Q: I’m confused by the use of MET · minutes to describe weekly aerobic exercise. What does MET · minutes mean? What is its value? How can I use it with my clients?
A: MET minutes per week (MET · minutes · week−1) has become a common designation to summarize the amount and intensity of cardiorespiratory exercise. The 2008 Physical Activity Guidelines for Americans suggests substantial health benefits for adults engaging in 500 to 1,000 MET · minutes · week−1 of physical activity (6). The ACSM Position Stand on Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance of Prescribing Exercise also supports including 500 to 1,000 MET · minutes · week−1 of cardiorespiratory exercise (3).
MET stands for metabolic equivalent and reflects the energy expended by the body at seated rest. MET values for activities are the ratio of the rate of energy expended during an activity to the rate of energy expended at rest. For example, walking briskly on a level surface at 4.0 mph is equal to 5 METs (1). This means walking at that pace requires five times the energy compared with the energy cost when sitting at rest for an equivalent period. METs are therefore an easy way to describe the intensity of an array of physical activities (see the Table for some examples); the focus here will be on cardiorespiratory activities.
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TABLE: MET values for various cardiorespiratory activities (
1)*
MET · minutes is simply the time engaged in an activity with consideration to the number of METs. Consider the example of brisk walking at 4 mph. If a client walked at this pace for 30 minutes, the total would be 150 MET · minutes. This is calculated as follows:
If that client engaged in this activity 5 days per week, the total is 750 MET · minutes · week−1, calculated as follows:
With 750 MET · minutes · week−1 of walking, the client in this example meets the recommended amount of cardiorespiratory physical activity (recall that the target is 500 to 1,000 MET · minutes · week−1). Having a nice way to summarize the week’s activities can be especially helpful for individuals who select different modes and exercise intensities throughout the week. Using MET · minutes · week−1, one simple common value can be used to track progress (see the comparison in the box).
Classification of various activities is possible by using METs. The advisory committee for the 2008 Physical Activity Guidelines for Americans designated the following aerobic intensity categories based on MET levels (6) (note that these designations are reflected in ACSM guidelines as well (2,4)):
- Light-intensity aerobic activity = 1.1 to 2.9 METs
- Moderate-intensity aerobic activity = 3.0 to 5.9 METs
- Vigorous-intensity aerobic activity = 6.0 or more METs
Although the application of absolute aerobic intensity levels is useful with most healthy adults, intensity may best be defined relative to fitness for older adults (5,6). Because maximal aerobic capacity decreases with age, activities in the 3-to-6 MET range noted previously as “moderate intensity” may in reality be vigorous or beyond the capability of an older adult with a low fitness level (5). Thus, the following designations are recommended for older adults, or those with clinically significant chronic conditions or functional limitations, using relative intensity rather than absolute values:
- Moderate-intensity aerobic activity: effort level of 5 or 6 on a scale of 0 to 10 (note: 0 effort is sitting at rest and 10 is maximal effort)
- Vigorous-intensity aerobic activity: effort level of 7 or 8 on a scale of 0 to 10
Using relative intensity, along with supervision by a qualified fitness professional, can help older adults to optimize exercise intensity (5).
In addition to using MET · minutes · week−1, another option is to use METs to estimate the calories required for an activity. This can provide a weekly overview; the calculation takes into account the frequency, intensity, type, and time devoted to the activity. The energy costs determined by using METs in this manner will be approximations rather than precise values. MET values estimate energy costs and do not take into account individual differences in body mass, level of fat tissue, age, sex, movement efficiency, or environmental or geographic conditions.
For most adults, the minimum quantity of physical activity and exercise to promote health and fitness benefits equates to 1,000 kcal per week (kcal · week−1), although higher amounts of activity (energy expenditure of more than 2,000 kcal · week−1) result in greater benefits and may be needed to lose weight or to sustain weight loss (2). Realize that for clients with certain health conditions or with poor fitness, activity levels resulting in an energy expenditure below 1,000 kcal · week−1 may improve health and fitness (2).
Calculation of calories expended for a given exercise simply requires knowledge of the MET level, along with the person’s body weight in kilograms. These values can be entered into the following formula (note the bolded numbers 3.5 and 200 are both constants and do not change):
For a 150-lb (68.2-kg) woman engaging in the previous aerobic program that included brisk walking for 150 minutes per week (5 days per week, 30 minutes per day) at a 4-mph pace (5 METs), the total would be 900 kcal · week−1.
Realize that the determination of kcal · week−1 is an approximation and actual energy cost can vary depending on the efficiency of movement, body composition, and other factors not considered within the development of the MET values used in the formula.
CONCLUSIONS
Getting a handle on the volume of cardiorespiratory exercise can be challenging, especially when including a variety of activities of different intensities and durations. For the purposes of tracking or summing various aerobic activities, both MET · minutes · week−1 and kcal · week−1 can be useful. Educating your clients about the recommended targets for apparently healthy adults (at least 500 to 1,000 MET · minutes · week−1 or 1,000 kcal · week−1) may provide encouragement, regardless if their focus is to begin, continue, or increase their current programs.
References
1. Ainsworth BE, Haskell WL, Herrmann SD,
et al. The compendium of physical activities tracking guide. Healthy Lifestyles Research Center, College of Nursing & Health Innovation, Arizona State University; [cited 2011 Aug 22]. Available from:
https://sites.google.com/site/compendiumofphysicalactivities/.
2. American College of Sports Medicine.
ACSM’s Guidelines for Exercise Testing and Prescription. 8th ed. Philadelphia (PA): Lippincott Williams & Wilkins; 2010, 380 p.
3. Garber CE, Blissmer B, Deschenes MR,
et al. American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromuscular fitness in apparently healthy adults: guidance for prescribing exercise.
Med Sci Sports Exerc. 2011;43(7):1334–59.
4. Haskell WL, Lee IM, Pate RR,
et al. Physical activity and public health: updated recommendation from the American College of Sports Medicine and the American Heart Association.
Med Sci Sports Exerc. 2007;39(8):1423–34.
5. Nelson ME, Rejeski WJ, Blair SN,
et al. Physical activity and public health in older adults: recommendation from the American College of Sports Medicine and the American Heart Association.
Med Sci Sports Exerc. 2007;39(8):1435–45.
6. U.S. Department of Health and Human Services Web site [Internet].
2008 Physical Activity Guidelines for Americans. Atlanta, GA: U.S. Department of Health and Human Services; [cited 2011 Aug 22]. Available from:
http://www.health.gov/paguidelines.
