MET (Metabolic Equivalent of Task) gives the energy spent in a physical activity, per unit weight of the person.
1 MET is 1 calorie (1 kilocalorie, in scientific terms) energy consumption per kg of body weight per hour. Sitting idle is a 1 MET activity, and sleeping is a 0.9 MET one.
Research shows that there is something magical about activities involving 10 MET or above. If you can do any 10 MET–plus activity for more than 90 seconds, you are fit.
Translating this into a simple test: if you can run up 3 floors in 35 seconds, or 4 floors in 50 seconds, you have a good fitness level. Else, you have a poor fitness level.
Your chances of death in the next 5 years are 2-3 times more, if you have poor fitness than if you have good fitness.
The mortality risk due to fitness is modifiable. Do at least 150 minutes a week of moderate aerobic physical activity, or 75 minutes a week of vigorous aerobic physical activity or a combination of the two.
Read the full article for a list of METs of hundreds of activities. Also, read about different research papers showing how much each MET of improved fitness reduces your chances of death.
One is always interested in a simple, inexpensive test that can predict long–term health problems. If such a test exists, a healthy person can use it to know how healthy he really is.
There are several risk-scoring systems based on exercise, which measure short–term risk of dying. However, they are valid only in patients with heart disease. There were no tests that predict long–term risk of dying.
A simple new test uses the concept of MET to predict mortality risk (chance of dying).
MET (metabolic equivalent of task)
MET (metabolic equivalent of task) is roughly the energy expenditure in any physical activity, per unit weight of the person. One MET is roughly equal to 1 calorie (kilocalorie, in scientific terms) of energy consumption per kg of body weight per hour.
A person sitting idle will be burning 1 MET. It is easier to measure energy consumption by the amount of oxygen used. So, by convention, 1 MET involves using 3.5 ml of oxygen per kilogram per minute. It also turns out to be 1.1163 watts/kg of power output.
Difference between MET and BMR
The act of sleeping will consume 0.9 MET, so MET is different from BMR (Basal Metabolic Rate). BMR is the minimum energy consumption required by the body for survival. When you sleep, energy consumption is the bare minimum, as the body uses energy only for absolute necessities, such as respiration and blood circulation. In reality, your BMR is slightly lower than your energy consumption when you are sleeping.
However, when you are sitting idle, you are using some energy for watching (your eyelids are moving!), thinking, etc. So, you need nearly 11% more energy while ‘doing nothing’ than when you are sleeping.
In other words, your BMR is lower than 1 MET.
MET is a rough number
MET numbers are designed to account for body weight differences. After all, a heavier person would need more energy expenditure for the same task.
However, MET is still not an exact number. It varies a bit for different ages, genders, and body weights. For example, a person who is double in weight may have 2.4 times the energy consumption of the former person in some activities. So, you have to take the MET numbers as rough estimates and not rigid numbers.
MET for different activities
Here is a Compendium of Physical Activities that gives MET values for hundreds of daily activities. Table 1 below gives MET levels of various activities.
|Sitting, at desk / reading||1.3|
|Writing, desk work, typing||1.5|
|Standing, working on computer / talking on phone||1.8|
|Walking, 1.7 mph (2.7 kmph), level ground, strolling, very slow||2.3|
|Home activity – laundry–folding, putting away clothes||2.3|
|Walking, 2.5 mph (4 kmph)||2.9|
|Bicycling, stationary, 50 watts, very light effort||3.0|
|Walking, 3.0 mph (4.8 kmph)||3.3|
|Calisthenics, home exercise, light or moderate effort, general||3.5|
|Resistance (weight) training, multiple exercises, 8-15 reps||3.5|
|Home activity, cleaning, sweeping, moderate effort||3.5|
|Playing with children, moderate effort||3.5|
|Walking, 3.4 mph (5.5 kmph)||3.6|
|Gardening, general, moderate effort||3.8|
|Bicycling, < 10 mph (16 kmph), leisure||4.0|
|Resistance (weight) training, squats, explosive effort||5.0|
|Yardwork, mowing lawn, moderate-to-vigorous effort||5.0|
|Bicycling, stationary, 100 watts, light effort||5.5|
|Swimming laps, freestyle / crawl, light – moderate effort||5.8|
|Stationary cycling, moderate-to-vigorous effort (90-100 watts)||6.8|
|Hiking (hills with 5–10 kg load)||7.3|
|Calisthenics (e.g. pushups, situps, pullups, jumping jacks), heavy, vigorous effort||8.0|
|Bicycling, 12-13 mph (19–21 kmph), leisure, moderate effort||8.0|
|Circuit training, including kettlebells, vigorous intensity, minimal rest||8.0|
|Jogging, 5.6 mph (9.0 kmph)||8.8|
|Running, 6 mph (9.5 kmph)||9.8|
|Rope jumping (70/min)||10.0|
|Rope jumping (84/min)||10.5|
|Rope jumping (100/min)||11.0|
|Running, 6.8 mph (11.0 kmph)||11.2|
|Bicycling, mountain-biking, uphill, vigorous effort||14.0|
|Running, 14 mph (22.5 kmph)||23.0|
Light activities require less than 3 METs. Moderate activities consume between 3 and 6 METs. Vigorous activities consume more than 6 METs.
A 2002 paper in the New England Journal of Medicine used stress tests to evaluate people’s fitness. It found that people whose fitness was below 5 MET had twice as much chance of death as those whose fitness was above 8 MET over the following 6 years.
