What is a Metabolic Equivalent of Task (MET)?

A MET (Metabolic Equivalent of Task) is a physiological measure that quantifies the energy cost of physical activities, with one MET representing the energy expended while sitting quietly (3.5 mL/kg/min oxygen uptake).

How are MET hours calculated?

MET hours are calculated by multiplying the MET value of an activity by the duration for which that activity was performed, expressed in hours (MET Hours = METs × Duration in hours).

Why are MET hours important in health and fitness?

MET hours are important for exercise prescription, establishing public health guidelines (e.g., WHO/CDC recommendations), conducting large-scale research on physical activity and health outcomes, and providing a standardized way to track total energy expenditure.

Where can I find reliable MET values for different activities?

Reliable MET values for various activities can be found in widely recognized resources such as the "Compendium of Physical Activities," which provides a comprehensive list.

What are the limitations of using MET hours?

Limitations of MET hours include individual variability in actual energy expenditure, the generalized nature of average MET values, challenges in accounting for fluctuating activity intensities, and that they do not reflect all training variables beyond energy expenditure.

What are MET hours?

MET hours represent a standardized measure of the total volume of physical activity performed, calculated by multiplying the Metabolic Equivalent of Task (MET) value of an activity by the duration in hours, providing a quantifiable metric for energy expenditure.

Understanding METs: The Foundation

Before delving into MET hours, it's crucial to grasp the concept of a Metabolic Equivalent of Task, or MET. A MET is a physiological measure expressing the energy cost of physical activities and is used to describe the intensity of an activity.

Definition: One MET is defined as the energy expended while sitting quietly. Specifically, it equates to an oxygen uptake of 3.5 milliliters per kilogram of body weight per minute (3.5 mL/kg/min). This serves as a baseline for energy expenditure.
Purpose: METs provide a simple, convenient, and standardized way to describe the absolute intensity of a wide range of physical activities, allowing for comparisons across different activities and individuals, regardless of body weight.
Activity Classification by METs:
- Light-intensity activities: Typically < 3.0 METs (e.g., slow walking, light housework).
- Moderate-intensity activities: Typically 3.0 to 5.9 METs (e.g., brisk walking, recreational swimming, cycling).
- Vigorous-intensity activities: Typically ≥ 6.0 METs (e.g., running, competitive sports, high-intensity interval training).

From METs to MET Hours: Quantifying Activity

While METs describe the intensity of an activity, MET hours extend this concept to quantify the total volume or total energy expenditure of that activity over a specific duration.

Calculation: MET hours are calculated by multiplying the MET value of an activity by the duration for which that activity was performed, expressed in hours.
- Formula: MET Hours = METs × Duration (in hours)
Purpose: This metric allows health professionals, researchers, and individuals to track and compare the cumulative energy expenditure from different types and durations of physical activity. For example, 3 MET-hours could be achieved by walking at a moderate pace (3 METs) for one hour, or by performing a vigorous activity (6 METs) for 30 minutes (0.5 hours). Both scenarios result in the same total MET hours, indicating a similar overall energy cost.

Practical Applications of MET Hours in Health and Fitness

MET hours are a fundamental metric used across various domains of exercise science and public health.

Exercise Prescription: Fitness professionals often use MET values and MET hours to design exercise programs that meet recommended physical activity guidelines. Understanding the MET equivalent of various exercises helps in prescribing appropriate intensities and volumes.
Public Health Guidelines: Major health organizations, such as the American College of Sports Medicine (ACSM), the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO), frequently reference METs and MET hours in their physical activity recommendations for health benefits. For instance, the recommendation of 150 minutes of moderate-intensity activity per week roughly translates to 500-1000 MET-minutes per week (or 8.3-16.7 MET-hours), which is often cited as the minimum target for significant health benefits.
Research and Epidemiology: In large-scale epidemiological studies, MET hours are widely used to assess physical activity levels in populations and to investigate the relationship between physical activity volume and various health outcomes, such as reduced risk of chronic diseases (e.g., cardiovascular disease, type 2 diabetes, certain cancers).
Personal Tracking: While less common for everyday fitness trackers, the underlying principles of METs and MET hours inform how many devices estimate calorie burn and activity levels. For the knowledgeable individual, understanding MET hours can provide a more nuanced perspective on their accumulated exercise volume beyond just steps or duration.

