How to calculate METs by age: Understanding the Impact of Age on Your Exercise Intensity

The average resting metabolic rate declines by approximately 1% annually after age 60, directly impacting the energy cost of physical activity. Understanding how to calculate METs by age can provide a more accurate picture of your exercise intensity and calorie expenditure, helping you set more realistic and effective fitness goals. Standard MET values are often based on a baseline resting metabolic rate (RMR) that may not be accurate for older adults.

Quick Summary

This guide explains the foundational concept of METs and presents specific formulas used in clinical settings to predict age- and sex-adjusted MET values. It provides practical examples for personalizing exercise intensity, details how standard MET values may misclassify effort for different age groups, and offers a comparison table of exercise intensities.

Key Points

• Age Significantly Impacts METs: The standard MET value of 3.5 ml/kg/min for resting metabolic rate is not appropriate for all ages, particularly older adults, leading to potential misclassification of exercise intensity.

• Use Age-Adjusted Formulas: More accurate predictions for peak METs can be calculated using regression formulas developed in clinical settings, such as 14.7 - (0.11 x age) for men and 14.7 - (0.13 x age) for women.

• Older Adults Need Lower Targets: What is a moderate MET level for a younger person can be vigorous for an older individual, so setting age-appropriate fitness thresholds is crucial for safety and effectiveness.

• Correct Standard METs for Precision: For personalized tracking, standard Compendium MET values can be corrected by calculating an individual's unique resting metabolic rate (RMR) using equations like the Mifflin-St Jeor equation.

• Interpret MET Scores Contextually: A person's fitness level, health status, and age must be considered when interpreting what a MET score means for their personal goals.

• Focus on Relative Effort: Instead of universal MET benchmarks, focus on achieving a target MET level relative to your age- and sex-based standards to gauge performance accurately.

What are METs and why is age a critical factor?

A metabolic equivalent of task (MET) is a unit used to estimate the energy cost of physical activity. One MET is defined as the energy expended while sitting quietly at rest, which is standardized as an oxygen consumption of 3.5 ml/kg of body weight per minute. For example, an activity with a value of 4 METs requires you to expend four times the energy of sitting still. While the standard MET scale is useful, it doesn't account for individual differences in resting metabolic rate (RMR), which are significantly influenced by age and sex.

Research has shown that RMR declines with age, meaning the baseline energy expenditure for older adults is lower than the standardized 3.5 ml/kg/min. This can lead to a misclassification of exercise intensity, potentially underestimating the risk associated with low fitness in older individuals and overestimating it in younger, more active people. Clinicians and fitness professionals recognize that an individual’s maximal MET capacity naturally decreases as they get older. Therefore, assessing exercise capacity relative to age- and sex-based standards is more logical and accurate than using a single threshold for all adults.

Age- and sex-adjusted formulas for predicted METs

For a more accurate assessment of exercise capacity, clinical studies have developed specific regression formulas that incorporate age and sex. These formulas are often derived from treadmill stress tests, such as the Bruce protocol, and provide a predicted peak MET value for a person of a certain age.

Formulas for predicted peak METs

• For Men: Predicted METs = 14.7 - (0.11 x age)
• For Women: Predicted METs = 14.7 - (0.13 x age)

It is important to note that these equations were developed in clinical settings, and individual results can vary based on fitness level, genetics, and health status. However, they provide a much better benchmark than a one-size-fits-all approach.

Using corrected METs for a more personal estimate

The standard Compendium of Physical Activities provides fixed MET values for hundreds of activities. While convenient, these don't account for how an individual's unique resting metabolic rate (RMR) affects the actual energy cost. Researchers have proposed methods to correct these standard values, often using established RMR equations like the Mifflin-St Jeor equation.

How to correct a standard MET value

1. Calculate your RMR: Use an equation like the Mifflin-St Jeor equation to get a personalized RMR estimate.
   • Men: RMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5
   • Women: RMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161
2. Convert RMR to standard MET baseline: Divide your RMR (in kcal/day) by 1440 (minutes in a day) to get kcal/min. Then divide by 5 to get L/min of oxygen. Finally, divide by your weight in kg and multiply by 1000 to get ml/kg/min.
3. Adjust the activity's MET: Take the standard MET value from the Compendium and multiply it by 3.5 ml/kg/min (the fixed RMR standard). Then divide this number by your personal RMR baseline from the previous step. This provides a corrected MET for your activity.

This approach offers a more individualized estimate of your exercise intensity, though it is more complex than using standard lookup tables.

Why age matters in interpreting METs

Interpreting MET values requires context, and age provides crucial context. A 5 MET activity—such as moderate-pace elliptical training—will feel very different to a young athlete than to an older, sedentary individual.

For younger adults, a high MET capacity is normal. The focus is often on pushing into higher MET ranges (6+ METs) to achieve and maintain vigorous cardiovascular fitness. A plateau or decline might signal a need to increase intensity.

For older adults, a more conservative approach is necessary. Research has established age-specific fitness thresholds for risk assessment, showing that what is a moderate effort for a 50-year-old might be vigorous for someone in their 70s. For older adults, even small increases in METs achieved during exercise can have significant health benefits.

