Measuring Energy Expenditure

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Measuring Energy Expenditure
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Introduction

• ATP provides energy
• Part of that energy is lost as heat

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Measuring the Energy Costs of Exercise
Direct calorimetrymeasures the body's heat
production to calculate energy expenditure.
Indirect calorimetrycalculates energy
expenditure from the respiratory exchange ratio
(RER) of CO2 and O2.
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A CALORIMETRIC CHAMBER
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INDIRECT CALORIMETRY
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Indirect Calorimetry

• Aerobic energy only
• Indirect calorimetry measures O2 (VO2) which is
  converted into calories.
• Also, requires the measurement of fuel
  utilization or RQ
• RQ is measured at the cell
• R or RER is measured at the mouth

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What is the relationship between the amount of
oxygen used (VO2) and the amount of ATP made by
the body?
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What is VO2
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(No Transcript)
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Oxygen Consumption (VO2)

• Measurements
• Ventilation rate
• O2
• CO2
• Units
• ml/kg/min
• Liters/min

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Oxygen Consumption (VO2)
79 N 20.97 O2 0.03 CO2
Ventilation (Liters of air per minute)
79 N Less O2 More CO2
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Oxygen Consumption (VO2)

• VO2 VE (FIO2 FEO2)
• VE is the rate at which air is exhaled in liters
  per minute
• FIO2 FEO2 accounts for the amount of O2 removed
  from the blood (or consumed for aerobic energy
  production)
• Therefore, VO2 the rate at which oxygen is
  consumed per minute.

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VO2 values

• At rest, VO2 3.5 ml/kg/min
• During exercise the amount of oxygen used by the
  body will increase so VO2 will increase
• The highest obtainable VO2 level during maximal
  exercise is called VO2max.

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VO2max

• Leveling off of VO2, despite and increase in
  workload
• Post-exercise blood lactate greater than 8
  mmol/liter
• R greater than 1.15
• Test length 8-12 minutes

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VO2max (ml/kg/min) - ACSM
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What is VCO2?
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VCO2 values

• Not enough people care.

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What is R?

• Indicator of fuel utilization
• Also know as
• RER estimated from indirect calorimetry
• RQ measured at the cell

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Respiratory Quotient

• C6 H12 O6 6 O2 ? 6 CO2 6 H2O
• 6 CO2 / 6 O2 1.0
• C57 H104 O6 80 O2 ? 57 CO2 52 H2O
• 57 CO2 / 80 O2 0.7

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Respiratory Exchange Ratio
w The RER value will be between 0.7 and 1.0
w The RER value at rest is usually 0.78 to 0.80
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What can we learn from the RER value?

• The amount of carbohydrate and fat being burned
  during exercise
• To burn carbohydrates, the VCO2 6 and the VO2
  6
• The RER is, therefore, 6/6 or 1.0
• Fats require more O2 to be burned.
• To burn fats, the VCO2 16 and the VO2 23.
• The RER is, therefore, 16/23 or 0.7

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Metabolic Equivalents of O2 for Given RQ Values
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Advantages of Calorimetry

• Accurate estimations of energy requirements.
  (Table 4-3)
• Accurate estimations of fuel utilization.
• Assessment of cardiopulmonary function. (next
  slide)

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Key Topics

• The relationship between energy production (from
  carbohydrates and fats), VO2 and caloric
  expenditure