It may sound daunting: The government says most adults should get 2 1/2 hours a week of physical activity that revs their heart rates.
But if you can't do that much, don't give up - every little bit helps, especially as people age.
"The message should always be to take it slow by setting realistic but challenging goals," says Jack Rejeski, Wake Forest University professor of health and exercise science. He recommends a walk with friends "and before you know it, you're through."
-The recommendation is for moderate-intensity physical activity, things like a brisk walk, water aerobics, cutting grass with a push mower, taking a dance class, doubles tennis.
-Just doing 10 minutes at a time counts. A few 10-minute activities each day add up.
-If you've been sedentary, build up gradually.
-If you prefer more vigorous activity - like jogging or singles tennis or a fast bike ride - the Centers for Disease Control and Prevention says 75 minutes a week is sufficient. One minute of vigorous activity counts for two minutes of moderate activity.
-The CDC says moderate-intensity means you're not breathing too hard to talk but you couldn't sing.
-In addition to the aerobic activity, the CDC urges muscle-strengthening activities at least two days a week. That can range from digging in the garden and yoga to push-ups or lifting weights.