[Sportsandrec] METs in short

[Thornbury, Kelly]

METs are metabolic equivalents , and are used to estimate how much oxygen (or through calculations how much energy) the body is using. Through calculations it can also be used to measure exercise intensity. One MET is equal to 3.5 milliliters of oxygen consumed for every one kilogram of body mass per minute (3.5 mL / kg / min). The value 3.5 is based on a 170 pound male of average physical fitness, and this number can actually be as low as 2.7 mL for small females (who have less muscle mass typically). One MET is also the approximate amount of oxygen (or energy) the body uses at complete rest, and an exercise intensity (which is what the elliptical is showing) of 7.5 METs equates to being 7.5 times more intense than rest. So as an example, if a person who weighs 80 kg (176 pounds) exercises at 7.5 METs for 30 minutes, then they burn: 
(3.5 * 7.5)mL * 80kg * 30min or
63 liters (63,000mL) of oxygen. 
One liter of oxygen is needed to burn approximately 4.8 to 5 calories (depending on what type of calories, carbs, fats, or proteins). For ease, the ACSM recommends using 5 calories for the equation, so the exerciser above burned approximately 315 calories during the  30 minute activity. 

METs can be calculated from exercises through different calculations like wattage on leg ergometers, speed and incline of treadmills (or track or cross country walking or running), or stepping exercises, and others. Be cautious of the readings from your exercise equipment however. We inquired to the manufacturers of our elliptical trainers in the gyms on campus as to how they calculated energy expenditure, and after being very closed-lipped about the information, we decided a couple of years ago to test the numbers on our own using a Metabolic Cart (a test instrument used to measure oxygen usage, or VO2, by collecting and analyzing exhaled gasses). Basically our ellipticals on campus over-estimated the exercisers burned calories by 20% over what we got from test data. Not all manufacturers use the same criteria for calculating calories, but just something to be aware of...The machine can't be 100% accurate without actually measuring exhaled air from the lungs. The more information the equipment requires (body weight, pulse, gender) the more accurate it can be. It also depends on the nature of the exercise (in cycling for example, you don't need to support your body weight with muscle, so the readings are different than treadmills where you are standing). 

Anyway, METs gets more involved and complicated, and the measurements you can calculate from METs is extensive...a whole semester's class worth, but that's it put short and sweet. 

Kelly