Exercise Physiology

1
Exercise Physiology
Krishna Asundi, PhD Research Fellow Harvard
School of Public Health
2
Course Schedule

• March 3rd Bioenergetics and Exercise Metabolism
• Submit list of references (cite the sources
  appropriately APA writing style)
• March 10th Physiology of Training
• Submit abstract of paper
• March 31st Training for Performance
• April 7th Oral Presentations
• April 21st Oral Presentations
• May 9th Term paper deadline

3
Scientific Term Paper

• Abstract (5 points)
• Summarizes the central question principal
  findings and conclusions.
• Should spark the readers interest to continue
  reading the paper
• Primary research question (5 points)
• A focused question on a scientific topic
• Scientific Review (15 points)
• Comprehensive review of the literature focused on
  the topic
• Discussion/ Interpretation (25 points)
• What is known and what is uncertain?
• What conclusions can be drawn from the studies
  found in the literature
• What are the uncertainties/ confounding factors
• Writing (5 points)
• Clarity of exposition/ style
• Structure
• Annotation (5 points)
• Reference list
• Appropriate use, style and consistency of
  citations

4
Presentation

• Short 10 15 minutes (No more than 15 slides!)
• Focus on the most interesting study/studies from
  your term paper, dont try to cover everything
  you are writing about
• Provide enough background for people to
  understand the question
• Structure
• Research Question
• Background
• Question asked by Study of interest
• Results from the study of interest
• How do the results contribute to answering your
  question
• Remaining questions
• Conclusions

5
Review

• Muscles convert ATP energy into mechanical energy
• Muscle length and contraction speed affects force
  production
• Muscles contain fast and slow twitch fibers with
  different biochemical and contractile properties
• Fast fibers anaerobic energy system, fatigue
  quicker and produce more force
• Slow fibers aerobic energy system, resist
  fatigue, contract slower

6
Review

• The circulatory system transports gases (O2, CO2)
  and nutrients throughout the body
• Heart beat, stroke volume, and vasodilatation /
  vasoconstriction act to regulate blood flow
• Gas exchange between the blood and atmosphere
  occurs in the lungs
• Ventilation acts to regulate the rate of exchange

7
Todays Class

• How do cells convert carbohydrates, fats and
  proteins into ATP
• Aerobic vs. Anaerobic Respiration
• Maximal Oxygen Uptake (VO2 max)
• Metabolic Response to Exercise
• Fuel Selection during exercise

8
Bioenergetics
9
Bioenergetics

• Describes how energy is transformed in cells
• Molecules contain energy in the bonds that hold
  them together
• Reactions that form strong bonds (absorb energy)
  are called endergonic
• Reactions that break strong bonds (release
  energy) are called exergonic

10
Fuels for the body
11
Carbohydrates

• Yield approximately 4 kcal per gram
• Monosaccharide (glucose, fructose)
• Disaccharides (sucrose),
• Polysaccharides (starch, cellulose)
• Are stored in the body as glucose or glycogen
  (long chains of glucose)
• Breakdown of glycogen into glucose occurs in
  muscle cells and the liver
• Glucose and glycogen, stored in muscle cells and
  the liver, are depleted within a few hours during
  exercise

12
Fats

• Yield approximately 9 kcal of energy per gram
• Fatty acids
• Triglycerides (three fatty acids and one glycerol
  molecule)
• Phospholipids, Steroids
• Fatty acids are used by cells for energy
• Fatty acids are stored in the body as
  triglycerides
• Triglycerides are primarily stored in fat cells,
  but also found in skeletal muscle
• Phospholipids and steroids are not used as energy
  sources

13
Proteins

• Yield approximately 4 kcal of energy per gram
• Are a chain of several amino acids
• Proteins must be broken down into amino acids to
  be used to produce energy

14
Adenine Triphosphate

• ATP High energy phosphate compound
• Serves as the bodys universal energy donor
• Energy from food is converted into ATP which is
  then used for various cellular processes
• Three metabolic pathways to produce ATP

15
Energy Systems
16
ATP PC system

• Pathway by which phosphocreatine is used to
  generate ATP
• Simplest and fastest method of producing ATP
• Very short term, high intensity exercise
• 50m sprint, powerlift, high jump etc.
• Muscle cells only store small amounts of PC
• PC reformation requires ATP and only occurs
  during recovery from exercise

17
Glycolysis

• Breakdown of glucose into pyruvic acid or lactic
  acid
• Short term (less than 10 minutes), bursts of
  energy
• Basketball, football, volleyball
• 1 glucose molecule produces 2 molecules of
  pyruvate and 2 or 3 molecules of ATP
• If oxygen is available, pyruvic acid is used in
  oxidative phosphorylation
• If oxygen is not available, pyruvic acid is
  converted to lactic acid

