Transcript Metabolic System and Exercise

Metabolic System and Exercise
(continued)
EXS 558
Lecture #5
September 28, 2005
Review Questions #1
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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
Review Question #2
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One mole of ATP stores ~12,000 calories of
energy, BUT what is the true function of ATP?
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The true function of ATP is for the TRANSFER of energy
Review Question #3
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How quickly is your phosphocreatine (PC)
stores depleted within your body during
intense activity (sprinting)? Discuss the
timing of PC resynthesis.
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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
Review Question #4
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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
Review Questions #5, 6
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TRUE/FALSE
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Glycolysis, the breakdown of sugar, can be either
aerobic or anaerobic
TRUE/FALSE
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Glycolysis results in the production of 3 ATP
Review Question #7, 8
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What is the consequence if glycolysis
proceeds without the presence of oxygen?
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
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And if oxygen is present?
If oxygen is present then pyruvate is converted into acetyl-CoA
and then integrated within Krebs Cycle.
Review Question #9
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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
Review Question #10
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What is the effect of high intensity training to
the ATP-PC energy system?
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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
Metabolic System and Exercise
Adaptations – Endurance Effect
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Capillary Density
Myoglobin Content
Mitochondrial Function and Content
Oxidative Enzymes
Glycolytic Enzymes (?)
Results in 2-fold ↑ in capacities to oxidize sugar and fat
Metabolic Adaptation to Endurance
Training
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Capillary Density
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Endurance trained athletes 5-10% higher than
compared to sedentary controls
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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
Myoglobin Content
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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
Mitochondrial Function and Content
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Endurance training ↑ the size and # of
mitochondria
(Holloszy and Coyle, 1984)
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Size increased 35% during a 27 week
endurance training program in rats
Oxidative Enzymes
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↑ concentration of enzymes associated with
(1) Kreb’s Cycle, (2) electron transport chain,
(3) activation, transport and β-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)
Oxidative Enzymes (continued)
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Succinate dehydrogenase (SDH) enzyme
increases may be seen during the early
phases of a training program (2x)
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Plateau effect with a prolonged training program (after 4
months)
Poor correlation with maximal aerobic
capacity (VO2 max)
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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
SDH Effect
PLATEAU
Glycolytic Enzymes
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Endurance training has NO effect on
influencing [ ] of glycolytic enzymes
Effects of Detraining on Metabolic Enzymes
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Rats: 15 weeks of endurance training results in twofold ↑ in
cytochrome c, cistrase synthase and CoA transferase
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After training stops, all enzyme activities return to baseline within 4-5
weeks
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Humans: ↑ aerobic enzyme activity observed following 8-12
weeks endurance training, are returned to baseline within 6
weeks
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Rate of detraining depends on duration of training program
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Human subjects who had trained for 6-20 years, asked to suspend
training for 12 weeks
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Show significant in ↓ aerobic enzyme activity, but still 50% greater
than sedentary controls
Circulating Lipid Use During Exercise
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At rest plasma [FFA] 0.3 ≈ mmol/L
↓ in plasma [FFA] at onset of exercise,
followed by progressive ↑ as exercise
continues (>20 min)
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Initial ↓ in plasma [FFA] caused by imbalance
between uptake and release
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↑ Blood flow to muscle
Delay in lipolysis in adipocytes
Lipid Energy Sources During Exercise
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Plasma chylomicrons  minimal
Plasma VLDLs  minimal
Plasma FFAs  major source (from adipose), greatest
reliance at low to moderate intensity (25-50% VO2 max)
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Muscle FFAs  major source, used increasingly as
intensity exceeds 50% VO2 max
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At high intensity (90% VO2 max) CHO used as primary energy source
Reliance Upon Lipids vs. CHO During Exercise
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INTENSITY determines reliance upon fats as
energy substrate
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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 < 25%
Crossover Concept
Training
NO lactic acid buildup b/c of fat metabolism…good for athletes!
Causes for ↓ Fat Reliance at ↑ Intensities
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↓ circulating FFA levels
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↓ 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!
Glycogen Sparing Effect
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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
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True of absolute work load OR relative work intensity
Endurance athletes use fats more effeciently at
intensities > 50% VO2 max
Runners derive up to 75% of energy from fat when
working at 70% VO2 max
Glycogen Sparing Effect (continued)
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How does training allow greater reliance of
fats and less on CHO? Mechanisms include:
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↑ 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)
Glyocogen Sparing Effect (continued)
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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
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After training
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TG deposits in muscle twice as great
– Intramuscular TG depletion twice as great
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↑ use of intramuscular TG accounts for nearly all of
“Glycogen Sparing Effect”
Respiratory Exchange Ratio (RER)
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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
RER (continued)
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Indirect Calorimetry
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Assumes
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the body’s O2 content
remains constant
CO2 exchange in the
lung proportional to its
release from cells
Fats = 0.71
CHO = 1.00
RESEARCH REVIEW
Substrate Oxidation, Obesity and Exercise Training
Blank & Saris (2002)
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
Factors Influencing Energy Costs
w Type of activity
w Size, weight, and body composition
w Activity level
w Intensity of the activity
w Age
w Duration of the activity
w Sex
w Efficiency of movement
Muscle Glycogen & Exercise
Glyocogen During Running
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.
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.