Other methods to assess EE

There are many other methods to estimate a value for the energy metabolism of living beings. They are somehow related to metabolites themselves or to the balance of body mass, body energy, body water or other components of the body. 

Modern equipment to measure HR limit the impairment to the subject. There are electrocardiograph tape recorders or telemetry systems to store the results of measurements. Finger clips with optical sensors for the blood pulse and some kinds of cuffs (like used to monitor the blood pressure) may be used to sense the heart rate over long periods. The individual relation between heart rate and EE measurements can be calibrated in whole body calorimeters as well as with mask calorimeters, performing different levels of activity. This calibration can later be used to estimate EE of free living subjects and/or over relatively long periods (up to some days). 

There may be temporarily pha.ses of anaerobic reactions not being fully compensated by aerobic ones. These phases have to be quite short because of the very limited tolerance of the body to the reaction products of anaerobic metabolism (lactic acid). This type of reaction has to be compensated later to regain normal balanced conditions. Indirect calorimetry would, if at all, just see short changes in RQ and EE. Heart beat measurements would see it as a peak of energy metabolism. 

Another commonly used method to determine EE of free living subjects utilises doubly labelled water [4-8]. Although the term doubly labelled 

The biological half-lives of the oxygen and hydrogen isotopes in the body are about 3 to 8 days. So the probes have to be taken daily for 7 to 14 days, depending on the metabolic activity of the subject. The subjects are not affected at all. 

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