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Scott K. Powers • Edward T. Howley
Theory and Application to Fitness and Performance
SEVENTH EDITION
Chapter
Bioenergetics
Presentation prepared by:
Brian B. Parr, Ph.D.
University of South Carolina Aiken
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Chapter 3
Objectives
1. Discuss the functions of the cell membrane, nucleus,
and mitochondria.
2. Define the following terms: (1) endergonic reactions, (2)
exergonic reactions, (3) coupled reactions, and (4)
bioenergetics.
3. Describe the role of enzymes as catalysts in cellular
chemical reactions.
4. List and discuss the nutrients that are used as fuels
during exercise.
5. Identify the high-energy phosphates.
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Chapter 3
Objectives
6. Discuss the biochemical pathways involved in
anaerobic ATP production.
7. Discuss the aerobic production of ATP.
8. Describe the general scheme used to regulate
metabolic pathways involved in bioenergetics.
9. Discuss the interaction between aerobic and
anaerobic ATP production during exercise.
10. Identify the enzymes that are considered rate
limiting in glycolysis and the Krebs cycle.
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Chapter 3
Introduction
• Metabolism
– Sum of all chemical reactions that occur in the body
– Anabolic reactions
• Synthesis of molecules
– Catabolic reactions
• Breakdown of molecules
• Bioenergetics
– Converting foodstuffs (fats, proteins, carbohydrates)
into energy
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Chapter 3
Cell Structure
Cell Structure
• Cell membrane
– Semipermeable membrane that separates the cell
from the extracellular environment
• Nucleus
– Contains genes that regulate protein synthesis
• Molecular biology
• Cytoplasm
– Fluid portion of cell
– Contains organelles
• Mitochondria
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Chapter 3
Cell Structure
A Typical Cell and Its Major Organelles
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Figure 3.1
Chapter 3
Cell Structure
In Summary
 Metabolism is defined as the total of all cellular reactions that
occur in the body; this includes both the synthesis of
molecules and the breakdown of molecules.
 Cell structure includes the following three major parts: (1) cell
membrane, (2) nucleus, and (3) cytoplasm (called sarcoplasm in
muscle).
 The cell membrane provides a protective barrier between the
interior of the cell and the extracellular fluid.
 Genes (located within the nucleus) regulate protein synthesis
within the cell.
 The cytoplasm is the fluid portion of the cell and contains
numerous organelles
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Chapter 3
Cell Structure
A Closer Look 3.1
Molecular Biology and Exercise Science
• Study of molecular structures and events underlying
biological processes
– Relationship between genes and cellular
characteristics they control
• Genes code for specific cellular proteins
– Process of protein synthesis
• Exercise training results in modifications in protein
synthesis
– Strength training results in increased synthesis of
muscle contractile protein
• Molecular biology provides “tools” for understanding the
cellular response to exercise
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Chapter 3
Biological Energy Transformation
Steps Leading to Protein Synthesis
1. DNA contains
information to
produce proteins.
2. Transcription
produces mRNA.
3. mRNA leaves
nucleus and binds to
ribosome.
4. Amino acids are
carried to the
ribosome by tRNA.
5. In translation, mRNA
is used to determine
the arrangement of
amino acids in the
polypeptide chain.
