C H A P T E R    4
METABOLISM, ENERGY, AND THE BASIC ENERGY SYSTEMS


Contents
Learning Objectives
w Learn how our bodies change the food we
eat into ATP to provide our muscles with
the energy they need to move.
w Examine three systems that generate energy
for muscles.
w Explore how energy production and
availability can limit performance.
(continued)

Contents
Learning Objectives
w Learn how exercise affects metabolism and
how metabolism can be monitored to
determine energy expenditure.
w Discover the underlying causes and sites of
fatigue in muscles.

Contents
Calorie and Kilocalorie
w Energy in biological systems is measured in calories (cal).
w1 cal is the amount of heat energy needed to raise 1 g of water 1°C from 14.5°C to 15.5°C.
w In humans, energy is expressed in kilocalories (kcal), where 1 kcal equals 1,000 cal.
w People often mistakenly say “calories” when they mean more accurately kilocalories. When we speak
of someone expending 3,000 cal per day, we really mean that person is expending 3,000 kcal per day.

Contents
Energy for Cellular Activity
w Food sources are processed via catabolism—the process of “breaking down.”
w Energy is transferred from food sources to our cells to be stored as ATP.
w ATP is a high-energy compound stored in our cells and is the source of all energy used at rest
and during exercise.
Fuelpump

Energy for muscles
Fuelpump
j0429603 j0295250

Contents
Energy Sources
w At rest, the body uses carbohydrates and fats for energy.
w Protein provides little energy for cellular activity, but serves as building blocks for the
body's tissues.
w During moderate to severe muscular effort, the body relies mostly on carbohydrate for fuel.
Rower

Contents
Carbohydrate
w Readily available (if included in diet) and easily metabolized by muscles
w Once ingested, it is transported as glucose and taken up by muscles and liver and converted to
glycogen
w Glycogen stored in the liver is converted back to glucose as needed and transported by the blood
to the muscles where it is used to form ATP
Plateo'spaghetti
w Glycogen stores are limited, which can affect performance

Contents
Fat
w Provides substantial energy at rest and during prolonged, low-intensity activity
w Body stores of fat are larger than carbohydrate reserves
w Less accessible for metabolism because it must be reduced to glycerol and free fatty acids (FFA)
w Only FFAs are used to form ATP
Candybar
w Fat is limited as an energy source by its rate of energy release




Výsledek obrázku pro resynthesis of ATP



Tables
Body Stores of Fuels and Energy
 g            kcal
Carbohydrates
Liver glycogen 110        451
Muscle glycogen 500 2,050
Glucose in body fluids 15 62
Total 625 2,563
Fat
Subcutaneous and visceral 7,800 73,320
Intramuscular 161 1,513
Total 7,961 74,833
Note. These estimates are based on an average body weight of 65 kg with 12% body fat.

Contents
Protein
w Can be used as an energy source if converted to
glucose via gluconeogenesis
w Can generate FFAs in times of starvation through lipogenesis
w Only basic units of protein—amino acids—can be
used for energy: ~4.1 kcal of energy per g of protein
Burger

Contents
1. ATP-PCr system (phosphagen system)—cytoplasm
2. Glycolytic system—cytoplasm
3. Oxidative system—mitochondria or powerhouses of cell
Basic Energy Systems
Atom

Illustration
ATP MOLECULE


Contents
ATP-PCr System
w This system can prevent energy depletion by quickly reforming ATP from ADP and Pi.
w This process is anaerobic—it occurs without oxygen.
w 1 mole of ATP is produced per 1 mole of
phosphocreatine (PCr). The energy from the breakdown of PCr is not used for cellular work but
solely for regenerating ATP.
Sprinter

Illustration
RECREATING ATP WITH PCr


Contents
Glycogen Breakdown and Synthesis
Glycolysis—Breakdown of glucose; may be anaerobic or aerobic
Glycogenesis—Process by which glycogen is synthesized from glucose to be stored in the liver
Glycogenolysis—Process by which glycogen is broken
into glucose-1-phosphate to be used by muscles
Kayak

Contents
Glycolytic System
w Requires 12 enzymatic reactions to breakdown glucose and glycogen into ATP
w Glycolysis that occurs in glycolytic system is generally anaerobic (without oxygen)
w The pyruvic acid produced by anaerobic glycolysis becomes lactic acid
w 1 mole of glycogen produces 3 mole ATP; 1 mole of glucose produces 2 mole of ATP. The difference
is due to the fact that it takes 1 mole of ATP to convert glucose to glucose-6-phosphate, where
glycogen is converted to glucose-1-phosphate and then to glucose-6-phosphate without the loss of 1
ATP.