18
Oxidative Phosphorylation

• Pathway by which energy in fatty acids, amino
  acids and pyruvate (from glycolysis) is used to
  generate ATP
• Occurs inside the mitochondria
• Three Steps
• 1) Substrates (fatty acids, amino acids,
  pyruvate) are converted to Acetyl-CoA
• 2) Krebs Cycle Acetyl-CoA is converted into
  several intermediaries. In this process electrons
  are shuttled to the Electron Transport Chain
• 3) Electron transport chain Electrons are
  transported through the membrane of the
  mitochondria. Electron movement creates a flow
  of H. Energy from this flow of H is used to
  generate ATP.
• O2 is required to accept the electrons from the
  last step of the transport chain

19
ATP Production

• ATP PC System
• 1 PC molecule generates 1 ATP molecule
• Glycolysis
• 1 glucose molecule produces 2 3 ATP molecules
• Oxidative Phosphorylation
• 1 glucose molecule produces 32 33 ATP molecules

20
Energy System Selection

• High intensity
• 2 20 seconds, ATP production dominated by
  ATP-PC system
• 20 45 seconds, dominated by glycolysis
• gt 45 seconds, a combination of the ATP PC,
  glycolysis and aerobic systems
• Lower intensity
• 10 minutes, 80 aerobic
• gt30 minutes, nearly all aerobic
• Recovery
• The aerobic energy system restores energy when
  intensity decreases

21
Energy System Selections

• During exercise a combination of systems are used
  to produce energy
• The rate of energy demand (power output) dictates
  how energy will be produced

From Powers Howley. (2007). Exercise
Physiology. McGraw-Hill.
22
Exercise Metabolism
23
Exercise Metabolism

• Describes the relationship between fuel
  use/selection, energy pathways and by-products
• The majority of the bodys energy needs are
  provided aerobically
• Anaerobic pathways typically supplement based on
  energy demands

24
Aerobic Energy

• During low intensity exercise, the majority of
  energy is provided aerobically
• Also, energy spent anaerobically is recovered
  aerobically (i.e. after a sprint)
• Energy produced aerobically requires O2
• Therefore, O2 uptake can be used as a measure for
  energy use

25
Oxygen Uptake (VO2)

• With incremental increases in work output, oxygen
  uptake increases linearly to a maximum
• VO2 max Maximal capacity of the body to
  transport and utilize oxygen during exercise

26
VO2 Max

• The respiratory and cardiovascular systems and
  muscle composition all affect a persons VO2 max
• A high VO2 max indicates a higher power output
  over an extended period of time
• It also indicates faster energy recovery
• Good for marathon runners, unimportant for power
  lifters
• What about football players?

27
Fuel Selection

• Carbohydrates and fats provide nearly all the
  energy during exercise
• Proteins contribute less than 2 to energy
  production during exercise
• Selection of carbohydrates or fats is determined
  by exercise intensity and duration

28
Fuel Selection
From Powers Howley. (2007). Exercise
Physiology. McGraw-Hill.

• As intensity increases carbohydrate use
  increases, fat use decreases
• As duration increase, fat use increases, carb use
  decreases

29
Optimal Fat Metabolism

• Two factors contribute to the rate of fat
  metabolism
• Rate of energy expenditure
• of energy that comes from fat
• This results in an optimal VO2 max for burning fat

From Powers Howley. (2007). Exercise
Physiology. McGraw-Hill.
30
Fuel Sources
31
Carbohydrates

• More than 80 are stored as glycogen in muscles
• About 15 are stored in the liver and released as
  glucose into the blood stream when needed
• About 5 are found in the blood and extracellular
  fluid as glucose

32
Fats

• The majority (gt96) of fat is stored as
  triglycerides in fat cells
• Triglycerides are also stored in muscle

33
Effects of Exercise Intensity

• Plasma FFA (fat from fat cells) is the primary
  fuel source for low intensity exercise
• As intensity increases, the source shifts to
  muscle glycogen

From Powers Howley. (2007). Exercise
Physiology. McGraw-Hill.
34
Effects of Exercise Duration
From Powers Howley. (2007). Exercise
Physiology. McGraw-Hill.

• As exercise continues, energy source switches
  from a mix to primarily plasma FFA and blood
  glucose

35
Review

• ATP is generated by three bioenergetic pathways
• ATP-PC
• Glycolysis
• Oxidative phosphorylation
• Pathway selection for energy depends on exercise
  intensity and duration
• Energy are primarily obtained from carbohydrates,
  fats or protein
• Steady state oxygen uptake can be used as a
  measure of work intensity (VO2)
• Fuel selection and fuel source are affected by
  exercise intensity and duration

36
Next Week

• Physiology of Training
• Effects of training on VO2 max
• Effects of training on performance and
  homeostasis
• Physiological effects of strength training