Measurement of metabolism (indirect calorimetry); Energy expenditure calculations

Energy Expenditure Calculations

• Focus on determining how much fat and carbohydrate are burned during various exercise scenarios.

• Refer to Chapter 4, "Exercise Metabolism," specifically page 93 for text discussion.

Bomb Calorimeter Components

• Components:

  • Thermometer

  • Lid

  • Stirrer

  • Water Sample (23.00 bath)

  • Temperature Reader

  • Stirring Motor

  • Fuse Wires

  • Wire

  • Ignition Box

  • Bomb Cell

Whole-room Calorimeter

• Overview and function not provided, but indicates an additional method for measuring calorimetry.

Measuring Oxygen Uptake and Carbon Dioxide Production

• Measuring VO2 and VCO2:

  • Measuring oxygen uptake (VO₂) and carbon dioxide production (VCO₂) is essential for calculating the Respiratory Quotient (RQ).

  • RQ and VO₂ can be used to calculate fuel utilization during exercise.

Indirect Calorimetry

• Components of the system:

  • Expired air

  • Subject being tested

  • Volume analyzer

  • Mixing chamber

  • O₂ analyzer

  • CO₂ analyzer

  • Computer

Example Calculation Using VO2 and RQ Table

Example 1: Carbohydrate Burn Rate Calculation

• Scenario: How long would it take to burn 200 grams of carbohydrate while exercising at a VO2 of 2.0 liters/min and an RQ of 0.86?

  • Assumptions: 4 kcal/gram for carbohydrate.

  • At RQ = 0.86, 2.64 kcal/L O₂ from carbohydrate is utilized.

  • VO₂ of 2.0 liters/min results in:

  • Energy burned = $(2.0 ext{ liters/min} imes 2.64 ext{ kcal/liter O₂}) = 5.28 ext{ kcal/min}$.

  • 200 grams of carbohydrate equals:

  • Energy = $(200 ext{ g} imes 4 ext{ kcal/g}) = 800 ext{ kcals}$.

  • Time to burn 800 kcals:

  • $(800 ext{ kcals} ext{ divided by } 5.28 ext{ kcal/min}) <br>ightarrow 151.5 ext{ min} <br>ightarrow 2 ext{ hours, } 32 ext{ min}$.

RQ Table for Carbohydrate and Fat Oxidation

• RQ Values:

  • Sequence of RQ values from 1.00 down to 0.70, displaying the corresponding VCO₂/VO₂, kcal/liter O₂ for both carbohydrate and fat, and the percentage of total kcal from each fuel source.

  • Example Row:

  • At RQ = 0.90:

    • $( ext{VCO₂/VO₂} = 4.92)$

    • $( ext{kcal/liter O₂ from carbohydrate} = 3.32, ext{kcal/liter O₂ from fat} = 1.60)$

    • % of total kcal from carbohydrate = 67.5%, from fat = 32.5%.

Solving Energy Expenditure Problems

• Steps:

  1. Determine the focus of the question (e.g., total kcals, carbohydrate, fat).

  2. Utilize the appropriate kcal/Liter O₂ consumed column based on the question type:

  • Total kcals: kcal/Liter O₂

  • Carbohydrate: kcal/Liter O₂ from carbohydrate

  • Fat: kcal/Liter O₂ from fat

  • Mixed questions: use both columns accordingly.

Example 2: Energy Expenditure Calculation

• Scenario: Calculate time to burn 400 grams of carbohydrate at VO2 of 2.5 L/min and RQ of 0.90.

  • For RQ = 0.90, $(3.32 ext{ kcal/L O₂})$ for carbohydrate.

  • Energy burned per minute = $(2.5 ext{ L/min} imes 3.32 ext{ kcal/L O₂}) = 8.3 ext{ kcal/min}$.

  • Total energy in 400 grams = $(400 ext{ g} imes 4 ext{ kcal/g}) = 1,600 ext{ kcals}$.

  • Time = $(1,600 ext{ kcals} ext{ divided by } 8.3 ext{ kcal/min}) <br>ightarrow 193 ext{ min}$.

Example 3: Fat Loss during Marathon

• Scenario: A woman runs 26.2 miles in 4 hours with an average VO₂ of 2.0 L/min and average RER (RQ) of 0.88.

  • For RQ = 0.88, $(1.92 ext{kcal/L O₂})$ for fat.

  • Energy burned per minute from fat: $(2.0 ext{ L/min} imes 1.92 ext{ kcal/L O₂}) = 3.84 ext{ kcal/min}$.

  • Total fat burned in 240 min = $(240 ext{ min} imes 3.84 ext{ kcal/min}) = 921.6 ext{ kcals}$.

  • Total fat mass loss = $(921.6 ext{ kcals} ext{ divided by } 9 ext{ kcal/g}) = 102.4 ext{ grams}$.

  • Fat burned per mile = $(102.4 ext{ g} ext{ divided by } 26.2) <br>ightarrow 3.9 ext{ grams/mile}$.

Example 4: Carbohydrate to Fat Ratio Calculation

• Scenario: A woman exercises at low intensity for 1 hour at VO₂ of 1.6 L/min with RQ of 0.84.

  • RQ = 0.84: 2.29 kcal/L O₂ for carbohydrate, 2.56 kcal/L O₂ for fat.

  • Carbohydrate grams burned/L O₂ = $( rac{2.29}{4}) <br>ightarrow 0.57 ext{ grams}$.

  • Fat grams burned/L O₂ = $( rac{2.56}{9}) <br>ightarrow 0.28 ext{ grams}$.

  • Ratio of carbohydrate to fat burned = $( rac{0.57}{0.28}) <br>ightarrow 2.04$.

Total Energy Expenditure Calculation

• Scenario: A woman exercises for 1 hour at VO₂ of 1.9 L/min with RQ of 0.87.

  • For RQ = 0.87, $(4.89 ext{kcal/L O₂})$.

  • Energy burned in 1 hour = $(1.9 ext{ L/min} imes 4.89 ext{ kcal/L O₂} imes 60 ext{ min}) = 557 ext{ kcals}$.

  • She consumes a pastry with 500 kcals.

  • Determination: The woman expended more kcals (557) than the kcal in the pastry (500).

Oxygen Consumption for Fat Burning

• Scenario: While exercising at a constant RQ of 0.80, calculate the liters of oxygen required to burn 20 grams of fat (9 kcal/gram).

  • Total kcal to burn 20 grams of fat = $(20 ext{ g} imes 9 ext{ kcal/g}) = 180 ext{ kcals}$.

  • For RQ = 0.80, $(3.20 ext{kcal/L O₂})$ is needed for fat.

  • Total liters of O₂ required = $(180 ext{ kcals} ext{ divided by } 3.20 ext{kcal/L O₂}) <br>ightarrow 56.3 ext{ liters}$.