Contents
The combined actions of the ATP-PCr and glycolytic systems allow muscles to generate force in the
absence of oxygen; thus these two energy systems are the major energy contributors during the early
minutes of high-intensity exercise.
Did You Know…?
Tennis

Contents
Oxidative System
w Relies on oxygen to breakdown fuels for energy
w Produces ATP in mitochondria of cells
w Can yield much more energy (ATP) than anaerobic systems
Runningman
w Is the primary method of energy production during endurance events

Contents
1. Aerobic glycolysis—cytoplasm
2. Krebs cycle—mitochondria
3. Electron transport chain—mitochondria
Oxidative Production of ATP
Circleofarrows

Illustration
AEROBIC GLYCOLYSIS AND THE ELECTRON TRANSPORT CHAIN


Illustration
KREBS CYCLE


Contents
1. Pyruvic acid from glycolysis is converted to acetyl coenzyme A (acetyl CoA).
2. Acetyl CoA enters the Krebs cycle and forms 2 ATP, carbon dioxide, and hydrogen.
3. Hydrogen in the cell combines with two coenzymes that carry it to the electron transport chain.
Oxidation of Carbohydrate
4. Electron transport chain recombines hydrogen atoms to produce ATP and water.
5. One molecule of glycogen can generate up to 39 molecules of ATP.

Illustration
OXIDATIVE PHOSPHORYLATION
¯

Contents
Oxidation of Fat
w Lypolysis—breakdown of triglycerides into glycerol and free fatty acids (FFAs).
w FFAs travel via blood to muscle fibers and are broken down by enzymes in the mitochondria into
acetic acid which is converted to acetyl CoA.
w Aceytl CoA enters the Krebs cycle and the electron transport chain.
w Fat oxidation requires more oxygen and generates more energy than carbohydrate oxidation.

Tables 2 tiff
Energy Production From the Oxidation
of Liver Glycogen
Glycolysis (glucose to pyruvic acid) 3 4-6b
Pyruvic acid to acetyl coenzyme A 0 6
Krebs cycle 2 22
Subtotal 5 32-34
By oxidative
 Stage of process Direct phosphorylationa
aRefers to adenosine triphosphate (ATP) produced by transferring H+ and electrons to the electron
transport chain. bThe energy yield differs depending on whether reduced nicotinamide adenine
dinucleotide (NADH) or reduced flavin adenine dinucleotide (FADH) is the carrier molecule to
transport the electron through the mitochondrial membrane and the electron transport chain, with
NADH yielding up to 39 molecules of a ATP and FADH yielding 37 molecules of ATP.
Total 37-39

Illustration
METABOLISM OF FAT


Tables 2 tiff
Energy Production From the Oxidation
of Palmitic Acid (C16H32O2)
Fatty acid activation 0 –2
b-oxidation 0 35
Krebs cycle 8 88
Subtotal 8 121
By oxidative
  Stage of process Direct phosphorylation
Total 129
Adenosine triphosphate produced from 1 molecule
of palmitic acid

Contents
Protein Metabolism
w Body uses little protein during rest and exercise
(less than 5% to 10%).
w Some amino acids that form proteins can be converted
into glucose.
w The nitrogen in amino acids (which cannot be oxidized) makes the energy yield of protein
difficult to determine.

Výsledek obrázku pro energy systems in sport and exercise



Illustration
INTERACTION OF ENERGY SYSTEMS ILLUSTRATING THE PREDOMINANT ENERGY SYSTEM
Výsledek obrázku pro Anaerobic and aerobic energy requirements for different sports







Contents
What Determines Oxidative Capacity?
w Oxidative enzyme activity within the muscle
w Fiber-type composition and number of mitochondria
w Endurance training
w Oxygen availability and uptake in the lungs
Arm

Contents
Measuring Energy Costs of Exercise
Direct calorimetry—measures the body's heat production to calculate energy expenditure.
Sciencelab1
Indirect calorimetry—calculates energy expenditure from the respiratory exchange ratio (RER) of
VCO2 and VO2.
.
.

