Exercise Metabolism

1
O2 Kinetics and EPOC
2
Acute adaptations to exercise

• Metabolic changes during exercise
• apply an understanding of the 3 energy systems
• phosphagen system
• glycolysis
• aerobic/mitochondrial respiration
• Rest to exercise transition
• VO2 or oxygen consumption (oxygen uptake)
• amount of oxygen consumed per minute (rate!)
• expressed as L/min, ml/min, ml/kg/min

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Rest-to-Exercise Transition

• Increase in VO2
• reaches steady state within 3-5 minutes
• condition where all metabolic demands are being
  met adequately
• ATP requirement is met through aerobic ATP
  regeneration
• state of ? mitochondrial respiration
• mitochondria can maintain cytosolic Redox
  Potential
• What is the Redox Potential?
• ratio of NAD/NADH
• shows state of cellular oxidizing power

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Rise in VO2 from start to S-S
energy requirement for steady-state!!
Training state and intensity of exercise can
affect the time to reach S-S!!
Why cant VO2 increase immediately to meet the
exercise demands?
Rise in VO2
5
Rise in VO2 effect of aerobic training
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Trained vs Untrained

• Mitochondria are stimulated faster to meet demand
• due to ? mitochondrial mass and oxidative enzyme
  activity
• reach S-S much faster
• mitochondria are stimulated by
• ADP and Pi
• Calcium
• ? Shuttling of cytosolic NADH into mitochondria
• Prior warm-up
• can also lower time to steady-state

7
VO2 Kinetics

• We can measure the rate of increase in VO2
• faster increase, better trained
• slower increase, less trained
• measure by the time constant (t0.5) or half-life
  variable
• The rise in VO2 to steady state is represented by
  a monoexponential equation

VO2 A (1 - e-Bx) E A magnitude of change, e
natural log base, B rate
constant, E beginning VO2, x time
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More trained, lower the t0.5Less trained,
higher the t0.5
VO2 A (1 - e-Bx) E A magnitude of change, e
natural log base, B
rate constant, E beginning VO2, x time
9
Effect of intensity on rest to S-S transition
The larger the increment, the longer the time to
steady state!
10
Note the inability to reach steady state
Note slow continued increase in VO2
Note the rapid increases in VO2
100 Watts
150 Watts
200 Watts
250 Watts
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Rest-to-Exercise Transition

• Oxygen deficit
• difference between O2 consumption demand
• lag in oxygen uptake to meet metabolic demands of
  exercise
• up to steady-state
• reflects ? anaerobic metabolism
• ? CP glycolysis to meet demands
• delay time for full mitochondrial contribution
• due to need for increased stimulation

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Oxygen Deficit
Greater the intensity, the greater the O2 deficit
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Response to Prolonged Exercise

• Exercise longer than 10 minutes
• ATP primarily from mitochondrial means
• Steady state exercise can be maintained
• Prolonged exercise in a hot/humid environment or
  at higher intensities
• Steady state not achieved
• Upward drift in VO2 over time

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VO2 Drift During Prolonged Exercise
For exercise intensities gt 60 VO2max
prolonged exercise (gt 30 min) causes a continued
increase in VO2 (due to increased temperature
and circulating catecholamines)
15
Exercise Duration and Fuel Selection

• During prolonged exercise
• shift from CHO toward fat metabolism
• Increased rate of lipolysis
• decreasing muscle glycogen stores
• gt 2 hrs with moderate to high intensity
• decreasing blood insulin levels
• can affect CNS function perception of effort

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CHO to Fat Shift - Prolonged Exercise
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Effect of Exercise Duration on Muscle Fuel Source
100
MuscleGlycogen
FFAUptake
80
60
Fuel Contribution( of total)
40
Blood GlucoseUptake
20
0
0
1
2
3
4
Time (hours)
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Recovery from exercise
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Recovery From Exercise

• Excess post-exercise oxygen consumption (EPOC)
• elevated VO2 for several min following exercise
• Very minimal increase above resting VO2
• dependent on exercise intensity duration
• most meaningful after high-intensity exercise
  less-trained individuals

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Recovery From Exercise

• Kcal expenditure following exercise
• 70-100 additional kcals
• little more than a piece of white bread!!
• Health and Fitness Industry
• tried to capitalize on EPOC for product sales
• bogus claims!!

