One area of controversy has been how much exercise is enough to improve general health, reduce the risk of heart disease, and increase longevity. Meaningful studies on this topic are very difficult to perform because they require large populations of subjects and many years of data collection, and because poor health sometimes results in limitations to physical activity. Despite these difficulties, it is clear that regular exercise, along with a generally healthy lifestyle, is beneficial. One recent U.S. National Institutes of Health (NIH) panel suggested that as little as 30 minutes every day of purposeful, moderately strenuous physical activity-for example, rapid walking or lawn mowing-is sufficient to lower the risk of heart disease. There is no conclusive evidence to prove that an especially rigorous exercise routine, such as running many miles per day, as opposed to walking or jogging daily, will add years to a persons life.
Getting in Shape(健美)
Physical fitness is often defined in terms of four measurements: cardiovascular-respiratory function, body composition (the proportion of lean body mass in comparison to fat), flexibility, and muscular endurance and strength. Exercise is characterized in terms of four variables as well: frequency, intensity, duration, and mode. In planning an exercise program, it is important to take into account ones personal fitness objectives and the exercise regimen that will best meet those objectives.
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