In both healthy people and those with cardiovascular disease, the peak exercise capacity achieved (highest MET levels they could sustain) was a stronger predictor of an increased risk of death than risk factors such as high blood pressure, smoking, and diabetes, as well as other exercise–test variables, including ST–segment depression (bad change in ECG or EKG waveform, during an exercise stress test), the peak heart rate, or the development of arrhythmias during exercise.
The trial also confirmed the protective role of a higher exercise capacity even in the presence of other risk factors. In other words, even if someone is suffering from risk factors such as high blood pressure and smoking, if he undertakes exercise and improves his fitness level, his risk of dying reduces.
The test found a 12% reduction in 6–year mortality risk for every 1 unit of MET improvement.
A 2009 paper in the Journal of American College of Cardiology found that heart patients whose fitness levels crossed 10 METs (had high exercise capacity) had no heart ischemia and so had no need for an expensive nuclear stress test to check their heart condition.
The heart pumps blood into the body. When one performs any exercise or activity, the muscles involved need more oxygen. This increases the demand on the heart and it has to pump harder and more often. So, the heart muscles need to work more. They, in turn, need more oxygen.
The blood vessels that supply blood to the heart muscles are called heart arteries. If they have any blockage, the blood flow through them is reduced. This is called ischemia, and is a dangerous condition.
If the oxygen demand for a particular heart muscle is not met, the cells in the muscle start dying. In turn, the heart muscle starts working less and less. The heart finds it difficult to pump more blood into the body, potentially leading to death.
In heart patients, long–term risk of heart ischemia is quite high, often leading to mortality. The study found that heart patients with 10 METs had pretty much no risk of heart ischemia. You can say that they were as good as normal people.
A 2011 paper in the Journal of Nuclear Cardiology found that heart patients who crossed 10 MET level of fitness had very low nonfatal heart attacks and risk of death due to heart–related problems, regardless of the peak heart rate achieved. In other words, they did not need to undergo any expensive testing to check their heart health: If they crossed 10 METs in their stress test, their heart was in good condition.
A 2016 article in the European Journal of Preventive Cardiology talked about inactivity as a leading predictor of early death, ahead of high BP and high cholesterol, second only to smoking. The study involved a massive 45 years of follow-up. So, its conclusions carry more weight.
- The scientists grouped 54-year-old men into 3 levels of fitness: low, medium, and high.
- Each increase in fitness category, from low to medium, and from medium to high, meant 21% less risk of death, over the next 45 years.
- Surprisingly, fitness in the early 50s mattered more than four decades down the line.
- In people with low fitness, even a small increase in activity levels had a beneficial effect.
Thus, the first three papers showed that high METs have a very good correlation with the health of heart patients. Above 10 METs, most heart patients are nearly as healthy as normal people. A new study used this 10 MET level of fitness to predict the risk of death.
A study presented at the Euro-Echo Imaging Conference 2018 used METs to develop a simple exercise test to predict the risk of death from Cardiovascular Disease (CVD), cancer, and other causes.
- 12,615 participants, between the ages of 18 to 91, with known or suspected coronary artery disease, were followed up for a median of 4.7 years.
- They underwent a treadmill test. The maximum MET reached by participants during the test was noted. The test can go from 5 METs to 20 METs.
- People who did not cross 10 MET were considered to have poor fitness. Those who crossed 10 MET were considered to have good functional capacity.
- After adjusting for age, gender, and other factors that could potentially influence the results, each extra MET achieved was independently associated with 9%, 9%, and 4% lower risks of cardiovascular death, cancer death, and other causes of death during the follow-up period.
- The death rate from heart disease was three times higher in the poor fitness group than the good fitness group (3.2% versus 1.2%, p<0.001).
- The death rate from cancer was two times higher in the poor fitness group than the good fitness group (1.5% versus 0.8%, p<0.001).
- The death rate from non-heart–disease, non-cancer causes was three times higher in the poor fitness group than in the good fitness group (1.7% versus 0.6%, p<0.001).
The researchers said:
The test for mortality risk
The scientists said that if anyone can run up 3 floors very fast (in 35 seconds), or 4 floors of stairs fast (in 50 seconds), he would have a fitness level of at least 10 MET.
So, instead of an expensive and cumbersome test, such as an exercise stress test, one can use the above test to predict the fitness level of a person, and the risk of death over the subsequent years.
The researchers claimed the test to be applicable to everyone, including normal people. But, since the fitness test was derived by testing participants with heart disease, I feel it should be applied only to heart patients.
One counter–argument to what I said is that a heart patient who can manage 10 MET activity is usually fit enough to be treated almost like a normal person. In that sense, the conclusions of the trial would be applicable to normal people, too, above 10 METs.
In other words, if a person can do more than 10 METs, his mortality risk is similar, whether he is a heart patient or not. This is the high-fitness group.
However, in the poor fitness group, which cannot do 10 MET activities, the mortality risk predicted by the study will be more than the actual risk in the normal group. The poor fitness group of heart patients should logically have a higher mortality risk than the poor fitness group of normal people.
The study also suggested that improving fitness would reduce the various risks of death. That is, the mortality risk due to fitness is modifiable.
European Society of Cardiology guidelines recommends at least 150 minutes a week of moderate aerobic physical activity or 75 minutes a week of vigorous aerobic physical activity or a combination of the two intensities.
This trial used the concept of maximum MET of a person to measure fitness, and therefore, the risk of dying. The peak MET was measured using a treadmill test.
For another fitness test to predict the risk of dying, read a detailed article on this website: A simple treadmill test to measure long–term risk of dying. This article sticks to the treadmill test to judge fitness. It also covers various aspects of an exercise treadmill test. The discussion on the treadmill test itself might make it worth reading the article.
First published on: 11th December 2018
Image credit: Image by Freepik
Last Updated on: 13th July 2023