For most healthy adults, the Department of Health and Human Services recommends that you get at least 150 minutes a week of moderate aerobic activity (brisk walking, mowing) or 75 minutes a week of vigorous aerobic activity (running, aerobic dancing). You can also do a combination of moderate and vigorous activity. The guidelines suggest that you spread out this exercise during the course of a week. The guidelines also recommend that you do strength training exercises at least twice a week. No specific amount of time for each strength training session is included in the guidelines.