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Figure 3.2
Chapter 3
Biological Energy Transformation
Cellular Chemical Reactions
• Endergonic reactions
– Require energy to be added
– Endothermic
• Exergonic reactions
– Release energy
– Exothermic
• Coupled reactions
– Liberation of energy in an exergonic reaction drives
an endergonic reaction
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Chapter 3
Biological Energy Transformation
The Breakdown of Glucose:
An Exergonic Reaction
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Figure 3.3
Chapter 3
Biological Energy Transformation
Coupled Reactions
The energy given off by the exergonic reaction
powers the endergonic reaction
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Figure 3.4
Chapter 3
Biological Energy Transformation
Oxidation-Reduction Reactions
• Oxidation
– Removing an electron
• Reduction
– Addition of an electron
• Oxidation and reduction are always coupled reactions
• Often involves the transfer of hydrogen atoms rather
than free electrons
– Hydrogen atom contains one electron
– A molecule that loses a hydrogen also loses an
electron and therefore is oxidized
• Importance of NAD and FAD
– Creating ATP
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Chapter 3
Biological Energy Transformation
Oxidation-Reduction Reaction
Involving NAD and NADH
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Figure 3.5
Chapter 3
Biological Energy Transformation
Enzymes
• Catalysts that regulate the speed of
reactions
– Lower the energy of activation
• Factors that regulate enzyme activity
– Temperature
– pH
• Interact with specific substrates
– Lock and key model
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Chapter 3
Biological Energy Transformation
Enzymes Catalyze Reactions
Enzymes lower the energy of activation
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Figure 3.6
Chapter 3
Biological Energy Transformation
The Lock-and-Key Model of
Enzyme Action
a)
b)
c)
Substrate (sucrose)
approaches the
active site on the
enzyme.
Substrate fits into
the active site,
forming enzymesubstrate complex.
The enzyme
releases the
products (glucose
and fructose).
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Figure 3.7
Chapter 3
Biological Energy Transformation
Clinical Applications 3.1
Diagnostic Value of Measuring Enzyme Activity in the Blood
• Damaged cells release enzymes into the blood
– Enzyme levels in blood indicate disease or tissue
damage
• Diagnostic application
– Elevated lactate dehydogenase or creatine kinase in
the blood may indicate a myocardial infarction
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Chapter 3
Biological Energy Transformation
Examples of the Diagnostic
Value of Enzymes in Blood
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Chapter 3
Biological Energy Transformation
Classification of Enzymes
• Oxidoreductases
– Catalyze oxidation-reduction reactions
• Transferases
– Transfer elements of one molecule to another
• Hydrolases
– Cleave bonds by adding water
• Lyases
– Groups of elements are removed to form a double bond or
added to a double bond
• Isomerases
– Rearrangement of the structure of molecules
• Ligases
– Catalyze bond formation between substrate molecules
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Chapter 3
Biological Energy Transformation
Example of the Major Classes
of Enzymes
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Chapter 3
Biological Energy Transformation
Factors That Alter Enzyme Activity
• Temperature
– Small rise in body temperature increases
enzyme activity
– Exercise results in increased body
temperature
• pH
– Changes in pH reduces enzyme activity
– Lactic acid produced during exercise
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Chapter 3
Biological Energy Transformation
The Effect of Body Temperature on
Enzyme Activity
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Figure 3.8
Chapter 3
Biological Energy Transformation
The Effect of pH on Enzyme
Activity
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Figure 3.9
Chapter 3
Fuels for Exercise
Carbohydrates
• Glucose
– Blood sugar
• Glycogen
– Storage form of glucose in liver and muscle
• Synthesized by enzyme glycogen synthase
– Glycogenolysis
• Breakdown of glycogen to glucose
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Chapter 3
Fuels for Exercise
Fats
• Fatty acids
– Primary type of fat used by the muscle
– Triglycerides
• Storage form of fat in muscle and adipose tissue
• Breaks down into glycerol and fatty acids
• Phospholipids
– Not used as an energy source
• Steroids
– Derived from cholesterol
– Needed to synthesize sex hormones
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Chapter 3
Fuels for Exercise
Protein
• Composed of amino acids
• Some can be converted to glucose in the liver
– Gluconeogenesis
• Others can be converted to metabolic intermediates
– Contribute as a fuel in muscle
• Overall, protein is not a primary energy source during
exercise
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Chapter 3
Fuels for Exercise
In Summary
 The body uses carbohydrate, fat, and protein
nutrients consumed daily to provide the necessary
energy to maintain cellular activities both at rest and
during exercise. During exercise, the primary
nutrients used for energy are fats and
carbohydrates, with protein contributing a relatively
small amount of the total energy used.
 Glucose is stored in animal cells as a polysaccharide
called glycogen.
 Fatty acids are the primary form of fat used as an
energy source in cells. Fatty acids are stored as
triglycerides in muscle and fat cells.
