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Definitions and the First Law of Thermodynamics
Published in Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will, Commonly Asked Questions in Thermodynamics, 2022
Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will
Calorimetry is the science of measuring heat associated with physical, chemical or biological processes. These processes can either release (exothermic) or absorb heat (endothermic). We distinguish between direct calorimetry, which is explained in the following questions, and indirect calorimetry. In indirect calorimetry, the amount of heat is calculated indirectly from the measured oxygen consumption. For this purpose, a relationship between heat evolution and oxygen consumption, called the oxycaloric equivalent (–430 to –480 kJ mol−1), is exploited (Gnaiger and Kemp 1990). This is particular useful for large organisms such as humans! Direct calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning “heat” and the Greek word μέτρον (metron), meaning measure.
Business Improvement through Innovation in Construction Firms: The ‘Excellence’ Approach
Published in Ben Obinero Uwakweh, Issam A. Minkarah, 10th Symposium Construction Innovation and Global Competitiveness, 2002
Herbert S. Robinson, Patricia M. carrillo, Chimay J. Anumba, Ahmed M. Al-Ghassan
The idea behind indirect calorimetry is quite simple. Since oxygen is used and carbon dioxide is produced during energy-yielding reactions, exhaled air contains less oxygen and more carbon dioxide than inhaled air. The difference in composition between inspired and expired air volumes reflects the body’s release of energy through aerobic metabolic reactions. Research has shown that for every liter of oxygen consumed, 4.83 kilocalories of energy, on average, are produced. Thus, by measuring the rate of oxygen consumption before, during, and after performance of physical activities, the total energy expended by a human can be estimated. It should be noted that the conversion multiplier varies slightly depending on a physiological attribute termed the “Respiratory Quotient”. This method of estimating energy expenditure from oxygen uptake is referred to as “indirect calorimetry”. Compared to direct calorimetry, indirect calorimetry provides a reasonably accurate, portable, and relatively inexpensive method of measuring energy expenditure.
Modelling Heat Losses from the Human Body
Published in Ivana Špelić, Alka Mihelić-Bogdanić, Anica Hursa Šajatović, Standard Methods for Thermal Comfort Assessment of Clothing, 2019
Ivana Špelić, Alka Mihelić-Bogdanić, Anica Hursa Šajatović
In the 1980s, the first calorimeters were produced in order to continuously measure both evaporative heat loss and dry heat exchange from the human body. The respiratory and sweating component of evaporative heat loss was quantified by recirculating air through a system of freezers to absorb water (McLean and Tobin, 1987). Calorimetry is the term applied to the measurement of the exchange of heat. The direct calorimeter measures the heat exchange directly based on a person performing an activity in a controlled environment, while indirect calorimetry involves estimation of the energy exchanges from the measurement of material exchanges. Indirect calorimetry uses the rate of oxygen consumption to estimate metabolic rate. There are two main types of direct calorimeter: one depends on absorbing the body’s heat loss and measuring the rise in temperature in the absorbing medium. The other measures the temperature difference produced across a layer surrounding the body as the result of heat flow from the body to its surroundings (Ingram and Mount, 1975; Parsons, 2001). The direct calorimetry is not a practical option for thermal comfort assessment; however, the indirect calorimetry methods also have their flaws, and it is not possible to obtain an accurate estimate of metabolic heat production. The subjects are exposed due to the interference which the equipment has on the activity of the person. There is also a noticeable variation for the same activity between different subjects, variation for the same activity when comparing multiple experiments and problems with calibration and leaks in the equipment. The second issue is that with the high levels of activity the concept of thermal comfort may change due to profuse sweating, blood redistribution and hormonal secretions, which impacts productivity, physical and thermal strain (Parsons, 2001).
The effect of exercise interventions on resting metabolic rate: A systematic review and meta-analysis
Published in Journal of Sports Sciences, 2020
Kristen MacKenzie-Shalders, Jaimon T. Kelly, Daniel So, Vernon G. Coffey, Nuala M. Byrne
Human energy expenditure has three primary components: activity energy expenditure, resting metabolic rate (RMR) and dietary-induced thermogenesis (DIT) (Levine, 2005). The accurate measurement and interpretation of RMR is beneficial as it is a principal contributor to daily energy expenditure. In practice, this is usually measured by Indirect Calorimetry, a method that is “indirect” as it measures airflow and the percentage of oxygen (O2) and carbon dioxide (CO2) to generate the respiratory exchange ratio (RER) which is subsequently converted to energy expended through known relationships (Levesey, 1988; Lusk, 1924). It is important for practitioners to understand how behaviours and lifestyle can impact on components of energy expenditure, in particular, the effect of exercise on RMR is of interest as it has implications for health and sports performance. Despite this, there is a lack of agreement in the literature regarding the potential for exercise to modulate RMR in humans.
A short bout of high-intensity intermittent exercise before moderate-intensity prolonged exercise as a mean to potentiate fat oxidation ?
Published in Journal of Sports Sciences, 2020
Anna Borowik, Samarmar Chacaroun, Damien Tessier, Stéphane Doutreleau, Samuel Verges, Patrice Flore
First of all, an extension of the recovery period would have strengthened the main conclusion of our study. (Peake et al., 2014) Also, this study provides data obtained almost exclusively with indirect calorimetry. Additional plasmatic variables such as catecholamine, blood glucose, glycerol and non-esterified fatty acids would be required to support our results. Indirect calorimetry is the most commonly used technique for assessing the balance between fat and carbohydrate (CHO) oxidation during exercise. However, its validity is questionable for exercise intensities greater than 75% V̇O2max. (Jeukendrup & Wallis, 2005) One way to resolve the actual energy expenditure from fat after HIIE and its consequences on bicarbonate pool issues would have been to associate indirect and whole-body calorimetry in a metabolic chamber. Another would be to directly study fat oxidation by femoral arterial and venous catheterization, through muscle biopsies and tracer methodologies or with a breath 13 C/12 C ratio technique. (Nedeltcheva et al., 2010)