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How Much Exercise Do I Need?

When it comes to exercise, less is not more-but it's certainly better than none. Physical inactivity accounts for as many as 23 percent of all deaths from major chronic (慢性的) diseases, yet almost one of every three Americans is sedentary (spending a lot of time sitting down). According to the Centers for Disease Control, 29.4 percent of those surveyed (调查) report they have no free-time physical activity at all. City people tend to be more active than country folks, with 27.4 percent saying they are sedentary, compared with 36.6 percent of those in rural areas.

Light activity can improve physical and mental well-being. While light activity is good, moderate (not very large or very small) activity is even better, and health experts encourage everyone to have at least 30 minutes a day of moderate physical activity. But you don't have to head to a gym. As recent studies have confirmed, "lifestyle" activities, such as walking, house cleaning and gardening, are as effective as a structured exercise program in improving heart function, lowering blood pressure and keeping or losing weight.

In one study, overweight, sedentary middle-aged men and women who learned behavioral skills to make them more physically active, such as walking around airports or train stations while waiting for a departure, reduced their body fat percentage and improved their blood pressure and heart function as much as individuals participating in structured programs at a fitness center. In another study, fat women ranging in age from 21 to 60 who adopted a more active lifestyle lost as much weight as women in a low-impact aerobics (有氧健身) program-and regained fewer pounds in the following year.

Recognizing the value of different levels and types of activity, the American College of Sports Medicine has changed its recommendations on quantity and quality of exercise to include flexibility as well as aerobic and muscle exercise and to acknowledge that multiple short periods of exercise during the day are nearly as beneficial as one long session.