When is indirect calorimetry necessary?
It is possible to measure the heat generated by living organisms by direct calorimetry, in which the entire organism is placed inside the calorimeter for the measurement.
It is not always possible to do this with larger subjects.
In such cases, indirect calorimetry is used.
Indirect calorimetry uses oxygen consumption and carbon dioxide production during rest and steady-state exercise to estimate energy metabolism.
If all the oxygen is used to oxidize fuels and all the carbon dioxide produced is recovered, it is possible to calculate the total amount of energy produced.