Metabolic System and Exercise continued

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Metabolic System and Exercise(continued)

• EXS 558
• Lecture 5
• September 28, 2005

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Review Questions 1

• Which of the following is NOT an energy system
  used by the body to power physical activity?
• a.) glycolytic energy system
• b.) cytoplasmic energy system
• c.) oxidative energy system
• d.) phosphagen energy system

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Review Question 2

• One mole of ATP stores 12,000 calories of
  energy, BUT what is the true function of ATP?
• The true function of ATP is for the TRANSFER of
  energy

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Review Question 3

• How quickly is your phosphocreatine (PC) stores
  depleted within your body during intense activity
  (sprinting)? Discuss the timing of PC
  resynthesis.
• PC stores are depleted in 30 seconds and ½ of the
  PC stores can be recovered in 20-30 seconds but
  the remaining ½ may take up to 20 minutes to
  fully restore. Most, however, is restored within
  3 minutes

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Review Question 4

• Which if the following is the process by which
  glycogen is synthesized from glucose to be stored
  in the liver?
• a.) glycolysis
• b.) glycogenesis
• c.) glycogenolysis
• d.) glucolysis

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Review Questions 5, 6

• TRUE/FALSE
• Glycolysis, the breakdown of sugar, can be either
  aerobic or anaerobic

• TRUE/FALSE
• Glycolysis results in the production of 3 ATP

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Review Question 7, 8

• What is the consequence if glycolysis proceeds
  without the presence of oxygen?
• And if oxygen is present?

The byproduct is lactic acid which can accumulate
in the cell, and (1) interfere with the
production of ATP and (2) hinder the binding of
calcium to troponin
If oxygen is present then pyruvate is converted
into acetyl-CoA and then integrated within Krebs
Cycle.
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Review Question 9

• Oxidative capacity is determined by all of the
  following except?
• a.) enduance training
• b.) fiber-type composition and of mitochondria
• c.) oxygen availability and uptake in lungs
• d.) phosphocreatine concentration

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Review Question 10

• What is the effect of high intensity training to
  the ATP-PC energy system?
• No effect to the resting PC levels, but the
  activity of glycolytic enzymes can potentially be
  increased thus improving the efficiency of the
  energy system

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Metabolic System and Exercise Adaptations
Endurance Effect

• Capillary Density
• Myoglobin Content
• Mitochondrial Function and Content
• Oxidative Enzymes
• Glycolytic Enzymes (?)

Results in 2-fold ? in capacities to oxidize
sugar and fat
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Metabolic Adaptation to Endurance Training

• Capillary Density
• Endurance trained athletes 5-10 higher than
  compared to sedentary controls
• Genetic predisposition?
• Not really, a 15 ? in capillary content of
  skeletal muscle
• Changes occur in a few weeks to months after an
  endurance program has started
• Increase exchange of gases, heat, waste, and
  nutrients between muscle and blood

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Myoglobin Content

• Myoglobin oxygen transport and storage protein
  of blood
• Transfers oxygen from capillaries to the
  mitochondria
• Animal studies have shown ? myoglobin content but
  human studies do not corroborate
• Role of myglobin in improving aerobic capactiy in
  humans remains unclear

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Mitochondrial Function and Content

• Endurance training ? the size and of
  mitochondria (Holloszy and Coyle, 1984)
• Size increased 35 during a 27 week endurance
  training program in rats

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Oxidative Enzymes

• ? concentration of enzymes associated with (1)
  Krebs Cycle, (2) electron transport chain, (3)
  activation, transport and ß-oxidation of FFA
• Better efficiency spares muscle glycogen and
  prevents buildup of lactic acid
• Enzyme buildups increase at a greater rate in
  type II oxidative fibers (FOG)

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Oxidative Enzymes (continued)

• Succinate dehydrogenase (SDH) enzyme increases
  may be seen during the early phases of a training
  program (2x)
• Plateau effect with a prolonged training program
  (after 4 months)
• Poor correlation with maximal aerobic capacity
  (VO2 max)
• Suggests that other factors may have a greater
  influence on improving aerobic capacity

? Oxidative enzyme concentrations may allow
athletes to exercise at higher intensity than
improving aerobic capactiy
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SDH Effect
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Glycolytic Enzymes

• Endurance training has NO effect on influencing
  of glycolytic enzymes

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Effects of Detraining on Metabolic Enzymes

• Rats 15 weeks of endurance training results in
  twofold ? in cytochrome c, cistrase synthase and
  CoA transferase
• After training stops, all enzyme activities
  return to baseline within 4-5 weeks
• Humans ? aerobic enzyme activity observed
  following 8-12 weeks endurance training, are
  returned to baseline within 6 weeks
• Rate of detraining depends on duration of
  training program
• Human subjects who had trained for 6-20 years,
  asked to suspend training for 12 weeks
• Show significant in ? aerobic enzyme activity,
  but still 50 greater than sedentary controls

