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 PHYSIOLOGY Theory and Application to Fitness and Performance (5 th  Ed) Scott K. Powers & Edward T. Howley Presented and Updated by MOHD SANI MADON (PhD)

Transcript of Lecture 5 (Exercise Metabolism)

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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

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The Cori Cycle: Lactate As a

Fuel Source

Fig 4.16