Chapter 8

Copyright © 2007 Lippincott Williams & Wilkins. McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

Chapter 8

Measurement of Human Energy Expenditure


Methods of Measuring Body’sHeat Production

Two methods

• Direct calorimetry

• Indirect calorimetry


Direct Calorimetry

• Airflow calorimeter– Temperature change in air that flows through

an insulated space × air’s mass and specific heat

• Water flow calorimeter– Change in temperature flowing through coils

embedded in an environmentally self-contained suit


Direct Calorimetry

• Gradient layer calorimetry– Measures heat flowing from the subject through

a sheet of insulating materials with piping and cooler water on outside

• Storage calorimetry– Subject sits in a known mass of water at a

constant temperature. Changes in water temperature are measured.


Indirect Calorimetry

• Closed-circuit spirometry– Subject breathes into a spirometer.– Soda lime is used to absorb carbon dioxide.




• Open-circuit spirometry– Portable spirometry

• Spirometer is small and is carried in a pack.

• Air volume is metered.

• Sample is collected to measure concentrations of gases.




• Bag technique– Air is collected in a large bag (Douglas Bag).– Small sample is measured for gas

concentrations.




• Computerized instrumentation– Air flow is measured for volume.– Gas analyzers measure concentrations of oxygen

and carbon dioxide.


Doubly Labeled Water Technique• Isotope-based method

• Doubly labeled water contains– Oxygen-18 or 18O– Deuterium or 2H

• Isotopes consumed in a known volume of water

• Isotopes distribute throughout body fluids

• Hydrogen leaves body as 2H2O in sweat and urine

• Oxygen leaves body as C18O2 or H218O

• Estimates total daily energy expenditure


The Respiratory Quotient (RQ)• RQ = CO2 produced / O2 consumed

– RQ for carbohydrate = 1.00– RQ for fat = 0.696– RQ for protein = 0.818– Nonprotein RQ = 0.86– RQ for a mixed diet = 0.82

• RQ – assume that oxygen consumption and carbon dioxide production measured at mouth reflect activity in tissues


Respiratory Exchange Ratio (RER)

• Ratio of CO2 produced to O2 consumed

• Calculation of RER is the same as RQ

• Metabolic calculations– Calculating energy expenditure during exercise– Volume of air

– Concentrations of O2 and CO2

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Chapter 8