Metabolic System and Exercise
EXS 558
Lecture #4
September 21, 2005
Review Questions #1-3

What is the primary role of hormones?


Most hormone secretion is modulated
through what biological process?


Maintain homeostasis
Negative Feedback
Why is this process effective?

Self-limiting
Review Question #4

Name three mechanisms which affect
circulating concentrations of hormones?
1.) exercise (physical stress)
2.) psychological stress
3.) fluid volume stress
Review Question #5

Exercise can induce alterations in the
endocrine system other than changing the
circulating concentrations of hormones. Give
an example of how this is possible.

Down-Regulation: the # of hormone receptors is
decreased to reduce the possibility of contact between
the “lock and key”
Review Question #6

What is one of the major differences between
steroid and peptide hormones?

Steroid hormones are lipid soluble allowing them to pass
through the cell membrane to their intracellular
receptors, while peptide hormones react with receptors
housed in the cell membrane
Review Questions #7, 8

TRUE/FALSE


A single training session has been shown to decrease
peripheral testosterone levels above resting levels
TRUE/FALE

Type of training program affects circulating testosterone
levels
Review Question #9

What would be the expected testosterone
response to a 10 mile run (~70 minutes)?
a.) no response, endurance activity has no effect
b.) ↑ circulating testosterone levels
c.) ↓ circulating testosterone levels
d.) first it increases and then decreases
Review Question #10

Which of the following has the LEAST effect
on influencing a growth hormone response?
a.) sleep
b.) nutrition
c.) exercise
d.) environment
Literature Review Techniques

SUNY Cortland Memorial Library Databases


http://library.cortland.edu/databases.asp
Search Options
1.) By Subject: Exercise Science & Sport Studies
a.) MEDLINE
b.) SportDiscus
c.) Physical Education Index
2.) Fulltext Database (.PDF available online)
Literature Review Techniques
(continued)
Find IT Button


Reference  Save Citation Information (APA)

Google Scholar
–

http://scholar.google.com/advanced_scholar_search
Cortland ESSS Librarian

hollistera@cortland.edu
Literature Review Techniques (continued)



Search for a recent REVIEW article close to
your topic, if possible
Print online abstracts of all articles you may
include within your review of literature
Use ILL early  it takes time to receive
articles
Metabolic System & Exercise
Aerobic vs. Anaerobic Training
Aerobic (endurance) training leads to
w Improved blood flow, and
w Increased capacity of muscle fibers to generate ATP
Metabolic and Morphological Changes
Anaerobic training leads to
w Increased muscular strength, and
w Increased tolerance for acid-base imbalances
during highly intense effort.
Metabolic Changes
Energy Systems

Phosphagen Energy System (ATP-PC)



Glycolytic Energy System



Cytoplasm
High-intensity: Up to 30 seconds
Cytoplasm
High-intensity: 1-3 minutes
Oxidative Energy System


Mitochondria
Activity > 3 minutes
ATP

Adenosine triphosphate (ATP) common currency of
useful (chemical) energy used by cells

Principle function of ATP
–
–
–
–
Energize synthesis of important cellular components
Energize muscular contractions
Synthesis of organic molecules used for structure and
function
Energize active transport
ATP (continued)

Energy released from ATP caused by
ATPase
ATP + water  ADP + Pi + 7,000 cals/mol
-
1 mole of energy of ATP stores
12,000 cals, however, the real
function of ATP is to transfer
energy!
- energy stored in ATP will sustain
life for about 90 seconds
ATP-PC Energy Source

ATP-PC (Phosphocreatine) stored within the muscle


PC is major storage depot for energy (13,000 cals/mol)


Immediate use
It transfers phosphate group to ADP, so it can become ATP again
Catabolic breakdown of food substrate leads to synthesis of
ATP

When subjects in study are brought to maximal exertion levels, ATP in
muscles has not dropped much, but PC levels are way down
ATP-PC Energy Source (continued)



PC supply exhausted in ~30 seconds
PC levels decline rapidly during intense
exercise (sprinting)
Resynthesis of PC




½ recovered in 20-30 seconds
Last ½ may take up to 20 minutes
Most replenished within 3 minutes
Implications for workout design
ATP and PC During Sprinting
Glucose 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
Breakdown of Sugar (Glycolysis)



10 step pathway leads to synthesis of 2
pyruvate molecules and net production of 2
ATP molecules (or 3)
All reactions in cytosol and none require O2
Fate of pyruvate depends on O2
–
–
If inadequate available (anaerobic), pyruvate
converted to lactate
If enough O2, converted to acetyl-CoA
Breakdown of Sugar (Glycolysis)

Where does the glucose come from?


