Which is the best metric for measuring your activity level, intensity minutes, calories or MET-hrs? The WHO (World Health Organization) guidelines are 150-300 minutes moderate intensity activity or 75-150 minutes of vigorous intensity activity a week. While this is a good guideline for people who are starting out from a relatively inactive lifestyle, some people may want to monitor their activity level more accurately.
Activity that raises your heart rate to 50%-70% of your maximum heart rate is counted by Garmin as moderate intensity, and activity that raises your heart rate to above 70% is counted as vigorous intensity. Garmin's intensity minutes feature is calculated as 1x moderate intensity minutes + 2x vigorous intensity minutes. Also, only activity of at least 10 minutes in duration are counted. From the above it is evident that quite a wide range of activity level can result in the same intensity minutes score.
Therefore calories expended (or more properly, active calories, which are total calories minus calories expended at rest) might be a more granular and accurate measurement of activity level. However, the number of active calories you need to expend to meet activity guidelines depends at least on your weight and possibly other factors. This is where METs (Metabolic Equivalent) measurement can be beneficial. One MET is the rate of energy expenditure at rest, 2 METs is twice the rate of energy expenditure at rest, etc. 1 MET is defined as 1 kcal/kg/hr, and MET-hrs (METs x hours) is the measure of energy expended. The benefit of MET-hrs is that is can be used to compare (or prescribe) the same amount of phyical activity for people regardless of weight.
See my FitRate, MET Datafield, MM Chrono, Geo Chrono, Top Gun Chrono, MET datafield, Aerospace+H, Night Mission, Night Mission SE, Navigator+H, Navigator 24h, Ironman Red and Endurance apps for their METs and MET-hr display features.
FitRate determines your activity level in the past week (measured in MET-hrs/week) and gives you a relative ranking (poor, fair, good, excellent, etc) and also estimates the years of life you will gain (after the age of 40) if you maintain this activity level.