Illustration
CALORIMETRIC CHAMBER


Illustration
MEASURING RESPIRATORY GAS EXCHANGE


Contents
Respiratory Exchange Ratio
w The RER value at rest is usually 0.78 to 0.80
w The ratio between CO2 released (VCO2) and oxygen consumed (VO2)
.
.
w RER = VCO2/VO2
.
.
Treadmill
w The RER value can be used to determine energy substrate used at rest and during exercise, with a
value of 1.00 indicating CHO and 0.70 indicating fat.

Tables 2 tiff
Caloric Equivalence of the Respiratory Exchange Ratio (RER) and % kcal From Carbohydrates and Fats
0.71 4.69 0.0 100.0
0.75 4.74 15.6 84.4
0.80 4.80 33.4 66.6
0.85 4.86 50.7 49.3
0.90 4.92 67.5 32.5
0.95 4.99 84.0 16.0
1.00 5.05 100.0 0.0
RER kcal/L O2 Carbohydrates Fats
Energy % kcal

Contents
Metabolic Rate
w Rate at which the body expends energy at rest and
during exercise
w Measured as whole-body oxygen consumption and
its caloric equivalent
w The minimum energy required for normal daily activity is about 1,800 to 3,000 kcal/24 hr
Kilowattmeter
w Basal or resting metabolic rate (BMR) is the minimum energy required for essential physiological
function
(varies between 1,200 and 2,400 kcal/24 hr)

Contents
Factors Affecting BMR/RMR
w The more fat-free mass, the higher the BMR
w The more body surface area, the higher the BMR
w BMR gradually decreases with increasing age
w BMR increases with increasing body temperature
w The more stress, the higher the BMR
w The higher the levels of thyroxine and epinephrine,
the higher the BMR

Contents
Caloric Equivalents
w Food energy equivalents
CHO: 4.1 kcal/g
Fat: 9.4 kcal/g
Protein: 4.1 kcal/g
w Energy per liter of oxygen consumed
CHO: 5.0 kcal/L
Fat: 4.7 kcal/L
Protein: 4.5 kcal/L
Example: VO2 rest = 0.300 L/min ´ 60 min/hr ´ 24 hr/day = 432 L/day ´ 4.8 kcal/L = 2,074 kcal/day
.

Contents
Factors Influencing Energy Costs
w Type of activity
w Activity level
w Sex
w Age
w Size, weight, and body composition
w Intensity of the activity
w Efficiency of movement
w Duration of the activity
Boyskateboarding

Illustration
USE OF MUSCLE GLYCOGEN DURING EXERCISE


Illustration
GLYCOGEN USE DURING RUNNING


Mean Energy expenditure (EE) per day in kJ.
Female (20 – 30 years old)
Height
Weight
No activity
Medium activity
High activity
160 cm
50 kg
7500
8600
9100
60 kg
8200
9200
10100
170 cm
60 kg
8200
9200
10100
70 kg
8900
10000
11100
180 cm
70 kg
8900
10000
11000
80 kg
9600
10800
12100

Mean Energy expenditure (EE) per day in kJ.
Male (20-30 years old)
Height
Weight
No activity
Medium activity
High activity
170 cm
60 kg
9800
10800
11800
70 kg
10500
11500
12500
180 cm
70 kg
10500
11500
12500
80 kg
11300
12400
13500
190 cm
80 kg
11300
12400
13500
90 kg
12200
13000
14100

Guidelines for conditions of resting measurements
The Academy of Nutrition and Dietetics (AND) :
In preparation, a subject should be fasting for 7 hrs or greater, and mindful to avoid stimulants
and stressors, such as caffeine, nicotine, and hard physical activities such as purposeful
exercises.
For 30 minutes before conducting the measurement, a subject should be laying supine without
physical movements, no reading nor listening to music. The ambiance should reduce stimulation by
maintaining constant quiet, low lighting, and steady temperature. These conditions continue during
the measurement stage.
Indirect calorimetry is considered the gold-standard method to measure RMR.

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