 Exercise Metabolism

2 Timing, Energy Use, and Control
What are the steps that occur going from rest to exercise back to rest? How do we know what’s happening inside the body - external indicators? How are the energy demands supplied in the time necessary? What are the limitations that prevent us all from being world record holders?

3 Fuel During Exercise Limited or unlimited? Can we add more?
How do we get access?

4 Sources of Fuel During Exercise
Carbohydrate Blood glucose Muscle glycogen Fat Plasma FFA (from adipose tissue lipolysis) Intramuscular triglycerides Protein Only a small contribution to total energy production (only ~2%) May increase to 5-15% late in prolonged exercise Blood lactate Gluconeogenesis via the Cori cycle

5 Estimation of Fuel Utilization During Exercise
First - need to understand oxygen uptake.

6 Oxygen Uptake Ventilation vs. Respiration

7 Oxygen Uptake Ventilation - moving air into and out of the lungs – breathing Stimulated by CO2 in the blood Air exhaled from the lungs is missing some oxygen and has new CO2 added

8 Oxygen Uptake Respiration – movement of gasses – oxygen and carbon dioxide Pulmonary – lungs to blood, blood to lungs Cellular – blood to tissues, tissues to blood Tied to metabolism O2 needed for metabolism CO2 made from metabolism

9 Oxygen Uptake . VO2 – rate volume of oxygen used by the body each minute Absolute units = liters/min Relative units = ml/kg/min VCO2 – rate volume of carbon dioxide produced by the body each minute VE – rate volume of air exhaled each minute Absolute units = liters/minute . .

10 Estimation of Fuel Utilization During Exercise
During steady state exercise VCO2 and VO2 reflective of O2 consumption and CO2 production at the cellular level . .

11 Estimation of Fuel Utilization During Exercise
Respiratory exchange ratio (RER or R) RER = VCO2 VO2 Indicates fuel utilization 0.70 = 100% fat 0.85 = 50% fat, 50% CHO 1.00 = 100% CHO . .

12 Estimation of Fuel Utilization During Exercise
Fat Oxidation (metabolism) C16H32O O CO H2O RER= VCO2 / VO2 = 16 CO2 / 23 O2 = 0.70 . .

13 Estimation of Fuel Utilization During Exercise
Glucose Oxidation (metabolism) C6H12O6 + 6 O CO2 + 6 H2O RER = VCO2 / VO2 = 6 CO2 / 6 O2 = 1.0 . .

14 Exercise Intensity and Fuel Selection
. Low-intensity exercise (<30% VO2max) Fats are primary fuel High-intensity exercise (>70% VO2max) CHO are primary fuel .

15 Effect of Exercise Intensity on Muscle Fuel Source

16 Exercise Intensity and Fuel Selection
“Crossover” concept Describes the shift from fat to CHO metabolism as exercise intensity increases Due to: Recruitment of muscle fibers that need fuel quickly Increasing blood levels of epinephrine that stimulates glycogenolysis

17 Illustration of the “Crossover” Concept

18 Exercise Duration and Fuel Selection
During prolonged exercise there is a shift from CHO metabolism toward fat metabolism Increased rate of lipolysis Breakdown of triglycerides into glycerol and free fatty acids (FFA) Stimulated by rising blood levels of epinephrine

19 Shift From CHO to Fat Metabolism During Prolonged Exercise

20 Interaction of Fat and CHO Metabolism During Exercise
It is not all one or all the other Carbohydrate is a key material Carbohydrate is the brain’s fuel source Run low = physical fatigue Run low = mental stress (BONK)

21 Interaction of Fat and CHO Metabolism During Exercise
Some carbohydrate must be present in order for fat to be metabolized. Physiologic strategy: do what is necessary to “spare” carbohydrate.

22 Interaction of Fat and CHO Metabolism During Exercise
“Fat burns in the flame of carbohydrates” When glycogen is depleted during prolonged high-intensity exercise Reduced rate of glycolysis and production of pyruvate Reduced Krebs cycle intermediates Reduced fat oxidation Fats are metabolized by Krebs cycle

23 Effect of Exercise Duration on Muscle Fuel Source

24 Rest-to-Exercise Transitions
Light switch & energy example

25 Rest-to-Exercise Transitions
Oxygen uptake increases Reaches steady state within 1-4 minutes Oxygen deficit Lag in oxygen uptake at the beginning of exercise Suggests anaerobic pathways contribute to total ATP production After reaching steady state, ATP requirement is met primarily aerobically

26 The Oxygen Deficit

27 Recovery From Exercise: Metabolic Responses
EPOC (formerly known as oxygen debt) Excess post-exercise oxygen consumption Elevated VO2 for several minutes immediately following exercise Aerobic metabolism provides the energy to recycle ADP to ATP .