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EPOC After Light Heavy Exercise
EPOC
EPOC
Class remember, EPOC can also be affected by
exercise duration!
22
Factors Contributing to EPOC
Restore glycogen stores
EPOC
CP
catecholamines
some converted to glucose
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Methods of Calorimetry
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CALORIMETRY
The science that quantifies the heat release
from metabolism (metabolic rate!).
Estimate!
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A CALORIMETRIC CHAMBER
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Calorimetry

• Direct Calorimetry
• direct measurement of heat in a chamber
• change in temp of water circulating through
  chamber
• body is good at storing heat (unreliable!)
• during exercise
• best for measuring BMR

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Calorimetry

• Indirect Calorimetry
• open-circuit method
• concerned with measuring VO2 during exercise
• quantify exercise intensity!!
• ratio of VO2 VCO2 to look at fuel substrate

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Open-circuit Indirect Calorimetry

• Fundamental Principles
• volume of oxygen consumed (VO2)
• equal to inspired - expired O2 volumes
• volume of carbon dioxide produced (VCO2)
• equal to expired - inspired CO2 volumes
• Lets calculate VO2!!!!

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Gas fractions in atmospheric air

• FIO2 (inspired fraction of oxygen)
• .2093
• FICO2 (inspired fraction of carbon dioxide)
• .0003
• FIN2 (inspired fraction of nitrogen)
• .7903

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Calculating VO2
VO2 VIO2 - VEO2
VO2 (VI ? FIO2) - (VE ? FEO2)
What is the FIO2 equal to???
.2093
What about FEO2???
depends!
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Calculating VO2
VO2 VIO2 - VEO2
VO2 (VI ? FIO2) - (VE ? FEO2)
Typically, we dont measure both VE VI!
We accomplish this through the Haldane
Transformation
We solve for VI using inspired and expired N2
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Haldane Transformation
VO2 VIO2 - VEO2
VO2 (VI ? FIO2) - (VE ? FEO2)
Volume of expired N2 is equal to inspired N2
We equate VI by assuming expired N2 is equal to
inspired N2
Fractions of expired N2 and inspired N2 differ
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Haldane Transformation
VO2 VIO2 - VEO2
VO2 (VI ? FIO2) - (VE ? FEO2)
FIN2 .7903
FEN2 1-(FEO2 FECO2)
VI VE ? (1 - FEO2 FECO2)
FIN2
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Calculating VO2
VO2 VIO2 - VEO2
VO2 (VI ? FIO2) - (VE ? FEO2)
- (VE ? FEO2)
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The non-protein caloric equivalents for RQ
(simplified)
Lusk (1928) removed caloric release of basal
protein catabolism able to better discern heat
release of CHO fat
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Non-protein RQ chart

• Limitations of chart
• not valid in states of ? protein catabolism
• ? duration intensity of exercise
• poor CHO diet
• hyperventilation

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RER vs RQ

• States where RER ? RQ
• Metabolic acidosis
• inflates VCO2
• Non-steady state exercise
• ? VO2 and a likelihood for an inflated VCO2
• Hyperventilation
• ? VCO2
• Prolonged exercise
• ? protein catabolism

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In Exercise Physiology
What is the caloric equivalent we typically use
to calculate caloric expenditure?
5 Kcals/L O2
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Energy expenditure from Indirect calorimetry

• Calculating energy expenditure
• have to know
• VO2
• RER
• RER caloric equivalent
• Exercise duration

For example, exercising at a VO2 1.5 L/min and
0.9 for 30 min kcal 1.5 (L/min) x 4.924
(kcal/L) x 30 (min) 221.6 kcal
Kcal VO2 (L/min) x RER caloric equivalent x
time (min)
kcal 1.5 (L/min) x 5 (kcal/L) x 30 (min)
225 kcal
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Exercising at a VO2 2.0 L/min VCO2 1.8 L/min
for 40 min kcal 2.0 (L/min) x 4.924 x 40
(min) 393.9 kcal