metabolic equivalent of task

The Compendium of Physical Activities, the reference list these values come from, defines METs as the ratio of an activity's energy cost in millilitres of oxygen per kilogram per minute against a standardised resting metabolic rate of 3.5 mL/kg/min, or roughly 1 kilocalorie per kilogram per hour. That standard was fixed by Balke in 1960 and has been kept since so that values can be compared between studies. The Compendium classifies sedentary behaviour at 1.0 to 1.5 METs, light intensity activity at 1.6 to 2.9, moderate intensity at 3.0 to 5.9, and vigorous intensity at 6.0 and above.

MET-minutes are what turn an intensity into a dose. Herrmann and colleagues, in the 2024 update of the Compendium, explain that MET-minutes and MET-hours are computed by multiplying an activity's MET value by the minutes or hours spent doing it, and they work an example: an electrically assisted bike ride rated at 6.0 METs for 30 minutes comes to 180 MET-minutes. For scale, they note that the 2018 United States physical activity guidelines, 150 to 300 minutes a week of moderate intensity activity, amount to roughly 500 to 1,000 MET-min a week.

What a MET does not describe is an individual. The Compendium's authors are explicit that it can serve as a starting point for prescribing individual activities but does not reflect precise individual energy expenditure, because resting metabolic rate itself varies with age, sex, height and body weight. They cite a study reporting energy expenditure 8 to 15 percent higher in women with obesity than in women without, across several treadmill speeds and grades. A MET also counts oxygen used and nothing else, so it says how hard the body is working metabolically rather than what an activity does mechanically.