What is a Metabolic Equivalent?

Metabolic equivalent of task, known as MET or metabolic equivalent, is a concept frequently used to indicate the amount of oxygen or energy the body uses during physical activity. A unit of metabolic equivalent expresses the ratio of an average person's metabolic rate while performing some task compared to their metabolic rate at rest. In practical application, MET is a way of comparing the level of exertion and the energy spent when people of different weights perform the same physical activity. Metabolic equivalent can also compare the aerobic intensity and energy expenditures of various physical activities when performed by one person.

It is conventionally agreed that 1 MET is the equivalent of the energy or oxygen the body uses while at rest. One MET is considered the resting metabolic rate, or the metabolic rate at which the body consumes 3.5 milliliters of oxygen per kilogram of body weight per minute. In mathematical terms, 1 MET = 50 kcal/hour/m2 body surface area.

The harder a body works during any given activity, the more oxygen is consumed, and the higher the correspondingly MET level. Activity between 3 and 6 METs is considered moderate-intensity, such as walking the dog. A person experiences an increase in breathing and heart rate and 3.5 to 7 calories are burned per minute. Vigorous activity, 6 METs or higher, burns more than 7 calories per minute and includes running and playing basketball.

The MET concept can be used to make fitness recommendations, to plan or monitor physical activity, or to measure levels of aerobic intensity. For example, it is recommended that people get for 500 to 1,000 MET-minutes per week for good health. This is the equivalent of at least 150 minutes of moderate-intensity or 90 minutes of vigorous intensity activity per week. The concept of metabolic equivalent is also useful for prescribing exercise, such as determining the activity required for rehabilitation of patients with various conditions.

METs are estimated predictions based on controlled experiments and are highly inaccurate when applied to specific individuals. Actual energy expenditure, often described as "calories burned," during a physical activity depends on a person's body mass, fitness level, and a variety of other circumstances. Published metabolic equivalent values and exercise "calorie calculators" based on METs are only averages and should not be used by individuals. Measuring actual METs usually involves a treadmill test, where a person wears a mask that measures oxygen consumption and carbon dioxide exhalation.