I’ve had too many discussions with patients about exercise that go like this:
Doctor: How much are you exercising?
Patient: I’m not. Too busy.
To avoid this stalemate, I think it’s helpful to think about what we mean by exercise.
Patients often equate exercise with intense physical activity: running, spinning, weight lifting, tennis. This sort of exercise makes you sweat and requires a change of clothes and a shower. It’s often hard to fit into a workday.
I think it is helpful to consider exercise in terms of the Met, or metabolic equivalent, which shows the energy cost of activities, in kcalories/kilograms/hour. Sleeping uses 0.9 Mets, sitting 1.0 Mets.
So for a 70 kg person (154 lbs), one hour of sitting would use 70 kcalories. 24 hours of sitting would use 70 x 24=1680 calories.
The Compendium of Physical Activities lists the Mets for numerous activities:
Considered this way, whenever you’re not sitting or lying down, you’re exercising, since you are burning more calories than you use at rest. Whenever you get up out of your chair, you are exercising.
The question then becomes not whether you exercise, (since unless you’re on bed rest, you exercise every day), but how much you exercise.
This can be measured in two ways: by how many minutes/day one spends in moderate intensity activities (walking is the classic example), or by how many steps/day one takes.
This is easily measured by movement sensors such as pedometers, or exercise monitors (the Fitbit One is my personal favorite), phone apps, etc.
The CDC currently recommends that all adults spend a minimum of 150 minutes/week in moderate intensity exercise, or 75 minutes/week in vigorous intensity exercise. Moderate intensity exercise is done at 3.0-5.9 times the intensity of rest, or 3.0-5.9 Mets. Vigorous intensity exercise is > 6.0 times the intensity of rest, or greater than 6.0 Mets.
More benefit comes from doubling those numbers: 300 minutes/week of moderate, or 150 minutes of vigorous, or some mix of the two.
Two days/week of muscle strengthening exercises to prevent muscle atrophy are also recommended.
Vigorous exercise is more time efficient in the short run (one gets one’s exercise done in half the time), but it carries a higher risk of injury, hence may be less sustainable in the long run.
But is vigorous exercise “better” for you than moderate exercise? Or is moderate exercise sufficient to get all the benefits of exercise? I’m not sure what is the correct answer, or if data exists that can answer this.
An interesting line of research has suggested that time sitting is not good for your health: increased rates of death, both all cause and specific (colon cancer) correlate with the number of hours one sits in a day. This suggests the benefits of simple activities that interrupt sitting, such as getting up and taking a walk around the office or the block, or going to the kitchen to make a cup of (green) tea.