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Chapter 3
High-Energy Phosphates
High-Energy Phosphates
• Adenosine triphosphate (ATP)
– Consists of adenine, ribose, and three linked
phosphates
• Synthesis
ADP + Pi  ATP
• Breakdown
ATP
ATPase
ADP + Pi + Energy
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Chapter 3
High-Energy Phosphates
Structure of ATP
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Figure 3.10
Chapter 3
High-Energy Phosphates
Model of ATP as the Universal Energy Donor
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Figure 3.11
Chapter 3
Bioenergetics
Bioenergetics
• Formation of ATP
– Phosphocreatine (PC) breakdown
– Degradation of glucose and glycogen
• Glycolysis
– Oxidative formation of ATP
• Anaerobic pathways
– Do not involve O2
– PC breakdown and glycolysis
• Aerobic pathways
– Require O2
– Oxidative phosphorylation
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Chapter 3
Bioenergetics
Anaerobic ATP Production
• ATP-PC system
– Immediate source of ATP
PC + ADP
Creatine kinase
ATP + C
• Glycolysis
– Glucose  2 pyruvic acid or 2 lactic acid
– Energy investment phase
• Requires 2 ATP
– Energy generation phase
• Produces 4 ATP, 2 NADH, and 2 pyruvate or 2
lactate
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Chapter 3
Bioenergetics
The Winning Edge 3.1
Does Creatine Supplementation Improve Exercise
Performance?
• Depletion of PC may limit short-term, high-intensity exercise
• Creatine monohydrate supplementation
– Increased muscle PC stores
– Some studies show improved performance in short-term, highintensity exercise
• Inconsistent results may be due to water retention and
weight gain
– Increased strength and fat-free mass with resistance training
• Creatine supplementation does not appear to pose health risks
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Chapter 3
Bioenergetics
A Closer Look 3.2
Lactic Acid or Lactate?
• Terms lactic acid and lactate used interchangeably
– Lactate is the conjugate base of lactic acid
• Lactic acid is produced in glycolysis
– Rapidly disassociates to lactate and H+
The ionization of lactic acid forms the
conjugate base called lactate
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Figure 3.12
Chapter 3
Bioenergetics
The Two Phases of Glycolysis
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Figure 3.13
Chapter 3
Bioenergetics
Interaction Between Blood Glucose and
Muscle Glycogen in Glycolysis
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Figure 3.14
Chapter 3
Bioenergetics
Glycolysis: Energy Investment Phase
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Figure 3.15
Chapter 3
Bioenergetics
Glycolysis: Energy Generation Phase
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Figure 3.15
Chapter 3
Bioenergetics
Hydrogen and Electron Carrier Molecules
• Transport hydrogens and associated electrons
– To mitochondria for ATP generation (aerobic)
– To convert pyruvic acid to lactic acid (anaerobic)
• Nicotinamide adenine dinucleotide (NAD)
NAD + 2H+  NADH + H+
• Flavin adenine dinucleotide (FAD)
FAD + 2H+  FADH2
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Chapter 3
Bioenergetics
NADH is “Shuttled” into Mitochondria
• NADH produced in glycolysis must be converted back to
NAD
– By converting pyruvic acid to lactic acid
– By “shuttling” H+ into the mitochondria
• A specific transport system shuttles H+ across the
mitochondrial membrane
– Located in the mitochondrial membrane
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Chapter 3
Bioenergetics
Conversion of Pyruvic Acid to Lactic Acid
The addition of two H+ to pyruvic acid forms NAD and lactic acid
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Figure 3.16
Chapter 3
Bioenergetics
In Summary
 The immediate source of energy for muscular
contraction is the high-energy phosphate ATP. ATP is
degraded via the enzyme ATPase as follows:
ATP
ATPase
ADP + Pi + Energy
 Formation of ATP without the use of O2 is termed
anaerobic metabolism. In contrast, the production of
ATP using O2 as the final electron acceptor is
referred to as aerobic metabolism.
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Chapter 3
Bioenergetics
In Summary
 Exercising skeletal muscles produce lactic acid.
However, once produced in the body, lactic acid is
rapidly converted to its conjugate base, lactate.
