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Exercise Metabolism

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When glycogen is depleted during prolonged high-intensity exercise ... High threshold compared to max capacity = ability to remain at 'low intensity' ... – PowerPoint PPT presentation

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Title: Exercise Metabolism


1
Exercise Metabolism
Chapter 4
2
Timing, Energy Use, and Control
  • What are the steps that occur going from rest to
    exercise back to rest?
  • How do we know whats 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
  • Absolute units liters/min
  • Relative units ml/kg/min
  • 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)
  • C16H32O2 23 O2 16 CO2 16 H2O
  • RER VCO2 / VO2 16 CO2 / 23 O2
  • 0.70

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

.
.
14
Exercise Intensity and Fuel Selection
.
  • Low-intensity exercise (lt30 VO2max)
  • Fats are primary fuel
  • High-intensity exercise (gt70 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 brains 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 CHO needs 3 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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