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Exercise and Health

(original article May 2001; updated September 2002)

There are lots of reasons to exercise. The most important is that it is fun. There are also health benefits, some better documented than others. Those benefits supported by substantial or overwhelming evidence include the following:

The evidence also suggests that exercise lowers the risk of bowel cancer and it may lessen the extent of osteoporosis.

The question is how much exercise do you need to do, what type, and at what frequency?

In past decades, the exercise goal was set at achieving about 80 percent of your maximal heart rate. Now, the focus is on METs (metabolic equivalent tasks).

One MET is the energy expenditure and caloric requirement at rest. Mild exercise such as walking at a leisurely pace increases energy expenditure to perhaps 2.5 METs/hour of walking. Vigorous activity can result in 6 to more than 12 METs/hour of activity.

The following is a table of energy expenditure per hour of activity in METs (this is a general approximation; there is a lot of individual variation).

CLICK HERE for METs Charts

What should be the goal in MET-hours per week (METs per hour of each activity multiplied by hours per week of each activity). For weight control, relief of tension or stress, the MET hours per week goal is basically what works for you. For reduction in risk of heart disease, it is still not clear what the goal should be - a reasonable goal would be at least 12 MET-hours per week of moderately vigorous or vigorous activity. That could be accomplished by about four hours of brisk walking at a pace of one mile every twenty minutes (3.5 METs/hour). Whether average pace walking (one mile every 25 to 30 minutes) for four or five hours a week would be satisfactory is not yet clear, but there are some encouraging studies.

It might be a good idea for everyone to be METs conscious and to calculate the MET-hours of every leisure or work-related physical activity and keep a weekly record of MET-hours, assuming that a total of at least 12 MET-hours per week is a reasonable health promotion goal.

If you walk very briskly (one mile every 15 minutes) for 1/2 hour, that is 2.5 METs-hours. Play doubles tennis for one hour - maybe that’s worth 5 METs, depending on how much running you do. There is so much variation from individual to individual that all you can do is make a reasonable guess about MET values during exercising, but it still makes sense, and is sort of fun, to estimate MET-hours for each activity, set weekly goals, and try to reach them.

Some would say 6 to 8 MET-hours per week of moderately vigorous physical activity is enough to achieve substantial benefit; others would put the figure at 9 to 12; still others would argue 20 or even 30 MET hours/week of at least moderately vigorous activity is needed for reduction in risk of heart attack, diabetes, and some cancers.

There is no absolutely definitive figure. Thirty minutes of vigorous activity three times a week would result in at least 9 MET-hours (>6 METs per hour for vigorous activity divided by 2 for the 1/2 hour of activity, multiplied by 3 times per week). One hour of moderately vigorous activity, such as brisk walking, three times a week at 3.5 to 5 METs/hour would give 10.5 to 15 MET-hours. Although the evidence is convincing for the health benefits of moderately vigorous or vigorous exercise, it is less persuasive for less vigorous exercise or average pace walking (at least as far as heart attack prevention is concerned).

Still. the bottom line is that, if you cannot achieve the 12 MET-hours per week by moderately vigorous or vigorous activities or even by less vigorous activity done more often, do what you can. The evidence suggests reasonably strongly that doing something is better than being sedentary.

For example, walking for one hour at a leisurely to average pace, one mile every 25 to 30 minutes, three times a week is 3 to 2.5 METs each time or a total of 7.5 (one mile every 30 minutes) or 9.0 (one mile every 25 minutes) MET-hours a week. That may reduce risk of heart attack, especially in persons over 65 years of age. The least healthy situation appears to be that of being sedentary, and that appear to be more true for older age groups (over age 65). So, do what you can, taking into account your age, time constraints, and any underlying conditions. For those in older age groups or with underlying health conditions, it is a good idea to consult with your health care provider before undertaking any physical activity regimen.

Remember, although a reasonable goal is 12 MET-hours per week of at least moderately vigorous physical activity, if your age and any underlying condition permits, 20 to 30 MET hours of at least moderately vigorous activity is even better. Activities at home or at work count as much as recreational activities.

CLICK HERE for METs/hour intensity of home and occupational activities.

Here is the Healthful Life summary recommendation in regard to moderately vigorous (or vigorous) physical activity and lesser activities for those who cannot engage in moderately vigorous activities.

If you are over age 40 and moving from sedentary to physically active, or if you are substantially increasing the amount of your physical activity, it is a good idea to first consult your health care practitioner.