Comparison of MET interpretation by age

Feature	Young Adult (20-30 years)	Older Adult (70+ years)
Baseline RMR	Higher, closer to 3.5 ml/kg/min standard.	Lower, potentially 22–31% lower than the standard.
Predicted Peak METs	Higher, can reach 11–15 METs or more, depending on fitness.	Lower, often 5–6 METs at a healthy threshold, but can be improved.
5 MET Activity	Likely felt as moderate intensity.	Often perceived as vigorous intensity.
Cardiorespiratory Goals	Aim for vigorous activities (6+ METs) to boost fitness.	Focus on improving functional capacity to maintain independence; even moderate (3–5.9 MET) activity is highly beneficial.
Standard MET Interpretation	Standard values from the Compendium are often a good starting point.	Standard MET values may underestimate energy cost. Corrected MET values or clinical guidelines are more accurate.

How to apply METs for personalized fitness

Once you understand how age impacts your baseline and peak MET capacity, you can use METs to tailor your fitness routine. Here is a step-by-step guide:

1. Use Compendium Tables for general guidance: Refer to the Compendium of Physical Activities for a large table of standard MET values for various activities, from gardening to running.
2. Adjust expectations for your age: For older adults, recognize that a vigorous activity for you (e.g., 6+ METs) may not match the intensity of a younger person's vigorous activity. Interpret your effort level relative to what is healthy for your age group, not a universal standard.
3. Consider corrected METs for precise tracking: For more advanced tracking, especially for weight management, use a corrected MET formula that incorporates your specific height, weight, and age.
4. Prioritize overall activity, not just exercise: The benefits of high MET activities are clear, but daily movement also plays a significant role in overall health. Activities like standing instead of sitting can increase your energy expenditure by a notable percentage.
5. Consult a professional: For those with underlying health conditions, a healthcare provider can use a clinical exercise stress test to prescribe a safe exercise zone based on a precise MET capacity test. This is especially important for older adults or those with heart conditions.

Conclusion

While the concept of a metabolic equivalent is simple—a multiple of resting energy expenditure—the application is more nuanced when factoring in age. Standard MET values offer a practical starting point, but they fail to capture the significant decline in metabolic rate that occurs with aging. By using age- and sex-adjusted formulas and interpreting MET scores relative to age-specific standards, individuals can more accurately gauge their exercise intensity. This personalized approach is crucial for setting effective fitness goals, optimizing calorie expenditure, and safely building cardiorespiratory fitness across a lifetime. Whether using simple lookup tables or more complex corrected formulas, integrating age into your MET calculation provides a more realistic and actionable path toward better health.

One authoritative outbound link:

• Compendium of Physical Activities Tracking Guide

References

1. AHA Journals
2. ACE Fitness
3. JACC Journals
4. ScienceDirect
5. Healthline
6. Compendium of Physical Activities
7. National Institutes of Health (NIH)
8. ResearchGate
9. NASM Blog
10. Medscape Reference
11. WebMD
12. Omni Calculator
13. The Movement System
14. Howdy Health
15. Concordial University
16. GE HealthCare

Frequently Asked Questions

What is a metabolic equivalent (MET)?

A metabolic equivalent, or MET, is a unit of measurement that estimates the energy cost of physical activity. One MET is defined as the energy you use while sitting quietly at rest. An activity with a MET value of 4 means you are expending four times the energy you would at rest.

Why do standard METs need adjustment for age?

Standard MET values are based on a fixed resting metabolic rate (RMR) for the average adult. Since RMR naturally declines with age, the baseline for older adults is lower. Using standard values for older individuals can lead to underestimating the energy cost of their activities and potentially misclassifying intensity.

How can I get an age-adjusted MET calculation?

For an estimate of your peak MET capacity, you can use age- and sex-specific formulas developed in clinical research, such as 14.7 - (0.11 x age) for men and 14.7 - (0.13 x age) for women. For specific activities, you can correct the standard Compendium MET value using a personalized RMR calculation.

What is a 'good' MET score for my age?

A 'good' MET score depends on your age, sex, and overall fitness level. Instead of a single number, it is more accurate to assess your performance relative to age- and sex-based standards. For example, a healthy 50-year-old woman is expected to achieve a higher peak METs than a healthy 70-year-old woman.

How does exercise intensity differ for younger versus older adults?

A specific MET level, such as 5 METs, may be perceived as moderate intensity for a younger adult but as vigorous intensity for an older adult. Older adults have a lower peak MET capacity, and even moderate activity provides significant health benefits. Younger adults typically need higher MET levels to reach vigorous intensity.

Can I use METs to lose weight?

Yes, METs can be used to estimate calorie expenditure, which is vital for weight management. The formula METs x 3.5 x Body Weight (kg) / 200 = Kcal/min provides an estimate of calories burned. However, personal factors like age and body composition mean this is an estimate, and individual results will vary.

How can I use METs to personalize my fitness goals?

By understanding your age-adjusted MET capacity, you can set realistic intensity targets. For older adults, focus on improving functional capacity within a healthy range for your age. Younger adults can aim for higher MET activities to increase cardiorespiratory fitness. A fitness professional can help tailor a plan based on a MET capacity test.