The Metabolic Equivalent of Task, often referred to as MET, represents a standardized measure of the energy cost of physical activities. It provides a simple, universal way to quantify the intensity and energy expenditure of various tasks relative to the energy consumed at rest. The concept of METs serves as a practical tool for researchers, health professionals, and individuals to assess physical activity levels.
Understanding the Metabolic Equivalent (MET)
A single MET quantifies the energy expenditure of sitting quietly. This resting metabolic rate forms the baseline for all other activity measurements. One MET is conventionally defined as consuming approximately 3.5 milliliters of oxygen per kilogram of body weight per minute. This also roughly translates to an energy expenditure of 1 kilocalorie per kilogram of body weight per hour.
The MET concept operates as a ratio, comparing the energy used during a specific activity to the energy used at rest. For instance, an activity with a value of 2 METs requires twice the energy expenditure of sitting still, while a 4 MET activity demands four times that resting energy. This relative measurement allows for a standardized understanding of activity intensity.
Quantifying Activity: How METs are Used
METs provide a practical framework for assigning intensity values to a wide array of physical activities.
For example, sleeping is rated at about 0.9 METs. Light activities, such as walking at a leisurely pace (around 2.0 mph), typically register at 2.5 METs, while brisk walking (3.0 mph) increases to approximately 3.5 METs. More vigorous activities, like bicycling under 10 mph, can be around 4.0 METs, and jogging generally falls around 7.0 METs. Even common household chores like moderate effort cleaning can reach 3.5 METs.
The utility of METs extends to allowing for a universal comparison of physical activity levels, independent of body weight, which simplifies the understanding of the relative intensity and energy cost across various tasks. To quantify the total volume of activity, MET-minutes are often calculated by multiplying the MET value of an activity by the number of minutes it was performed. For example, a 30-minute brisk walk at 3.5 METs would equate to 105 MET-minutes (3.5 METs x 30 minutes).
METs and Personal Health
Understanding METs directly links to achieving personal health outcomes and meeting physical activity guidelines. Accumulating a sufficient number of MET-minutes each week contributes significantly to reducing the risk of chronic diseases, including heart disease and type 2 diabetes. This accumulation also aids in managing body weight and enhancing overall fitness and well-being. Health organizations frequently utilize METs to categorize physical activities into different intensity levels.
Activities ranging from 3.0 to 5.9 METs are generally considered moderate intensity, exemplified by brisk walking or gardening. Activities rated at 6.0 METs or greater, such as running or vigorous swimming, fall into the vigorous intensity category. Current public health recommendations suggest adults aim for at least 150 minutes of moderate-intensity activity or 75 minutes of vigorous-intensity activity per week, which translates to roughly 500 to 750 MET-minutes per week. Meeting these targets offers substantial health benefits.
Factors Influencing MET Values
While MET values offer a standardized measure, the actual energy expenditure for a given activity can vary among individuals. Factors such as age, sex, body composition, and an individual’s fitness level influence how much energy is truly expended. A highly fit person might expend less energy for an activity than someone less fit, even if the activity has the same MET value.
Environmental conditions also play a role; for example, exercising on uneven terrain or in extreme temperatures can increase the energy cost beyond the average MET value. It is important to remember that published MET values are averages derived from research studies. They serve as useful estimates and a common language for comparing activities, though individual physiological responses may differ.