Fitness guidelines love to talk about moderate and vigorous activity, and buried beneath those fuzzy words is an actual unit: the MET, short for metabolic equivalent of task. One MET is the energy your body burns while sitting quietly at rest. An activity rated at 5 METs makes your body work about five times harder than resting. It is a wonderfully simple idea — measuring exercise not in absolute terms, but as a multiple of your own idle engine.
The unit’s charm is that it automatically scales to the person. A large person and a small person burn different absolute calories on the same walk, but for both of them the walk is roughly the same multiple of their resting burn.
Where the numbers come from
By convention, one MET corresponds to consuming about 3.5 milliliters of oxygen per kilogram of body weight per minute, which translates to roughly one kilocalorie per kilogram per hour. Researchers have measured hundreds of activities in laboratories and compiled the results into reference lists ranging from sleeping, at slightly below 1 MET, to elite-level running at over 20. These published values are averages — your personal number depends on fitness, technique, and terrain — but they are consistent enough to compare activities honestly.
A feel for the scale
Typical values run roughly like this: light housework sits around 2 to 3 METs, brisk walking around 3.5 to 4, doubles tennis or casual cycling around 5, hiking or heavy yard work around 6, jogging around 7 to 8, fast cycling or competitive sports 10 and up. Guidelines commonly define moderate activity as about 3 to 6 METs and vigorous as above 6. When health authorities recommend 150 minutes of moderate activity a week, they are really prescribing a weekly dose of MET-minutes — intensity multiplied by time.
Turning METs into calories
The rule of thumb: calories burned per hour is roughly METs times body weight in kilograms. A 70 kg person cycling at 6 METs burns about 420 kcal per hour; a 90 kg person doing the same ride burns about 540. This is essentially the arithmetic your gym treadmill performs when it asks for your weight, which is also why machine calorie counts without a weight entry are little better than guesses. The framework also explains a humbling truth — an hour of vigorous effort can be undone by a single generous dessert.
Next time a guideline or gym display mentions intensity, translate it to METs — multiples of your own resting burn — and you can compare any two activities, or convert effort into calories, with one line of mental math.
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