From the blood (1) through CHO digestion or (2) from
the breakdown of glycogen in the liver
From glycogen broken down in the muscle

Gluconeogenesis = process of metabolizing glycogen
into glucose

Glycogen metabolized = 3 ATP
Glucose metabolized = 2 ATP

Role of Lactic Acid


Nociceptors (pain receptors) are sensitive to
changes in the cellular H+ levels
↑ lactic acid


interfere with production of ATP
Hinder binding of calcium to troponin (ECC)
*The combined actions of the ATP-PC 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.
Oxidative Energy Source
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
w Is the primary method of energy production during
endurance events
Oxidative Production of ATP
1. Aerobic glycolysis—cytoplasm
2. Krebs cycle—mitochondria (byproduct = CO2)
3. Electron transport chain—mitochondria
1 molecule  39 ATP
Oxidative energy system primarily uses CHO and FAT but during
periods of CHO and prolonged exercise significant amounts of
protein can be metabolized
Aerobic Glycolysis &
Electron Transport Chain
Krebs Cycle
Oxidation of Fat

Lipolysis = breakdown of fat for energy




triglycerides metabolized into glycerol and 3 free fatty
acids
Free fatty acids used as primary energy source
Free fatty acids enter the mitochondria and undergo βoxidation
Energy production from 1 molecule of fatty acid (palmitic
acid C16H32O2) yields 129 ATP
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.
Energy Source Interaction

ALL three sources will supply a portion of the
needed energy for exercise at all times

One system will predominate depending on the intensity of
the exercise
Oxidative Capacity

Determined by:




Oxidative enzyme activity within the muscles
Fiber-type composition and # of mitochondria
Oxygen availability and uptake in lungs
Endurance Training

What does training effect?
Review Ideas
w The ATP-PCr and glycolytic systems produce small
amounts of ATP anaerobically and are the major energy
contributors in the early minutes of high-intensity
exercise.
w The oxidative system uses oxygen and produces more
energy than the anaerobic systems.
w Carbohydrate oxidation involves glycolysis, the Krebs
cycle, and the electron transport chain to produce up to
39 ATP per molecule of glycogen aerobically.
(continued)
Review Ideas (continued)
w Fat oxidation involves b oxidation of free fatty acids, the
Krebs cycle, and the electron transport chain to produce
more ATP than carbohydrate, but it is O2-limited.
w Protein generally contributes little to energy production
(less than 5%), and its oxidation is complex because
amino acids contain nitrogen, which cannot be oxidized.
w The oxidative capacity of muscle fibers depends on their
oxidative enzyme levels, fiber-type composition, how they
have been trained, and oxygen availability.
Metabolic Adaptations to High Intensity Training

ATP-PC Energy System
–
–
No change to resting levels of ATP or PC
Resting [ ] of enzymes may be positively altered

Causes activity of ↑ creatine kinase and myokinase
–
–
ADP + ADP  ATP + AMP
 AMP leaves muscle and acts as signal to slow down glycolysis
Parra et al. (2000)

2 weeks of daily sprint training
–

↑ elevation of creatine kinase
6 weeks of daily sprint training with longer rest intervals
–
no change of creatine kinase
Metabolic Adaptations to High Intensity Training
(continued)

Glycolytic Energy System



↑ glyoclytic enzymes (10-25%)
Resistance training alone CAN NOT stimulate metabolic
changes
Implications
“These studies suggest that athletes training for anaerobic
sports need to include both resistance training and sprint
or interval exercises in their conditioning programs in
order to maximize their physiological adaptation for the
sport”
J. Hoffman
Metabolic Adaptations to High Intensity Training
(continued)

Oxidative Energy System

High intensity training ↑ mitochondrial enzyme activity
–


When duration of exercises exceeds 3 minutes
Does not match gains from endurance training
Implications

An athlete who trains anaerobically may still generate
some aerobic capacity improvements
Metabolic Adaptations to High Intensity Training
(continued)

Improvements to buffering capactiy
–
–
–
Allows greater [ ] of lactic acid before effecting
muscular output
↑ 12-50% from a 8 week high intensity training
program
↑ 9.6% of blood lactate after 6 weeks of high
intensity cycling program
(Jacobs et al., 1987)