Exercise is important, but conversations about it hit a snag when they turn to how much exercise you need. Doctors recommend 150 minutes a week of moderate exercise or 75 minutes a week if the exercise is vigorous. Many people, however, are unsure whether their exercise qualifies as moderate or vigorous. MET scores, or metabolic equivalents, are one way to bring better understanding.
A MET score of 1 represents the amount of energy used when a person is at rest. Using this as a baseline, scientists have given common activities MET scores. While MET scores have their limitations, they are useful starting points for discussing exercise.
The Basics of MET Scores
Humans require oxygen at about 3.5 milliliters per kilogram per minute when they are inactive. Scientists use that information to define a MET score of 1. They then assign higher MET scores to other, more strenuous tasks that require more oxygen.
MET scores work well for comparing tasks. They are less accurate when they are used to estimate the number of calories actually burned by an individual during a task. A 40-year-old man who weighed 70 kilograms (about 154 pounds) was used in the original calculations. Obviously, most people don't fit that age and weight profile.
MET Scores for Common Activities
Activities can be light, moderate, or vigorous, according to their MET score. The same activity can have more than one score. Riding a bike in a leisurely manner, for example, has a MET score of 3.5, while competitive mountain biking rates a 16.
Activities with a MET score of 1-4 are in the low-intensity category. They would not improve the cardiovascular fitness of most people, though they could be a good starting point for some. Activities with a MET score of 5-8 are classified as moderate and would be appropriate for those who are older or sedentary. Activities with a MET score over 8 are high intensity and are best for improving fitness as long as they can be done safely.
Here are some other common workouts and their MET scores:
- Walking on a firm, level surface at a very brisk pace: 5.0
- Running at the rate of a 10-minute mile: 9.8
- Low-impact aerobics: 5.0
- Swimming laps: 5.8
Everyday tasks also use energy and have their own MET scores, including:
- Moving furniture: 5.8
- Raking leaves: 3.8
- Washing windows: 3.2
- Walking the dog: 3.5
The Limits of MET Scores
People use energy at different rates. Two people doing a particular activity are unlikely to consume the same amount of energy, even though the MET score for the activity would be the same. Many factors influence the rate at which you use energy. These include:
- Age
- Gender
- Body weight
- Body composition
- Resting metabolic rate
- Cardiorespiratory fitness level
- Genetic traits
Testing Fitness Using MET Scores
Another use for MET scores is to show an individual's level of cardiorespiratory fitness (CRF), or the ability of the heart and lungs to supply oxygen to muscles during physical exertion. The best way of measuring CRF is with a VO2 max test, which requires the person being tested to use a treadmill while wearing an oxygen mask.
Many medical facilities do not have the equipment for VO2 max testing. Instead of VO2 testing, some facilities use MET scores derived from a stress test using a treadmill or stationary bike. If a stress test is not feasible, your MET score can be calculated by your answers to a questionnaire such as the Duke Activity Status Index.
Those with MET scores below 5 may be risking health problems. Any score below 7 should trigger concern. A score of 10 is good. Some occupations, such as firefighting, are best performed by those with a MET score of 12 or higher.
If you are not happy with your MET score, your doctor can help you figure out how to improve your exercise habits. An increase of 1 in your MET score, such as moving from a 5 to a 6, can lower your risk of heart disease and death by 10% to 20%.
Prescriptions for Exercise
Some doctors use MET scores to prescribe exercise for their patients, recommending, for example, 1,000 MET minutes a week. One MET minute equals one minute spent at a MET score of 1 (inactivity). To reach 1,000 MET minutes, a person could combine brisk walking and low-impact aerobics, both with a MET score of 5, for 200 minutes a week (5 x 200 = 1,000). Generally, an improvement in health requires 500-1000 MET minutes a week. You may need more MET minutes to lose weight.
Instead of using MET scores and MET minutes, some doctors and patients turn to fitness trackers to measure activity levels. Modern fitness trackers are different from the pedometers of old. They combine several technologies, such as sensors, the Global Positioning System (GPS), and heart rate monitors. They can generate detailed data about your exercise habits, and it's easy for you to share that information with your doctor.
