Would you walk 30 minutes every day to live a year longer?

That ‘s the starting benefit of moderate exercise.  You gain more if you do more strenuous exercise. 

Exercise is measured in METS.

METs – “metabolic equivalents” – are the way exercise physiologists compare energy used by a person doing different activities.  By definition, one “metabolic equivalent” (1.0 MET) equals sitting quietly for an hour.  At the other extreme, for example, running at a speed of 10 miles per hour is 18 METS (if you keep it up for a whole hour).  This means you use 18 times more energy to run at a speed of 10 miles per hour than to sit in a chair.

If the METs are multiplied by the number of minutes you do an exercise, they are called MET minutes.  For example, sitting for one hour is 1 MET energy expenditure for 60 minutes or 60 MET minutes.  Or, 3 METS an hour for 60 minutes equals 180 MET minutes (3 MET hours x 60 minutes/ hour = 180 MET minutes).  MET minutes can be added up to measure exercise for a whole week.

Note: an activity counts only if it is done for a minimum of 10 minutes or in an extremely intense short burst, such as a sprint race.  Doing something for 5 minutes does not have the same clear benefit because it does not make you breathe faster.

METs are measured by how much oxygen you use.

We need oxygen to extract energy from sugar and fat.  Physiologists determine energy use by measuring the oxygen a person uses as they breathe in and out during exercise.  To measure the oxygen a person uses, they measure the oxygen left in the air when the person breathes out.  The amount of oxygen the person used is the difference between what the person breathed in and what is left in the air when they breathe out.   

A person with normal lungs – and normal breathing response – can estimate the relative number of METS they are using by observing how hard or how fast they are breathing.  3.0 METS an hour means you can still carry on a conversation, but you are breathing hard enough that you can’t sing.  7.0 METS an hour means you are breathing hard enough that you can’t talk more than gasping a few words at a time.

MET minutes per week of exercise benefits longevity.

A team of researchers from Canada, Boston, Baton Rouge, and Columbia, South Carolina have used data from NHANES (National Health and Nutrition Examination Survey), the Health Interview Study, and US Life Tables to estimate 5-year survival according to how much a person exercises in their leisure time. 

They found that people who exercised regularly- but not enough to add up to 500 MET minutes per week – had some benefit [click for abstract].  People who did more exercise got more benefit.  As an approximation, 500 METs per week is equivalent to 2½ hours of moderate activity such as brisk walking, or 1¼ hours of vigorous activity such as running hard.

Caucasians and African Americans gained about 1 ½ to 2 years of life for being somewhat active every week (a little more for younger persons and a little less for persons over 60 years old).  If they exercise more than the basic 500 MET minutes per week, they will gain about an additional year.  For reasons that were not clear, neither Hispanic men nor Hispanic women gained life years from increased leisure time activity in this study, but there was no measure of how much activity they already had in their daily lives, so they may have been more active all the time.

Women who are active have a lower risk of getting breast cancer.

The Nurses Health Study previously found that women who get 9 MET hours per week or more of exercise – including those who start exercise after menopause – have about a 10 percent reduction in breast cancer [click here for complete article].   [9 met hours x 60 minutes per hour= 540 MET minutes, about the same as the 500 MET minutes that increases longevity].  Again, this is 30 minutes of brisk walking every day.  Note, if you walk briskly for 45 minutes, you can walk fewer days to get the same number of METs.  More intense exercise provides the same benefit in less time.

Calculate your METs per week.

There is a US Government website that discusses METs, but they only list a limited variety of examples [click here].  A year 2000 article in Medicine and Science in Sports and Medicine gives a wide variety of examples, but you need to pay for the whole article [click here for the abstract and the 2011 update]. 

To help you, I have selected representative activities and calculated the MET minutes for an hour and half an hour of each activity [click here].

To calculate the number of METs you personally expend in a week, list each activity, and how long you do it for.  You get credit for the intensity of each activity, but only for the length of time you do it.  For example, if you swim hard for an hour, that is 480 MET minutes (or 6 METs).  If you only do it for half an hour, that is 240 MET minutes, as in the table.  But if you only do it for 15 minutes, that is half of the 240 or 120 MET minutes. 

The health benefit you receive comes from the total of all of your leisure time activity.  If you swim hard for 30 minutes two days a week, that is 240 MET minutes x 2 or 480 MET minutes.  Suppose you also do an hour of Tai Chi for 240 MET minutes, and take a one-hour, brisk walk on Saturday morning for 228 MET minutes.  Your total would be 948 MET minutes or a total of 15.2 METs (948 MET minutes/ 60 minutes per hour = 15.2 METs) in that week.   

Again, note that you receive the basic benefits of 500 MET minutes a week by walking only 30 minutes per day. 

The benefits of vigorous activity also apply to men.