Metabolic equivalent (MET)

The metabolic equivalent of task (MET) is a unit that expresses the energy cost of a physical activity as a multiple of resting metabolic rate, with 1 MET defined as the oxygen consumption of a seated adult at rest — approximately 3.5 mL O₂ per kilogram of body weight per minute (Jette 1990). Activities are classified as light (<3 METs), moderate (3–5.9 METs), or vigorous (≥6 METs); walking at 4 km/h registers roughly 3 METs, cycling at race pace exceeds 12 METs. Multiplying MET intensity by duration yields MET-minutes (or MET-hours), a standardised currency used in epidemiological surveillance and exercise prescription to compare diverse activities on a common scale, as codified in the Ainsworth Compendium of Physical Activities (2011 update, covering over 800 coded activities). In a pooled analysis of 661,137 adults followed for a median 14.2 years, Arem et al. (JAMA Internal Medicine, 2015) found a clear inverse dose-response between leisure-time MET-hours per week and all-cause mortality: participants achieving 7.5–15 MET-h/wk — the guideline-recommended minimum — showed 31% lower mortality compared with inactive peers, with the curve plateauing at approximately 22.5–40 MET-h/wk (39% reduction) and no evidence of harm at 10× the minimum. Because 1 MET is a population mean anchored to a 70 kg adult, individual resting oxygen uptake can deviate by ±20–30%, making MET-based intensity thresholds an approximation rather than a physiologically precise measure for any single person.