Indirect calorimetry can be performed in the same calorimetry chambers used for direct For Losing Weight While Pregnancy, since these sealed chambers are an optimal environment in which to measure gas exchange. For practical considerations, however, the most common form of indirect calorimetry is an open-circuit spirometry system in which a computerized mobile cart, or metabolic cart, allows the individual to breathe ambient air. The cart has technology that measures the amount of air inhaled, analyzes the oxygen and carbon dioxide content in the air, and measures the amount of carbon dioxide expired from the individual.
The portability of this system and lack of requirement for a sealed chamber permit the measurement of energy expenditure in educational settings. Semiportable metabolic carts can be used to measure energy expenditure in exercise physiology labs. These semiportable metabolic carts require access to a laboratory with equipment that is fairly expensive, which limits the practicality of these systems. Given that the individual is physically connected to the cart via a tube, there are only limited activities that can be measured, such as running, cycling, and rowing on treadmills and ergometers. Many other sports and activities cannot be measured using this technology, limiting its application.
In order to assess energy expenditure in an athlete’s actual environment and not in a research For Losing Weight While Pregnancy, more portable metabolic systems have been developed. These portable carts can be used in sport-specific contexts. A trade-off is that their accuracy is not as high as the laboratory measurement systems, though they still provide an acceptable measurement of energy expenditure with good reliability (Vogler, Rice, and Gore 2010). While these portable metabolic carts cannot be used in all sport contexts, the technology is continually evolving, helping to broaden their applicability to athletes.
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Portable metabolic carts have application not only to athletes but also in clinical settings. Indirect calorimetry using metabolic measurement systems is one of the most accurate assessments of resting energy expenditure (REE). REE, or resting metabolic rate (RMR), provides an estimate of the calories an individual needs at rest and can be measured by indirect calorimetry. Individuals lay in the supine position and breathe into a face mask attached to the metabolic cart for a period of time, typically about 20 to 30 minutes, and up to several hours for increased accuracy. Individuals should not eat for several hours or exercise for at least 24 hours before having REE or RMR measured. Measurements are most accurate when conducted early in the morning and when the individual has been resting quietly for a designated amount of time (such as 20 minutes).
To obtain a more precise assessment of basal metabolic needs, basal energy expenditure (BEE) or basal metabolic rate (BMR) can be measured. This is the amount of energy expended at complete rest. Individuals spend the night in a research laboratory so that their measurement can be taken immediately upon waking and before rising. Because this protocol is not always feasible or accessible, RMR is more often measured in practical settings such as health clinics and sports medicine facilities. For both BMR or RMR assessments, the individual should have refrained from strenuous exercise within the past 24 hours and should not have eaten in the past several hours (or be at least 8 hours fasted in the case of BMR), and the assessment should be conducted in a temperature-controlled environment that is free from loud or distracting noises. These protocols prevent external factors from affecting an individual’s RMR or BMR.
Indirect calorimetry is often considered a gold standard method for assessing REE. There is good accuracy and reliability when the procedure is completed with calibrated equipment (Pinheiro Volp et al. 2011). Metabolic carts can also measure VO2 max, which can be a useful training tool for athletes. While there is greater portability in newer technology, the trade-off is that a greater margin of error is introduced (Vogler, Rice, and Gore 2010). Additionally, the technology can be quite expensive and requires the presence of a trained administrator.
Indirect calorimetry can measure RMR and energy expended during physical activity; yet, in order to understand how these measurements fit into the overall energy needs of an athlete, one must understand the basic principles of energy balance.
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