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Phys Ed Gretchen Reynolds on the science of fitness.

Walking, fast or slow, is wonderful exercise. But now a first-of-its-kind study shows that to get the most health benefits from walking, many of us need to pick up the pace.

The findings stem from a new analysis of the National Walkers’ Health Study, a large database of information maintained at the Lawrence Berkeley National Laboratory about thousands of middle-age men and women who walk regularly for exercise. Recruited beginning in 1998 at walking events and from lists of subscribers to walking-related publications, these volunteers filled out a lengthy survey about their typical walking distance and pace, as well as their health history and habits.

As most of us would likely guess, walking is the most popular physical activity in America. But people who walk for exercise do so at wildly varying speeds and intensities. Some stroll at a leisurely 2 miles per hour, which is low-intensity exercise. Others zip along at twice that pace or better, resulting in a sweatier workout.

Exercise guidelines generally suggest that for health purposes, people should engage in 30 minutes of moderate-intensity activity most days of the week. For walkers, a moderately intense pace would probably be about 15 or 16 minutes per mile.

It has generally been assumed that if people walk more slowly but expend the same total energy as brisk walkers — meaning that they spend more time walking — they should gain the same health benefits. But few large-scale studies have directly compared the impact of moderate- and light-intensity walking, especially in terms of longevity.

To do so, Paul T. Williams, a statistician at Lawrence Berkeley National Laboratory, gathered data about 7,374 male and 31,607 female participants from the walkers’ health study, who represented almost every speed of fitness walker, from sluggish to swift. His findings were published online this month in PLoS One.

Dr. Williams divided participants into four numerically equal categories, based on their normal pace. Those in Category 1, the fleetest, averaged less than 13.5 minutes per mile, putting them on the cusp of jogging, while those in Category 4, the slowest, strolled at a relatively dilatory 17 minutes or more per mile. The majority of the walkers in this group in fact required at least 20 minutes to complete a mile, and many had a pace of 25 minutes or more per mile. (Interestingly, on average, female walkers were faster than men in all of the categories.)

Next, Dr. Williams cross-referenced his data against that in the essential if somewhat ghoulish National Death Index to determine which of the almost 39,000 walkers had died in the decade or so since they had joined the survey and from what.

It turned out that nearly 2,000 of the walkers had died. More telling, these deaths disproportionately were clustered among the slowest walkers. Those in Category 4 were about 18 percent more likely to have died from any cause than those in the other three categories and were particularly vulnerable to deaths from heart disease and dementia.

Unexpectedly, the death rate remained high among the slowest walkers, even if they met or exceeded the standard exercise guidelines and expended as much energy per day as someone walking briskly for 30 minutes. This effect was most pronounced among the slowest of the slow walkers, whose pace was 24 minutes per mile or higher. They were 44 percent more likely to have died than walkers who moved faster, even if they met the exercise guidelines.

One important inference of these statistics is that intensity matters, if you are walking for health. “Our results do suggest that there is a significant health benefit to pursuing a faster pace,” Dr. Williams said. Pushing your body, he said, appears to cause favorable physiological changes that milder exercise doesn’t replicate.

But there are nuances and caveats to that conclusion. The slowest walkers may have harbored underlying health conditions that predisposed them to both a tentative walking pace and early death. But that possibility underscores a subtle takeaway of the new study, Dr. Williams said. Measuring your walking speed, he pointed out, could provide a barometer of your health status.

So check yours, your spouse’s or perhaps your parents’ pace. The process is easy. Simply find a 400-meter track and, using a stopwatch, have everyone walk at his or her normal speed. If a circuit of the track takes someone 6 minutes or more, that person’s pace is 24 minutes per mile or slower, and he or she might consider consulting a doctor about possible health issues, Dr. Williams said.

Then, with medical clearance, the slow walkers probably should try ramping up their speed, gradually.

The most encouraging news embedded in the new study is that longevity rises with small improvements in pace. The walkers in Category 3, for instance, moved at a speed only a minute or so faster per mile than some of those in the slowest group, but they enjoyed a significant reduction in their risk of dying prematurely.