What Are Metabolic Equivalents (METs)?

Training at the correct intensity is an important part of any successful exercise program. Not only does it allow you to properly optimize overload in a safe and effective way, it also allows you to avoid excessive training outcomes.

As one of the most underused units of intensity measurement, metabolic equivalents or METs provides useful information about the difficulty of your exercise session. Alongside maximal heart rate percentage, relative oxygen uptake values and heart rate reserve, METs form another piece of the jigsaw when it comes to effective programming.

But what are METs and why should you incorporate them into your training?

Let’s find out…


What are METs?

All physical activities require energy. Whether it’s standing up out of a chair to stretch your legs, or sprinting up a hill as part of pre-season training, all muscular work requires energy.

Metabolic equivalents (METs) are a measure of metabolic cost – a physiological benchmark used to track exercise intensity. You’ve might have them as a measurement on the console of a treadmill or bike?

METs are classified as the ratio of metabolic rate (as expressed as rate of energy consumption) against a given physical activity task – walking, weightlifting, yoga, gardening etc.

“One MET is defined as the amount of oxygen consumed while sitting at rest and is equal to 3.5 ml of O² per kg body weight, per min” [1]

One MET is essentially the amount of energy produced relative to body mass whilst at rest. As you sit here now reading this article you are expending 1 MET of energy.

For the average person, this equates to around one calorie per 2.2 pounds of body weight per hour. So if you weighed 180 pounds, 1 MET would burn around 80 calories per hour whilst at rest.



Measuring Physical Activity Using METs

METs provides an accessible method of measurement of physical activity both in and out of the gym. They describes the functional capacity or exercise tolerance of an individual against a pretty comprehensive pre-determined amount of data..

The metabolic equivalent is the energy expended compared to rest so it indicates the intensity relative to 1 MET. What this means is that an activity with a MET value of 6 shows that you are expending 6 times the energy (as measured in number of calories) than you would at rest.

The Compendium of Exercise

There are a number of pre-determined reference lists detailing MET values for different physical activities. One of the most detailed and comprehensive (and one that I’ve used in lectures many times) is called the Compendium of Physical Activities [2].

As you can see from the short excerpt below (the actual document is huge), each exercise or activity is characterized by how hard it is in METs.


Image result for metabolic equivalents for common physical activities


Using METs to Program Exercise

A good starting point to programming exercise and physical activity using METs is this brief table:

  • <3.0 METs = Light intensity
  • 3.0 – 6.0 METs = Moderate intensity
  • >6.0 METs = Vigorous

So using 1 MET as the reference value, light activities burn up to 3 times as many calories as rest, moderate activities burn 3-6 times as many and vigorous exercise turns over more than 6 times as much energy as rest.

The beauty of using this easy-to-reference- table is that you can prescribe general activity with more context. If you were a trainer and wanted your client to be active on days they weren’t seeing you, you could prescribe 20-30 minutes of a 5.0 MET activity of their choice for example.

To give you an idea of context (using the Compendium of Exercise as a guide), walking slowly has a value of 2.0, mowing the lawn comes in at 5.5 and cycling at 14-15 mph measures 10.0 METs. It’s just another way to measure overall activity load in a given week.

Image result for metabolic equivalents for common physical activities


The ACSM Guidelines

Of course, one criticism of METs is that at face value it doesn’t take into account differing capabilities. For example if you take a sedentary individual and a trained cyclist, the energy expenditure exercising on a bike at 14-16 mph will be completely different for each person. And this is where the ACSM guidelines come in.

If you’re familiar with the American College of Sports Medicine you’ll know that as an expert collaborative body they are responsible for providing the general public with safe and effective exercise prescription guidelines .

That way we know exactly what frequencies, intensities and duration of exercise we should use for each type of client and goal.

Current MET recommendations from the ACSM

Not only do current ACSM guidelines provide recommendations for exercise intensity in terms of percentages of HRM and rate of perceived exertion, they also provide MET values too.

Maximal Oxygen Uptake and METs

If you really want to get the best out of metabolic equivalents then you need to find a starting point. And where facilities and resources allow, that means finding your maximal oxygen uptake – otherwise known as your V0²max.

V0²max, similar to metabolic equivalents is a measure oxygen consumption. But rather than it being at rest like 1 MET (which for argument’s sake we’ll say is the minimum oxygen consumption level), it measures the maximum amount of oxygen you can consume.

Remember  that 1 MET is the equivalent of 3.5 ml.kg.min. Well let’s say that after performing a V0²max test your maximal oxygen uptake comes out at 65 ml.kg.min, which is pretty good for most people (notice how it’s measured using the same methods – ml.kg.min), all we have to do is work out how many METs that is.

So all we do is take 65 and divide it by 3.5. Were left then with 18.5.

This means that the maximum (in terms of oxygen consumption) that this person can work is 18.5 METs. Using the Compendium of Exercise table this is the equivalent of running at around 15 kph – hard work!

And now we’ve got the maximum METs can start to look at prescribing exercise.



V0²R and METs for Exercise Programming

If you take a look at the ACSM guidelines, you’ll notice that they make recommendations for cardiovascular performance exercise based on V0²R or V0² reserve.

For example, the ACSM suggest that you should work at >60% V0²R to improve cardio fitness. As a measure of training intensity, V0²R provides a more accurate estimate of actual exercise intensity than maximal oxygen uptake precisely because it takes rest into account.

How do you work your V0²R out though?

Well firstly your V0²R is simply your V0²max minus your resting V0² (3.5). In the case of our example, their V0²R comes out at 61.5 ml.kg.min. And 60% of that figure is 37 ml.kg.min.

V0²R = V0²max – 1 MET

Okay so what next?

Well unless you’ve got a way of measuring your VO² during exercise, the best thing to do is to use METs. How? Take 37 and divide it by 3.5. This gives us 10.5 METs.

All we do now is prescribe exercise for the workout at that MET value. Next time the client is on the bike or treadmill we flick to the METs value and get them to work at 10.5. That way we ensure that training overload can take place.


Take Home Points

  • You can prescribe MET intensities based on relative percentage of V0²R. This requires you conduct a maximal oxygen uptake test first.
  • You can prescribe general physical activity outside of the gym based on METs. You can base this on either low, moderate or vigorous categories using the Compendium of Exercise.

References

  1. Jetté, M et al. Metabolic equivalents (METS) in exercise testing, exercise prescription, and evaluation of functional capacity. Clin Cardiol. 1990; 13(8): 555-65
  2. Ainsworth, BE et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Med Sci Sports Exerc. 2011; 43(8): 1575-81

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