Metabolic equivalent

A unit of metabolic equivalent, or MET, is defined as the ratio of a person's working metabolic rate relative to the resting metabolic rate. One MET is defined as 1 kilocalorie per kilogram per hour and is the caloric consumption of a person while at complete rest. For example, one might consider the restful state following a quiet night's sleep as a good example of a single MET. This is a base-line unit for that one individual, and since each individual has a varying BMR, a MET is, therefore, variable from one person to the next. One might consider a single unit the energy required to just stay alive without doing anything more.

The unit is commonly used in the context of aerobic exercise to gauge the intensity of the workout. A workout of 2-4 METs is considered light, while intensive running (8 minutes/mile, or 12 km/h) or climbing can yield workouts of 12 or more METs.

Since METs are variable units, they can only be used in calculating relative energy expenditures in "context;" meaning within the parameters per individual, unlike caloric expenditures which are unitary standards not variable from one person to another. While exercising at 6 METs, a 200-pound (90 kg) man would burn considerably more calories than his 120-pound (55 kg) son doing the same exercise.

METs are particularly relevant to those who intend to lose weight, because they are a simple approximation of the rate at which exercise causes calories to be burned. Many modern exercise machines can indicate METs, although the numbers given are estimates since, as mentioned above, the rate at which calories are burned while at rest (the Basal Metabolic Rate or, more strictly, the Resting metabolic rate: RMR) varies from person to person.

Some exercise machines estimate METs based on the formula: cpm/kg.  This convenient non-individualized approximation is often used, including in scientific literature. "No work requires only “basal metabolism,” or about 3.5 mL O2/kg/minute, also known as 1 MET."  "One MET is defined as the energy it takes to sit quietly. For the average adult, this is about one calorie per every 2.2 pounds of body weight per hour someone who weighs 160 pounds would burn approximately 70 calories an hour while sitting or sleeping."