28 Recovery From Exercise: Metabolic Responses
“Fast” portion of EPOC Resynthesis of stored PC Replacing muscle and blood O2 stores

29 Recovery From Exercise: Metabolic Responses
“Slow” portion of EPOC Elevated body temperature and catecholamines Conversion of lactic acid to glucose (Cori Cycle - gluconeogenesis)

30 Oxygen Deficit and Debt During Light-Moderate and Heavy Exercise

31 Metabolic Response to Exercise: Incremental Exercise
= Incremental increase in intensity

32 Metabolic Response to Exercise: Incremental Exercise
Oxygen uptake increases linearly until VO2max is reached No further increase in VO2 with increasing work rate . .

33 Changes in Oxygen Uptake With Incremental Exercise

34 Fate of Lactate Where does it go? -During anaerobic metabolism
-During aerobic metabolism -After exercise

35 Fate of Lactate Anerobic metabolism
Lactate can stay in the cell and build up Hydogens inhibit PFK – slow glycolysis Fatigue and discomfort Decreased performance Lactate can leave the cell and go into the blood Measurable in millimoles per liter (mM/liter) Lactate can be used by “aerobic” cells – reconvert to pyruvate, etc.

36 Lactate Threshold The point at which blood lactic acid suddenly rises during incremental exercise Also called the anaerobic threshold Also called OBLA – onset of blood lactic acid

37 Mechanisms to Explain the Lactate Threshold

38 Lactate Threshold Practical use as a marker of exercise intensity
High intensity needs anaerobic metab =OBLA The intensity cannot last for long inhibit PFK with lactic acid – high intensity run out of glycogen/glucose – high inten. + duration

39 Lactate Threshold Practical uses in prediction of performance
High threshold compared to max capacity = ability to remain at “low intensity” when others might be at “high intensity” Ex. Top marathoners remain “aerobic” while running faster than 5 min/mile

40 Identification of the Lactate Threshold

41 Other Mechanisms for the Lactate Threshold
Failure of the mitochondrial hydrogen shuttle to keep pace with glycolysis Excess NADH in sarcoplasm favors conversion of pyruvic acid to lactic acid Type of LDH Enzyme that converts pyruvic acid to lactic acid LDH in fast-twitch muscle fibers favors formation of lactic acid

42 Effect of Hydrogen Shuttle and LDH on Lactate Threshold

43 Questions: Can lactate be removed faster?
What does training do to OBLA / lactate threshold? Where does the lactate ultimately go?

44 Removal of Lactic Acid Following Exercise

45 Training Effect on OBLA
Endurance Training “Grow” more mitochondria Use aerobic metab. to supply ATP at higher intensities (less lactate produced) More places for lactate to go Greater and thus faster LA removal / use

46 The Cori Cycle: Lactate As a Fuel Source

47 Lactate as Fuel for the Heart
Heart is the ultimate “aerobic” muscle Converts lactate to pyruvate easily LDH in slow-twitch muscle fibers favors formation of pyruvate Makes ATP through aerobic metabolism with pyruvate as the substrate

48 Fat as fuel Why is fat an economical fuel source?

49 Comparing CHO and FAT 1g of CHO = 4kcal 1g of fat = 9kcal
1g of CHO needs g H2O for storage 1g of fat = 9kcal 1g of fat needs no H2O for storage So the energy equivalent of CHO in 1g of fat requires 2g CHO and 6g H2O This is 8g of weight

50 So…….. To gain the energy equivalent of 1 lb of fat it would take 2 lb CHO + 6 lb H2O = 8 total lb of weight

51 So…….. A 5 lb fat gain would equal a 40 lb CHO gain 1. WOW !!!! 2. Energy efficient?

52 Note: Too much of a good thing is never good, however.

53 Questions?

54 End

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