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In recognition of the risks of rampant inactivity, this year the federal Dietary Guidelines for Americans, which have been issued every five years since 1980, included its most explicit recommendations to date on exercise. The scientists who wrote the guidelines struggled to boil down a complex array of research findings. The results, alas, were somewhat baffling. Americans were advised to get 30 min. per day of moderate-intensity physical activity "on most days of the week," 60 min. per day if they were trying to control their weight and up to 90 min. per day to maintain weight loss. Even a temperate government scientist like Kohl admits that "there's a need to clarify that." And there seems to be a consensus on what the clarification should be. "The rock-bottom message should be 30 minutes a day, five days a week," says Church. And while 30 uninterrupted minutes are preferable, three 10-min. bursts also do the trick. As for what moderate means, Kohl offers this guidance: "Walking at about 3 to 3.5 miles per hour is moderate. If you can't maintain a conversation and your heart is beating rapidly, then you've probably crossed into vigorous."
How many Americans get a moderate 30 minutes at least five times a week? In a TIME survey of more than 1,000 randomly selected American adults, 33% said they do. Federal surveys suggest that it's more like 26%, although if you include data on activities such as gardening and cleaning, as opposed to just recreational exercise, the figure jumps to about 45%. In short, somewhere from a quarter to half of Americans say they get the recommended dose of exercise, although the lower figure may be more trustworthy. People are notorious for lying about their exercise habits or, as the CDC puts it, for overreporting "socially desirable responses." Says Church, more succinctly: "My experience asking questions about exercise: they suck!"
Church and many others believe there's a simple way for more Americans to get the activity their bodies need, and it doesn't require gym memberships or fancy equipment. The answer, they say, is walking. Unfortunately, most American communities were designed in the age of the automobile and aren't built for bipeds. "The U.S. probably has the lowest percentage of trips by biking and walking of any country," says psychologist Jim Sallis, director of the Active Living Research program at San Diego State University. Between 1977 and 1995, trips Americans made by walking declined 40%, even though a quarter of those trips are a mile or less. During the same period, walking to school fell 60%. By 2001 only 13% of trips to school were made by foot or bicycle.
Walking and physical motion have also been steadily drained from the workplace. Even a low-impact job like research librarian no longer involves much reaching, bending and pulling tomes from the stacks--not when you can let your fingers do the walking on a keyboard. To put modern society's lack of movement in context, researchers at the University of Tennessee's Department of Health and Exercise Science studied a group of Old Order Amish, a religious sect that shuns cars and other modern conveniences. Using pedometers, the researchers found that the average Amish man took 18,425 steps a day and the average Amish woman took 14,196 steps. A typical American, by contrast, takes about 5,000.