AnAerobic Metabolism During Exercise

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• Chapter 4

(An)Aerobic Metabolism During Exercise
Exercise Metabolism
EXERCISE PHYSIOLOGY Theory Application to
Fitness and Performance S. Powers E. Howley
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Metabolic Responses to Exercise What we know!

• Exercise poses a serious challenge to the
  bioenergetic pathways in working muscle
• Contracting skeletal muscle may increase their
  energy utilization 200 times over that at rest
• During heavy exercise, total energy expenditure
  may increase 15-25 times above rest
• At rest, almost 100 of the energy required to
  sustain bodily functions is produced by aerobic
  metabolism.

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Metabolic Responses to Exercise Influence of
Duration and Intensity

• Immediate pathway (1-10 sec)
• ATP-PC System
• Short-term pathway (10-60 sec)
• Anaerobic glycolysis Lactic Acid system
• Combo of ATP-PC, glycolysis aerobic systems (60
  sec - 2 min)
• Long-term pathway (gt2 min)
• Aerobic metabolism oxidative phosphorylation

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The Energy Continuum
Figure 4.1
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Interaction between the energy systems ATP
Production

• No exercise or event or physical activity is
  absolutely, purely, or solely anaerobic or
  aerobic
• Combination of immediate, anaerobic and aerobic
  one just dominates
• Anaerobic contribution is greater during short
  term, high intensity activity
• Aerobic contribution is greater during long term,
  lower to moderate intensity

Goucester 2008
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Figure 4.2
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Maximal Oxygen Uptake (VO2max)

• The maximal capacity to consume, transport, and
  utilize oxygen (expressed in absolute or relative
  terms)
• L/min ml/min ml/kg/min
• Measured by graded or incremental exercise tests
• Reached when increase in power output does not
  result in an increase in oxygen uptake
  (plateau)
• Genetics and training influences
• Physiological ceiling

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Lactate Production
Amount produced depends on 1. Muscle
contraction 2. Enzyme activity 3.
Muscle fiber type 4. SNS activation 5.
Insufficient oxygen
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Lactate Clearance 1. Oxidation
(intracellular) 2. Gluconeogenesis
(extracellular)
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Lactate Threshold

• As exercise intensity increases, blood levels of
  lactic acid HLa begin to rise in an exponential
  fashion
• Sudden rise in blood lactic acid level is point
  at which there is an increased reliance on
  anaerobic metabolism
• Occurs at 50-60 of VO2max in untrained Occurs
  at 65-85 of VO2max in trained
• Controversy re the terminology and the mechanism
  to explain the sudden rise in HLa

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Why is Lactic Acid a Problem? 1. Pain 2.
Performance decrement a. Metabolic
fatigue b. Muscular fatigue
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Figure 4.17
Figure 4.16
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The Exercise Response

• At the onset of exercise, VO2 increases rapidly
  until a steady state is reached
• VO2 does not instantaneously increase to S.S.
  level
• Oxygen Deficit - The difference between the
  oxygen required during exercise and the oxygen
  supplied and utilized. Occurs at the onset of
  all activity
• Oxygen Drift Rise in O2 consumption during
  moderate-heavy, submaximal exercise
• Excess Post Exercise Oxygen Consumption (EPOC)
  O2 consumption during recovery that is above
  normal resting values
• 1. Rapid portion (first 2-3 min post
  exercise)
• 2. Slow portion (persists gt 30 min post
  exercise)

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O2 deficit debt during light/moderate exercise
and heavy exercise
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Factors contributing to oxygen deficit
During the transition from rest-to-exercise (O2
deficit), energy is supplied by 1. The
splitting of stored ATP-PC 2. Anaerobic
glycolysis, with the concomitant production
of lactic acid 3. Utilization of oxygen stores
in capillary blood and on myoglobin 4.
Oxygen transport and utilization
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Exercise Response

• What variables do we need to assess aerobic
  capacity (submax maximal VO2, LT)?
• Oxygen Consumption (VO2) - The amount of oxygen
  taken up, transported and used at the cellular
  level
• Carbon Dioxide Produced (VCO2) -The amount of
  carbon dioxide generated during metabolism
• Lactate Threshold

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Factors governing fuel selection
Total contribution of protein 5-15, thus fat
and CHO serve as primary substrates Several
factors determining whether fat or CHO is the
primary substrate Diet Intensity (low vs.
high) Duration (short vs. prolonged)
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Exercise Intensity and Fuel Selection
As exercise intensity increases, there is an
exercise intensity at which the energy derived
from CHO exceeds that of fat This work rate has
been labeled the crossover point
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• Causes of this substrate shift?
• Recruitment of fast twitch fibers
• Better equipped to metabolize CHO than fats
  (enzymes)
• Increasing blood levels of Epinephrine
• High levels of EPI increase muscle glycogen
  breakdown, CHO metabolism, lactate production
• Increased lactate gt inhibition of fat metabolism

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Exercise Duration and Fuel Selection
As duration of submaximal exercise increases,
there is a gradual shift from CHO to fat
utilization
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Exercise Duration and Fuel Selection

• Why is there a gradual shift from CHO to fat
  utilization?
• Glycogen depletion
• Prolonged exercise gt rise in hormones gt
  stimulation of lipases gt lipolysis gt increase
  in blood and muscle levels of FFA gt promotion of
  fat metabolism

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The Aerobic Response to Exercise - Terminology
Caloric Cost - Energy expenditure of an activity
performed for a specific period of time
The Metabolic Equivalent (MET) - A unit that
represents the metabolic equivalent in multiples
of resting rate oxygen consumption of any given
activity 1MET 3.5 mlO2/kg/min 1MET
1kcal/kg/hr
Caloric Equivalent - The number of kilocalories
produced per liter of oxygen consumed
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F
uel Utilization During Exercise
Nutrient Kcal/gram Kcal/LO2 Carbohydrate
4.2 5.05 Protein 4.2
4.50 Fat 9.5 4.70
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Fuel Utilization During Exercise
To estimate the contribution of CHO or fat
metabolism during rest and/or exercise RQ - The
ratio of the amount of carbon dioxide produced
divided by the amount of oxygen consumed at the
cellular level RER (R) - O2 and CO2 exchange
measured at the lungs RER
CO2/O2
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Estimation of Fuel Utilization
Fat and CHO differ in the amount of O2 used and
CO2 produced during oxidation Fat VCO2 / VO2
16 CO2 / 23 O2 0.70 CHO VCO2 / VO2 6 CO2 /
6 O2 1.0 Fat 0.70 CHO 1.0 mixed 0.85
Fat oxidation requires more O2 than does CHO
oxidation.
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S
ummary of Aerobic Response
Caloric cost (kcal/min) O2 consumed (L/min) x
caloric equivalent (kcal/LO2) Example/Given RER
.91 O2 consumption 2.15 L/min Now calculate
caloric cost for 30 min of exercise
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S
ummary of Aerobic Response
O2 Consumed (L/min) x Caloric Equivalent O2
consumption 2.15 L/min Kcal/LO2 for .91
4.936 4.936 x 2.15 10.6 kcal/min x 30 318
kcal Multiply by to determine fat/CHO 318 x
0.694 220 Kcal from CHO 318 x 0.306 97 Kcal
from Fat
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