Calorimetry

Perhaps the test and measurements that best define exercise physiology are the incremental exercise test to maximal exertion for the quantification of the maximal rate of oxygen consumption (VO2max) as well as the detection and quantification of the metabolic threshold that signifies the transitions from steady state to non-steady state exercise. All this is possible thanks to the pioneering work of German, British and American scientists at the end of the 19th century, and the initial 20 years of the 20th century. These scientists, thanks to applications of bioenergetics, deduced that the body's energy release principles and laws must be no different to that of a machine. From this, basic macronutrients (carbohydtrates, fats, proteins) were treated like fuel for a machine, and energy input was compared to energy output in the form of physical work. If 1 gram of glucose could be burned in a flame to release a total package of energy (heat, light and sound), then surely the same gram of glucose when completely combusted in the body must release the same total energy. Such work was complemented at the same time by major discoveries in the biochemistry of energy catabolism, and it was shown that indeed, glucose combustion in the body causes the identical combustion of substrates and release of products (glucose + 6O2 -----> 6 CO2 + 6 H2O) as when burned in a flame. For steady state exercise, the body's consumption of oxygen (VO2) mirrored the increase in total energy expenditure. In addition, as carbohydrate and fat give off different amounts of carbon dioxide (CO2), it was also possible to detect differences in carbohydrate and fat combustion from whole body VO2 and carbon dioxide production (VCO2). Such facts form the framework of expired gas analysis indirect calorimetry (EGAIC), and the Topics of this section provide all the background you need to understand this field of science, and how it has been essential for the development of the discipline and applications of exercise physiology.