 Muscle cells can produce ATP by any one or a
combination of three metabolic pathways: (1) ATPPC system, (2) glycolysis, (3) oxidative ATP
production.
 The ATP-PC system and glycolysis are two
anaerobic metabolic pathways that are capable of
producing ATP without O2.
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Chapter 3
Bioenergetics
Aerobic ATP Production
• Krebs cycle (citric acid cycle)
– Pyruvic acid (3 C) is converted to acetyl-CoA (2 C)
• CO2 is given off
– Acetyl-CoA combines with oxaloacetate (4 C) to form
citrate (6 C)
– Citrate is metabolized to oxaloacetate
• Two CO2 molecules given off
– Produces three molecules of NADH and one FADH
– Also forms one molecule of GTP
• Produces one ATP
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Chapter 3
Bioenergetics
The Three Stages
of Oxidative
Phosphorylation
Figure 3.17
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Chapter 3
Bioenergetics
The Krebs Cycle
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Figure 3.18
Chapter 3
Bioenergetics
Fats and Proteins in Aerobic
Metabolism
• Fats
– Triglycerides  glycerol and fatty acids
– Fatty acids  acetyl-CoA
• Beta-oxidation
– Glycerol is not an important muscle fuel
during exercise
• Protein
– Broken down into amino acids
– Converted to glucose, pyruvic acid, acetylCoA, and Krebs cycle intermediates
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Chapter 3
Bioenergetics
Relationship Between the Metabolism of
Proteins, Carbohydrates, and Fats
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Figure 3.19
Chapter 3
Bioenergetics
Aerobic ATP Production
• Electron transport chain
– Oxidative phosphorylation occurs in the
mitochondria
– Electrons removed from NADH and FADH are
passed along a series of carriers (cytochromes) to
produce ATP
• Each NADH produces 2.5 ATP
• Each FADH produces 1.5 ATP
– Called the chemiosmotic hypothesis
– H+ from NADH and FADH are accepted by O2 to
form water
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Chapter 3
Bioenergetics
The Chemiosmotic Hypothesis of ATP Formation
• Electron transport chain results in pumping of H+ ions
across inner mitochondrial membrane
– Results in H+ gradient across membrane
• Energy released to form ATP as H+ ions diffuse back
across the membrane
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Chapter 3
Bioenergetics
The Electron Transport Chain
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Figure 3.20
Chapter 3
Bioenergetics
Beta Oxidation is the Process of Converting
Fatty Acids to Acetyl-CoA
• Breakdown of triglycerides releases fatty acids
• Fatty acids must be converted to acetyl-CoA to be used
as a fuel
– Activated fatty acid (fatty acyl-CoA) into
mitochondrion
– Fatty acid “chopped” into 2 carbon fragments
forming acetyl-CoA
• Acetyl-CoA enters Krebs cycle and is used for energy
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Chapter 3
Bioenergetics
Beta Oxidation
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Figure 3.21
Chapter 3
Bioenergetics
In Summary
 Oxidative phosphorylation or aerobic ATP
production occurs in the mitochondria as a result of
a complex interaction between the Krebs cycle and
the electron transport chain. The primary role of the
Krebs cycle is to complete the oxidation of
substrates and form NADH and FADH to enter the
electron transport chain. The end result of the
electron transport chain is the formation of ATP and
water. Water is formed by oxygen-accepting
electrons; hence, the reason we breathe oxygen is to
use it as the final acceptor of electrons in aerobic
metabolism.
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Chapter 3
A Closer Look 3.5
Aerobic ATP Tally
A New Look at the ATP Balance
Sheet
• Historically, 1 glucose produced 38 ATP
• Recent research indicates that 1 glucose
produces 32 ATP
– Energy provided by NADH and FADH also
used to transport ATP out of mitochondria.
