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Lecture 5 (Exercise Metabolism)
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Transcript of Lecture 5 (Exercise Metabolism)
8/12/2019 Lecture 5 (Exercise Metabolism)
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(c) 2004 The McGraw-Hill Companies, Inc. All rights reserved.
3/24/2014 UPSI 2006 1
Chapter 4: Exercise Metabolism
EXERCISE PHYSIOLOGYTheory and Application to Fitness and Performance
(5th Ed)
Scott K. Powers & Edward T. Howley
Presented and Updated by
MOHD SANI MADON (PhD)
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Objectives
Discuss the relationship between exercise
intensity/duration and the bioenergetic pathways
Define the term oxygen deficit
Define the term lactate threshold
Discuss several possible mechanisms for the
sudden rise in blood-lactate during incremental
exercise List the factors that regulate fuel selection during
different types of exercise
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Objectives
Explain why fat metabolism is dependent on
carbohydrate metabolism
Define the term oxygen debt Give the physiological explanation for the
observation that the O2 dept is greater
following intense exercise when compares to
the O2 debt following light exercise
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Rest-to-Exercise Transitions
Oxygen uptake increases rapidly
Reaches steady state within 1-4 minutes
Oxygen deficit
Lag in oxygen uptake at the beginning ofexercise
Suggests anaerobic pathways contribute tototal ATP production
After steady state is reached, ATPrequirement is met through aerobic ATPproduction
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The Oxygen Deficit
Fig 4.1
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Differences in VO2 Between
Trained & Untrained Subjects
Fig 4.2
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Recovery From Exercise
Metabolic Responses Oxygen debt or
Excess post-exercise oxygen consumption (EPOC)
Elevated VO2 for several minutes immediately followingexercise
“Fast” portion of O2 debt Resynthesis of stored PC
Replacing muscle and blood O2 stores
“Slow” portion of O2 debt
Elevated Heart rate and breathing, energy need
Elevated body temperature, metabolic rate
Elevated Epinephrine & Norepinephrine, metabolic rate
Conversion of lactic acid to glucose (gluconeogenesis)
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Oxygen Deficit and Debt During
Light-Moderate and Heavy Exercise
Fig 4.3
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Removal of Lactic Acid
Following Exercise
Fig 4.4
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Fig 4.5
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Metabolic Response to Exercise
Short-Term Intense Exercise
High-intensity, short-term exercise (2-20
seconds) ATP production through ATP-PC system
Intense exercise longer than 20 seconds
ATP production via anaerobic glycolysis
High-intensity exercise longer than 45 seconds
ATP production through ATP-PC, glycolysis, and
aerobic systems
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Metabolic Response to Exercise
Prolonged Exercise Exercise longer than 10 minutes
ATP production primarily from aerobic
metabolism Steady state oxygen uptake can generally be
maintained
Prolonged exercise in a hot/humid
environment or at high intensity Steady state not achieved
Upward drift in oxygen uptake over time
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Upward Drift in Oxygen Uptake
During Prolonged Exercise
Fig 4.6
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Metabolic Response to Exercise
Incremental ExerciseVO2 – Ability to Deliver & Use Oxygen
Oxygen uptake increases linearly until VO2max is reached No further increase in VO2 with increasing work
rate
Physiological factors influencing VO2max
Ability of cardiorespiratory system to deliver oxygen to muscles
Ability of muscles to use oxygen and produce ATP aerobically
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Changes in Oxygen Uptake
With Incremental Exercise
Fig 4.7
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Lactate Threshold
The point at which blood lactic acidsuddenly rises during incremental exercise
Also called the anaerobic threshold
Mechanisms for lactate threshold
Low muscle oxygen
Accelerated glycolysis
Recruitment of fast-twitch muscle fibers
Reduced rate of lactate removal from the blood
Practical uses in prediction of performance
and as a marker of exercise intensity
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Identification of the
Lactate Threshold
Fig 4.8
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Mechanisms to Explain the
Lactate Threshold
Fig 4.10
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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 fibers favors formation of
lactic acid
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Effect of Hydrogen Shuttle and
LDH on Lactate Threshold
Fig 4.9
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Estimation of Fuel Utilization
During Exercise
Respiratory exchange ratio (RER or R) VCO2 / VO2
Fat (palmitic acid) = C16H32O2
C16H32O2 + 23O2 16CO2 + 16H2O + ?ATP
R = VCO2/VO2 = 16 CO2 / 23O2 = 0.70
Glucose = C6H12O6 C6H12O6 + 6O2 6CO2 + 6H2O + ?ATP
R = VCO2/VO2 = 6 CO2 / 6O2 = 1.00
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Estimation of Fuel Utilization
During Exercise
Indicates fuel utilization 0.70 = 100% fat
0.85 = 50% fat, 50% CHO
1.00 = 100% CHO
During steady state exercise
VCO2 and VO2 reflective of O2 consumption
and CO2 production at the cellular level
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Exercise Intensity and Fuel
Selection
Low-intensity exercise (<30% VO2max)
Fats are primary fuel
High-intensity exercise (>70% VO2max)
CHO are primary fuel
“Crossover” concept
Describes the shift from fat to CHO
metabolism as exercise intensity increases Due to:
Recruitment of fast muscle fibers
Increasing blood levels of epinephrine
Ill t ti f th
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Illustration of the
“Crossover” Concept
Fig 4.11
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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
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Shift From CHO to Fat Metabolism
During Prolonged Exercise
Fig 4.13
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Interaction of Fat and CHO
Metabolism During Exercise
“Fats burn in a carbohydrate flame”
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
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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
Eff t f E i I t it
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Effect of Exercise Intensity on
Muscle Fuel Source
Fig 4.14
Eff t f E i D ti
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Effect of Exercise Duration on
Muscle Fuel Source
Fig 4.15