The metabolic equivalent of task (MET) is the objective measure of the ratio of the rate at which a person expends energy, relative to the mass of that person, while performing some specific physical activity compared to a reference, currently set by convention at an absolute 3.5 mL of oxygen per kg per minute, which is the energy expended when sitting quietly by a reference individual, chosen to be roughly representative of the general population, and thereby suited to epidemiological surveys.
Vigorous household chores can add up to as much energy expenditure as dedicated exercise, so it is necessary to include both, suitably pro rata, in an assessment of general fitness.
An earlier convention defined the MET as a multiple of the resting metabolic rate (RMR) for the individual concerned.
The original definition of metabolic equivalent of task is the oxygen used by a person in milliliters per minute per kilogram body mass divided by 3.5.
Other definitions which roughly produce the same numbers have been devised, such as: where Still another definition is based on the body surface area, BSA, and energy itself, where the BSA is expressed in m2: which is equal to the rate of energy produced per unit surface area of an average person seated at rest.
Originally, 1 MET was considered as the resting metabolic rate (RMR) obtained during quiet sitting.
[4][5] Although the RMR of any person may deviate from the reference value, MET can be thought of as an index of the intensity of activities: for example, an activity with a MET value of 2, such as walking at a slow pace (e.g., 3 km/h) would require twice the energy that an average person consumes at rest (e.g., sitting quietly).
This value was first experimentally derived from the resting oxygen consumption of a particular subject (a healthy 40-year-old, 70 kg man) and must therefore be treated as a convention.