Metabolic Equivalent of Tasks

Metabolic equivalent of tasks (METS), which is sometimes shortened to metabolic equivalents, is a standard measure in physiology used to denote the physical intensity involved while exercising at different intensities for various physical activities. METS are calculated as the ratio of the work metabolic rate (rate of energy consumption during a specific physical activity) to the resting metabolic rate (rate of energy consumption while sleeping). This plural form is sometimes stated in its singular form: metabolic equivalent of task (MET).

METS are measures of the amount of oxygen used by the body during various types of activities or exercises. The term MET is used to express an individual's metabolic rate while performing some type of task based on that person's resting metabolic rate. The resting MET is measured as 1. That is, 1 MET is the amount of energy, as determined from the amount of oxygen inhaled, used by the body at rest. Activities considered to be resting include sitting quietly on a chair or reading a book while lying on a bed.

When more strenuous (nonresting) activities are pursued, such as walking at about 3 mi. (4.8 km) per hour, bicycling on flat terrain, and mowing the grass with a push mower, the body expends more energy and, thus, the body inhales more oxygen. Then, when such activities occur, MET values are higher. The METS for various nonresting tasks range from 1.5 to 18.0.

Anyone can use METS to determine the intensity of a workout or for everyday activities around the house. When METS are used, calories per hour can be determined for a weight-loss program or to gauge intensity levels for a particular fitness level desired.

The various values for METS were first standardized within the Survey of Activity, Fitness, and Exercise (SAFE Study—1987 to 1989). Called the Compendium of Physical Activities, they were developed by Dr. William Haskell, from Stanford University (California). In 2017, Dr. Haskell was a professor (research) of medicine, emeritus, at the Stanford Prevention Research Center.

Originally, Haskell created a five-digit code that identified the category (heading) of physical activity (the first two digits) and the type of activity (the last three digits). For example, “01010” referred to “01” for “bicycling” and “010” stood for “bicycling at less than 10 miles per hour, for leisure, to work, or for pleasure.” The first version of the Compendium was published in 1993 and the last update to it was published in 2011 (as of December 2016).

The MET is a unit of standard metabolic equivalent used to estimate an individual's metabolic rate while performing some task based on that person's resting metabolic rate (RMR). Two well known measures of RMR, which is also denoted as 1 MET, are the consumption of (1) 1 kilocalorie (kcal) per kilogram (kg) of body weight per hour (h) and (2) 3.5 milliliters (ml) of oxygen (O2) per kilogram (kg) of body weight per minute (min). MET values range from 0.9 MET when sleeping to 18.0 MET when running at 10.9 mi. (17.5 km) per hour.

One MET is also defined as 58.2 watts per meter squared (W/m²) or equivalently as 18.4 British thermal units per hour times feet squared (BTU/h × ft²). These terms equal the rate of energy produced per unit surface area (either in square meters or square feet) of an average adult at rest in the sitting position.

The value of 1 MET is the base metabolic equivalent of task, or the metabolic rate of a person who is at rest. The amount of energy expended for any activity is measured in METS, which are multiples of a person's base metabolic rate (1 MET).

A value of 3 MET to 6 MET is considered to be moderate physical activities. Moderate (low-intensity) physical activity is generally determined to be any activity that causes the heart rate or breathing to increase. Such activities usually burn 3.5 to 7.0 calories (cal) per minute (kcal/min).

Any MET values from 7 to 18 are considered vigorous physical activities. Examples of vigorous (high-intensity) activities are playing a strenuous game of tennis, doing demanding calisthenics, snow skiing down a hill, water skiing on a lake, and swimming competitive laps in a pool. When such levels are attained, breathing and heart rates are rapid, and the body is forced to expend quite a bit of energy to perform such activities. Vigorous physical activities expend 8.0 or more calories per minute; this value may vary, however, depending on fitness level, weight, age, and other such factors.

For instance, a man who is horseback riding has a MET of about 3.5, meaning that his metabolic rate is 3.5 times than his resting metabolic rate. A woman who is backpacking has a 7 MET, or a metabolic rate that is seven times higher than her resting rate. METS for other activities include:

According to the Physical Activity Guidelines for Americans (2008, the latest edition as of 2017), which is produced by the U.S. Office of Disease Prevention and Health Promotion, adults should engage in from 500 to 1,000 MET minutes per week.

An Exercise Metabolic Test is one way to determine factors relating to MET. During the test, a person will exercise on a treadmill or a bicycle that is attached to an ergometer (a device for measuring work performed). The participant is hooked to a breathing device and gas analyzer. The operator of the equipment has the participant increase their level of exercise intensity, which causes the consumption of oxygen to increase. When the oxygen level does not rise further, but the exercise intensity level continues to increase, then the gas analyzer will determine the VO₂max, or the maximum (max) volume (V) of oxygen (O₂).

The test shows how an individual responds to physical activity at different levels of intensity. The equipment also produces some of the following statistics: calories burned per minute while exercising; percent of calories from fat, carbohydrates, and protein; volume of carbon dioxide (CO₂) exhaled (VCO₂); and heart rate. The test is used for people who have breathing concerns such as shortness of breath, desire to lose (or gain) weight, or want to know their peak performance level.

There are no known medical risks for using metabolic equivalent of tasks. However, MET values are based on a large sample of people representing an even much larger population. Therefore, these values are average values and may vary depending on differences among individuals, such as fitness level, age, speed, intensity, conditions while exercising, and other such factors.

By knowing one's MET value for a particular exercise, it is possible to estimate the number of calories that will be burned while participating in physical activities. Many websites provide tools to calculate the number of calories burned while exercising. One of them, which provides a step–by–step procedure for this measurement, is “How to Calculate Calories Burned” from Ethika Clinic in Kolkata, India. It is found at: https://ethikaclinic.wordpress.com/a-healthy-life/calculatecalories-burnt/ .

William A. Atkins, BB, BS, MBA