Oxygen consumption per kg of body weight or metabolic equivalent (MET).

This dimension is attributed to the triiodothyronine activity. We can arrange organs, in descending order, in respect of triiodothyronine influence on the oxygen consumption per kilogram body weight as follows: heart (10-11%), gastric mucosa, liver, smooth muscles: 4-5%, kidneys (1%), diaphragm (4%). 

In epidemiological studies, estimation of total energy expenditure can only be carried out from using metabolic equivalent (MET) units calculated physical activity questionnaires, where 1 MET is generally assumed to be 3.5 ml/min/kg resting oxygen consumption (VO2 resting). Since the basal metabolic rate varies with age, the energy expenditure equivalent to 1 MET is likely to vary with age.

One metabolic equivalent (MET) is defined as the amount of oxygen consumed while sitting at rest and is equal to 3.5 ml O2 per kg body weight x min. The MET concept represents a simple, practical, and easily understood procedure for expressing the energy cost of physical activities as a multiple of the resting metabolic rate. The energy cost of an activity can be determined by dividing the relative oxygen cost of the activity (ml O2/kg/min) x by 3.5.

Metabolic equivalents, or METs, are routinely employed as a guide to exercise training and activity prescription and to categorize cardiorespiratory fitness (CRF). There are, however, inherent limitations to the concept, as well as common misapplications. CRF and the patient's capacity for physical activity are often overestimated and underestimated, respectively. Moreover, frequently cited fitness thresholds associated with the highest and lowest mortality rates may be misleading, as these are influenced by several factors, including age and gender. The conventional assumption that 1 MET = 3.5 mL O2/kg/min has been challenged in numerous studies that indicate a significant overestimation of actual resting energy expenditure in some populations, including coronary patients, the morbidly obese, and individuals taking β-blockers. These data have implications for classifying relative energy expenditure at submaximal and peak exercise. Heart rate may be used to approximate activity METs, resulting in a promising new fitness metric termed the "personal activity intelligence" or PAI score. Despite some limitations, the MET concept provides a useful method to quantitate CRF and define a repertoire of physical activities that are likely to be safe and therapeutic. In conclusion, for previously inactive adults, moderate-to-vigorous physical activity, which corresponds to ≥3 METs, may increase MET capacity and decrease the risk of future cardiac events.

https://pubmed.ncbi.nlm.nih.gov/15223593/

https://pubmed.ncbi.nlm.nih.gov/29229271/