A doctor at the Cardiologic Hospital of Haut-Lévêque in Bordeaux, France, performs indirect calorimetry on a patient to measure inhaled levels of oxygen and exhaled levels of carbon dioxide.
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Indirect calorimetry refers to the measurement of oxygen consumption and carbon dioxide production. Heat measurement subsequently can be calculated using formulae to determine energy expenditure.
Metabolism is the sum of all chemical reactions occurring in the human body that are required to support body function and survival. The quantity of heat released from these chemical reactions can be measured, and then energy expenditure can be calculated. Calorimetry is the measurement of metabolism from heat release from the human body.
The quantification of VO2 and VCO2 requires the measurement of four variables: inspired ventilation, expired ventilation, FEO2, and FECO2. Most exercise physiology laboratories, however, do not measure both inspired and expired ventilation because of the expense required to purchase two ventilation-measurement systems. Therefore, the majority of commercially manufactured metabolic systems function with the use of a single ventilation-measurement apparatus (typically employed to quantify expired ventilation), from which the second measurement of ventilation is mathematically derived. The Haldane Transformation ( Figure 1 ) is a sequence of mathematical steps used to solve for inspired ventilation when this value is not actually measured. This process ultimately permits exercise scientists and others to quantify oxygen consumption, carbon dioxide production, and energy expenditure across various conditions of exercise.
Indirect calorimetry can be used to quantify the energy expenditure of various physical activities and exercise modalities. Scientific research has established a relationship between physical activity and multiple health outcomes including cardiorespiratory fitness, obesity, dyslipidemia, Type 2 diabetes, colon cancer, relative risk of developing cardiovascular disease, and relative risk of mortality from all causes. Based on these relationships, it has been noted that the health benefits of an exercise program are associated with the total weekly energy expenditure. Largely, based on these findings, a number of organizations have recommended an initial target energy expenditure of 1,000 kilocalories per week (kcal/wk) for previously sedentary individuals.
Modified from Porcari, John P., Cedric X. Bryant, and Fabio Comana. Exercise. Physiology. 1st ed. Philadelphia: F.A. Davis Company, 2015.
Exercise professionals, or others who design exercise programs, are then encouraged to gradually progress individuals toward a goal energy expenditure of 3,000 kcal/wk. This upper target energy-expenditure goal is based on evidence from the Harvard Alumni Study showing a graded inverse dose-response relationship between relative risk of all-cause mortality and levels of weekly physical activity.
Conversely, the assumption of equality between RQ and RER is not appropriate under all conditions. For example, in the following scenarios, RER will not reflect RQ:
The capability to accurately estimate energy expenditure during exercise is a fundamental aspect of exercise physiology, with fitness professionals and others frequently relying upon metabolic equations to prescribe exercise intensity and to determine the energy expenditure of different exercise modalities. Previous studies utilizing various exercise modalities, including arm ergometry, cycle ergometry, elliptical crosstrainer exercise, recumbent stepper exercise, vertical stairstepping, treadmill running, and treadmill walking have published prediction equations to estimate the oxygen consumption during exercise. From data collected in the laboratory with indirect calorimetry, multiple regression analysis has been used to develop prediction equations based on the relationship between mechanical workloads and the corresponding metabolic cost. To develop more accurate and valid estimates of oxygen consumption, these equations have periodically been researched to evaluate their accuracy and usefulness. Metabolic equations for the prediction of energy expenditure during common exercises are presented in Table 2
American College of Sports Medicine. ACSM's Guidelines for Exercise Testing and Prescription. 9th ed. Philadelphia: Lippincott Williams & Wilkins, 2014.
Porcari, John P., Cedric X. Bryant, and Fabio Comana. Exercise Physiology. Philadelphia: Davis, 2015.
Blair, Steven N., et al. “Physical Fitness and All-Cause Mortality: A Prospective Study of Healthy Men and Women” JAMA 262, no. 17 (November 3, 1989): 2395–401.
Paffenbarger, Jr., R. S., et al. “Physical Activity, All-Cause Mortality, and Longevity of College Alumni” New England Journal of Medicine 314, no. 10 (March 6, 1989): 605–13.
Robergs, Robert. “Indirect Calorimetry” University of New Mexico. http://www.unm.edu/~rrobergs/426L11IndCalorim.pdf (accessed February 5, 2017).
American College of Sports Medicine (ACSM), 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 637-9200, Fax: (317) 634-7817, http://www.acsm.org .
American Council on Exercise, 4851 Paramount Dr., San Diego, CA, 92123, (858) 576-6500, (888) 825-3636, ext. 782, Fax: (858) 576-6564, https://www.acefitness.org .
Lance C. Dalleck, PhD