According to the 2008 Physical Activity Guidelines for Americans healthy adults should do at least 150 minutes (2 hours and 30 minutes) a week of moderate-intensity, or 75 minutes (1 hour and 15 minutes) a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Aerobic activity should be performed in episodes of at least 10 minutes, and preferably, it should be spread throughout the week. Remember to start slow and be safe. This may mean you start out with 15 minutes of chair exercises each day and build up. If you are concerned about your health but want to start exercising, see a medical provider before beginning an exercise program.