Nov. 13, 2000 -- Legs striding, arms pumping, I'm hustling down a long corridor at the Cooper Institute of Aerobics Research in Dallas, alongside exercise scientist Andrea Dunn, PhD. Her studies have helped make walking more than just a way to get from here to there; she and her colleagues have elevated it to a respectable form of exercise.
Today, Dunn has agreed to show me just how brisk a walk must be to count as a workout. I'm hoping that in the process she'll also help settle a growing debate in the field of exercise research: How hard and how long do you need to work out to stay healthy? The answer is still controversial. But new research is beginning to provide a clearer picture.
Brisk walking gained the status of exercise after a landmark 1989 Cooper Institute study came to a surprising finding: that people who were only moderately fit were significantly less likely to die of heart disease than those who never got off the couch. True, people who were super fit had the lowest death rates. But all their extra work gained them only a modest advantage -- 10% to 15% -- over the moderately fit group. The study, which followed some 13,000 men and women for more than eight years, was published in the Nov. 3, 1989, issue of the Journal of the American Medical Association.
Start of an era
The Cooper study, and others that followed, profoundly changed the thinking of many researchers. Many sports scientists came to believe that moderately intense physical activities such as walking, gardening, or cleaning house -- dubbed "exercise lite" -- could provide most of the health benefits of more conventional exercise. To lead author Steven Blair, PhD, and his colleagues, this meant that instead of exhorting people to strive for levels of exercise that most of them would never achieve, health professionals could urge their patients to engage in the kinds of exercise they might actually get out and do.
Even the U.S. surgeon general joined the ranks, issuing guidelines that encourage Americans to engage in "a minimum of 30 minutes of physical activity of moderate intensity (e.g., brisk walking) on most, if not all, days of the week." The era of "exercise lite" had begun.
Walking shoes became the rage. A magazine called Walking was born. And hoofing it through the neighborhood became the exercise of choice for many active Americans.
Not just a walk in the park
But a decade after the famous study's release, some researchers argue that we've been sold a bill of goods. "Exercise lite is to exercise what lite beer is to beer. It's pretty bland stuff," says Paul Williams, PhD, an exercise scientist at the Life Sciences Division of the Lawrence Berkeley Laboratory in California. "Exercise lite has given many Americans a false sense that a stroll through the neighborhood is all you need to stay healthy. Instead of pushing people to be more active, it's given them an excuse to do as little as possible."
One recent study, appearing in the June 30 Mortality and Morbidity Weekly Review, offers some support for Williams' contention. The researchers surveyed people who walk for exercise and found that only 26% walked briskly enough to achieve the "moderate intensity level" recommended by the U.S. surgeon general. In addition, a mere 34% walked the recommended four times or more a week.
Williams' studies at Lawrence Berkeley Laboratory suggest that the real health payoff comes to exercisers who crank up both the intensity and duration of a workout. In ongoing research with 55,000 runners from around the country, Williams has found that the more miles runners cover -- up to a very rigorous 40 miles a week -- the lower their risk of heart disease.
"The more exercise you do, and the more vigorous it is, the more you benefit," says Williams, whose findings were published in the January 1997 issue of Archives of Internal Medicine.
How hard is hard?
So how strenuous should exercise be? How long is the ideal exercise session? And how many minutes of exercise should we strive for each week?
This is still the subject of intense debate. But two new studies should help provide better guidelines. Advocates of exercise lite have long argued that you can piece together 3 or 4 shorter sessions of 10 or 15 minutes of activity and get the same benefits as a sustained hour workout -- and it seems they're right. In a study published in the September issue of Circulation, researchers surveyed more than 7,000 men. Those who said they typically worked out in several short sessions of about 15 minutes were assessed as being just as healthy as those who did their exercise in one long session.
What appeared to matter, the study found, was how vigorously people exercised and the total amount of time they spent doing it. Therefore, anyone who wants to lower their risk of heart disease may need to fulfill the surgeon general's recommendation of exercising a minimum of 30 minutes at moderate intensity for at least four days of the week, in any cumulative combination.
Pick up the pace
If you're a lounge lizard whose idea of exercise is picking up the remote control, then walking a little every day will make you healthier and increase your odds of living a long life. But don't think you can shuffle along and call it exercise.
"When we say brisk, we mean brisk," says Andrea Dunn, her arms pumping as she powers her way down the corridor as I hurry alongside to keep up. "We're talking about walking fast enough to cover at least three and a half miles an hour. A brisk walk is the way you'd walk if you were hurrying to catch a bus or to get in from the cold. It's walking fast enough so that you begin to feel winded."
If walking is your exercise of choice, Dunn recommends mapping out a one-mile course. (You can drive the route in your car using the odometer or walk around a track at the local high school.) Then clock yourself while walking one mile. If you cover the distance in 15 minutes or less, you're walking briskly. "Believe me, we're not talking about strolling down the boulevard," says Dunn, sounding just a tad winded herself. "And we're not talking about stopping to smell the roses."
Peter Jaret, a freelance writer based in Petaluma, Calif., has written for Health, Hippocrates, and many other national publications. He is a contributing editor for WebMD.