Calculating MET Hours: A Step-by-Step Guide

To calculate MET hours for your activities, follow these steps:

Determine the Activity's MET Value: Consult a reliable source for the MET value of your specific activity. The "Compendium of Physical Activities" is a widely recognized resource that lists MET values for hundreds of activities.
- Example: Brisk walking (3.0 mph) = 3.3 METs; Running (6.0 mph) = 10.0 METs; Cycling (10-11.9 mph) = 6.8 METs.
Measure Activity Duration: Record the exact duration you performed the activity, then convert it to hours.
- Example: 30 minutes = 0.5 hours; 45 minutes = 0.75 hours; 90 minutes = 1.5 hours.
Perform the Calculation: Multiply the MET value by the duration in hours.

Examples:

Moderate-Intensity Activity: You briskly walk (3.3 METs) for 45 minutes.
- Duration in hours = 45 minutes / 60 minutes/hour = 0.75 hours
- MET Hours = 3.3 METs × 0.75 hours = 2.475 MET hours
Vigorous-Intensity Activity: You run (10.0 METs) for 30 minutes.
- Duration in hours = 30 minutes / 60 minutes/hour = 0.5 hours
- MET Hours = 10.0 METs × 0.5 hours = 5.0 MET hours
Combined Activities: You cycle (6.8 METs) for 60 minutes and then do light stretching (2.3 METs) for 15 minutes.
- Cycling MET hours = 6.8 METs × 1.0 hour = 6.8 MET hours
- Stretching MET hours = 2.3 METs × (15/60) hours = 2.3 METs × 0.25 hours = 0.575 MET hours
- Total MET Hours = 6.8 + 0.575 = 7.375 MET hours

Limitations and Considerations

While MET hours are a valuable tool, it's important to acknowledge their limitations:

Individual Variability: MET values are averages. Actual energy expenditure can vary significantly based on individual factors like fitness level, body composition, age, sex, and environmental conditions. A highly fit individual might expend less energy for a given activity than a deconditioned individual.
Activity Specificity: The listed MET values represent typical effort for a given activity. For example, "weightlifting" has a range of MET values depending on the specific exercises, load, and rest periods.
Intensity Fluctuations: MET hours assume a constant intensity throughout the activity. In reality, many activities involve fluctuating intensities (e.g., stop-and-go sports, interval training), which can make precise calculation challenging without more advanced monitoring.
Does Not Reflect All Training Variables: MET hours primarily quantify energy expenditure volume. They do not directly account for other critical training variables like muscle damage, neuromuscular adaptations, or specific skill development, which are also vital for fitness and performance.

Conclusion: The Value of MET Hours

MET hours provide a robust and widely accepted method for quantifying the total volume of physical activity and its associated energy expenditure. By standardizing the measure of activity intensity (METs) and combining it with duration, this metric offers a powerful tool for:

Assessing adherence to physical activity guidelines.
Comparing the health benefits of different exercise regimens.
Facilitating large-scale research into physical activity and disease prevention.

For fitness enthusiasts, personal trainers, and students of kinesiology, understanding MET hours deepens the appreciation for the physiological demands of exercise and provides a more comprehensive framework for tracking and optimizing physical activity for health and performance.

METs (Metabolic Equivalents of Task) define the energy cost and intensity of physical activities, with one MET representing resting energy expenditure.
MET hours quantify the total volume of physical activity and energy expenditure by multiplying an activity's MET value by its duration in hours.
This metric is crucial for exercise prescription, public health recommendations (like WHO/CDC guidelines), and epidemiological research on physical activity and health outcomes.
Calculating MET hours involves determining an activity's MET value, measuring its duration in hours, and multiplying these two figures.
While valuable, MET hours have limitations, including individual variability in energy expenditure, the generalized nature of MET values, and the inability to account for fluctuating intensities or all training variables.

MET Hours: Understanding, Calculation, and Health Applications