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Circulating Lipid Use During Exercise

• At rest plasma FFA 0.3 mmol/L
• ? in plasma FFA at onset of exercise, followed
  by progressive ? as exercise continues (gt20 min)
• Initial ? in plasma FFA caused by imbalance
  between uptake and release
• ? Blood flow to muscle
• Delay in lipolysis in adipocytes

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Lipid Energy Sources During Exercise

• Plasma chylomicrons ? minimal
• Plasma VLDLs ? minimal
• Plasma FFAs ? major source (from adipose),
  greatest reliance at low to moderate intensity
  (25-50 VO2 max)
• Muscle FFAs ? major source, used increasingly as
  intensity exceeds 50 VO2 max
• At high intensity (90 VO2 max) CHO used as
  primary energy source

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Reliance Upon Lipids vs. CHO During Exercise

• INTENSITY determines reliance upon fats as energy
  substrate
• Low to moderate intensity (25-50 VO2 max)
  50-70 energy supplied by fats, 5 by proteins,
  rest by CHO
• 60-65 and above VO2 max, reliance upon lipids
  generally ? while CHO reliance gradually ?
• At intensity of 85 VO2 max lipid contribution lt
  25

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Crossover Concept
NO lactic acid buildup b/c of fat metabolismgood
for athletes!
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Causes for ? Fat Reliance at ? Intensities

• ? circulating FFA levels
• ? rate FFA release from adipocytes (inhibited by
  acidosis)
• Inadequate transport of albumin
• ? rate of lipolysis of intramuscular TG stores
• ? uptake of circulating FFAs by muscle
• TRAINING can alter these!

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Glycogen Sparing Effect

• Training has no effect on total amount of energy
  required to perform a specific task
• Training does allow greater reliance on fats to
  provide that energy
• True of absolute work load OR relative work
  intensity
• Endurance athletes use fats more effeciently at
  intensities gt 50 VO2 max
• Runners derive up to 75 of energy from fat when
  working at 70 VO2 max

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Glycogen Sparing Effect (continued)

• How does training allow greater reliance of fats
  and less on CHO? Mechanisms include
• ? Mito density, ? oxidative enzyme capacity
• ? Capillary density (? oxygen delivery)
• Smaller changes in ATP and ADP
• ? Stimulation of hexokinase, PFK, and
  phosphorylase
• Maintain normal citrate levels more efficiently
• ? sensitivity of adipose to epinephrine (?
  lipolysis)

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Glyocogen Sparing Effect (continued)

• Appears that ? reliance upon fat directly related
  to ? use of intramuscular stores of triglycerides
  (TG)
• Compare human subjects before and after 12 weeks
  endurance training program
• After training
• TG deposits in muscle twice as great
• Intramuscular TG depletion twice as great
• ? use of intramuscular TG accounts for nearly all
  of Glycogen Sparing Effect

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Respiratory Exchange Ratio (RER)

• Used to measure the type of food source being
  metabolized to produce energy
• RER (V CO2)/ (V O2)
• The carbon and oxygen contents of glucose, FFAs
  and amino acids differ

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RER (continued)

• Indirect Calorimetry
• Assumes
• the bodys O2 content remains constant
• CO2 exchange in the lung proportional to its
  release from cells
• Fats 0.71
• CHO 1.00

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RESEARCH REVIEWSubstrate Oxidation, Obesity and
Exercise TrainingBlank Saris (2002)
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Fatigue and its Causes
w Phosphocreatine (PCr) depletion
w Glycogen depletion (especially in activities
lasting longer than 30 minutes)
w Accumulation of lactate and H (especially in
events shorter than 30 minutes)
w Neuromuscular fatigue
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Factors Influencing Energy Costs
w Size, weight, and body composition
w Type of activity
w Intensity of the activity
w Activity level
w Duration of the activity
w Age
w Efficiency of movement
w Sex
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Muscle Glycogen Exercise
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Glyocogen During Running
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Metabolic By-Products and Fatigue
w Short duration activities depend on anaerobic
glycolysis and produce lactate and H.
w Cells buffer H with bicarbonate (HCO3) to keep
cell pH between 6.4 and 7.1.
w Intercellular pH lower than 6.9, however, slows
glycolysis and ATP production.
w When pH reaches 6.4, H levels stop any
further glycolysis and result in exhaustion.
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Fatigue and Its Causes
w Fatigue may result from a depletion of PC or
glycogen, which then impairs ATP production.
w The H generated by lactic acid causes fatigue
in that it decreases muscle pH and impairs the
cellular processes of energy production and
muscle contraction.
w Failure of neural transmission may cause some
fatigue.
w The central nervous system may also perceive
fatigue as a protective mechanism.
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