– 3 H+ must pass through H+ channels to
produce 1 ATP
– Another H+ needed to move the ATP across
the mitochondrial membrane
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Chapter 3
Aerobic ATP Tally
Aerobic ATP Tally Per Glucose Molecule
Metabolic Process
High-Energy
Products
ATP from Oxidative ATP Subtotal
Phosphorylation
Glycolysis
2 ATP
2 NADH
—
5
2 (if anaerobic)
7 (if aerobic)
Pyruvic acid to acetyl-CoA 2 NADH
5
12
Krebs cycle
—
15
3
14
29
32
Grand Total
2 GTP
6 NADH
2 FADH
32
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Chapter 3
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Chapter 3
Efficiency of Oxidative Phosphorylation
Efficiency of Oxidative Phosphorylation
• One mole of ATP has energy yield of 7.3 kcal
• 32 moles of ATP are formed from one mole of
glucose
• Potential energy released from one mole of
glucose is 686 kcal/mole
32 moles ATP/mole glucose x 7.3 kcal/mole ATP
x 100 = 34%
686 kcal/mole glucose
• Overall efficiency of aerobic respiration is
34%
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Chapter 3
Efficiency of Oxidative Phosphorylation
In Summary
 The aerobic metabolism of one molecule of glucose
results in the production of 32 ATP molecules,
whereas the aerobic yield for glycogen breakdown is
33 ATP.
 The overall efficiency of aerobic of aerobic
respiration is approximately 34%, with the remaining
66% of energy being released as heat.
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Chapter 3
Control of Bioenergetics
Control of Bioenergetics
• Rate-limiting enzymes
– An enzyme that regulates the rate of a metabolic
pathway
• Modulators of rate-limiting enzymes
– Levels of ATP and ADP+Pi
• High levels of ATP inhibit ATP production
• Low levels of ATP and high levels of ADP+Pi
stimulate ATP production
– Calcium may stimulate aerobic ATP production
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Chapter 3
Control of Bioenergetics
Example of a Rate-Limiting Enzyme
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Figure 3.22
Chapter 3
Control of Bioenergetics
Factors Known to Affect Rate-Limiting Enzymes
Pathway
Rate-Limiting
Enzyme
Stimulators
Inhibitors
ATP-PC system
Creatine kinase
ADP
ATP
Glycolysis
Phosphofructokinase AMP, ADP, Pi, pH ATP, CP, citrate, pH
Krebs cycle
Isocitrate
dehydrogenase
++
ADP, Ca , NAD
Electron transport Cytochrome Oxidase ADP, Pi
chain
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ATP, NADH
ATP
Chapter 3
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Chapter 3
Control of Bioenergetics
In Summary
 Metabolism is regulated by enzymatic activity. An enzyme that
regulates a metabolic pathway is termed a “rate-limiting”
enzyme.
 The rate-limiting enzyme for glycolysis is phosphofructokinase,
while the rate-limiting enzymes for the Krebs cycle and electron
transport chain are isocitrate dehydrogenase and cytochrome
oxidase, respectively.
 In general, cellular levels of ATP and ADP+Pi regulate the rate of
metabolic pathways involved in the production of ATP. High
levels of ATP inhibit further ATP production, while low levels of
ATP and high levels of ADP+Pi stimulate ATP production.
Evidence also exists that calcium may stimulate aerobic energy
metabolism.
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Chapter 3
Interaction Between Aerobic/Anaerobic ATP Production
Interaction Between Aerobic/Anaerobic ATP
Production
• Energy to perform exercise comes from an interaction
between aerobic and anaerobic pathways
• Effect of duration and intensity
– Short-term, high-intensity activities
• Greater contribution of anaerobic energy systems
– Long-term, low to moderate-intensity exercise
• Majority of ATP produced from aerobic sources
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Chapter 3
Interaction Between Aerobic/Anaerobic ATP Production
Contribution of Aerobic/Anaerobic ATP Production During
Sporting Events
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Figure 3.23
Chapter 3
Interaction Between Aerobic/Anaerobic ATP Production
In Summary
 Energy to perform exercise comes from an
interaction of anaerobic and aerobic
pathways.
 In general, the shorter the activity (high
intensity), the greater the contribution of
anaerobic energy production. In contrast,
long-term activities (low to moderate
intensity) utilize ATP produced from aerobic
sources.
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