Walk More—That’s all you have to do

For cardiovascular and other health benefits like increased longevity, you need only exercise moderately for 30 minutes at least five days a week. That has been the recommendation for nearly 15 years, and it has decades of high-quality research to back it up. In an attempt to refine things further, a team of researchers asked the questions: Can this exercise recommendation be cut back further and still produce health benefits? Will 45 minutes five days of the week provide even more?

The study designed to answer these questions drew participants from the most sedentary segment of the U.S. population—postmenopausal women. Published last year in the Journal of the American Medical Association, this study continues to produce surprise findings as researchers are still analyzing the mountains of data it has generated.

A co-author of this and many other landmark studies is exercise scientist Steven N. Blair, PED, professor in the Department of Exercise Science at the University of South Carolina. One of the world’s leading researchers on the health benefits of exercise, Dr. Blair is interviewed by Maryann Napoli.

MN: Is it fair to summarize your research as providing proof that people can be fat and fit and that they can achieve cardiovascular fitness with only a moderate degree and amount of activity?

SNB: Scientists try to stay away from using the word “proof”, but we have provided pretty compelling evidence that you can be fat and fit—just as you can be thin and unfit. And that fitness provides important protection from many chronic diseases and premature mortality even in people who are obese.

MN: And it need not be vigorous exercise.

SNB: To attain what we’ve labeled “moderate fitness”—that is, if one follows the recommendation of 30 minutes of moderate intensity activity, such as walking on five or more days a week, you will develop a level of fitness that is protective.

MN: Must it be done in 30 consecutive minutes?

SNB: You can do it in separate segments—in bouts of at least ten minutes or more. The evidence for that has accumulated since we first made that recommendation back in the mid-1990s. It’s clear that whether you do 30 minutes of walking in three ten-minute bouts or two 15-minute bouts or all at once, the physiologic benefits are identical.

MN: That would also cut down on injuries.

SNB: It’s clear from our studies—and those of others—that as the amount and the intensity of the exercise goes up, the risk of injury does as well. The injury rate associated with moderate-intensity activity is incredibly low.

MN: How fast should people walk?

SNB: Walk purposefully as if you were going to a meeting—about 3 miles per hour, or 20 minutes a mile—but that will vary a bit depending on a person’s age, fitness, and health status. Some will need to walk a bit slower, especially when starting a program, and more fit individuals may walk at a faster rate.

MN: Why is it that those cardiac risk calculators that doctors use to determine an individual’s chance of having a heart attack in the next ten years do not include a question about physical activity? I’m referring to “risk assessment tools” like the one from the National Heart, Lung and Blood Institute that ask questions about blood pressure, cholesterol, etc. to identify who should be on drug therapy.

SNB: That calculator is largely based on the Framingham Heart Study [initiated 60 years ago], and they have never incorporated fitness. I tell physicians if you use the Framingham risk score to characterize your patients’ risk, you’re not finished with the job, unless you also have a measure of fitness or at very least, take a careful physical activity history.

MN: Why do you think the public continues to be told that excess weight will cause premature death and heart attacks? Three years ago, researchers at the Centers for Disease Control and Prevention (CDC) published a study that showed people who are overweight or even obese do not have shortened life spans. Decreased mortality was shown only at either end of the spectrum—the morbidly obese and the very thin.

SNB: Some people are dedicated to a concept that being overweight is hazardous to your health and they have an unwillingness to look at the actual data. When you look at the work of Katherine Flegal who headed that CDC study, you will see that she found that overweight is not the hazard for mortality as it has been made out to be, and it may even be protective. She used the best available data, such as that from the National Health and Nutrition Examination Surveys, which are broadly representative of the U.S. population. Yet there are people who have been vehement in their unrelenting criticism of Katherine and her work.

MN: Your work is focused on cardiovascular benefits, but weight loss motivates most people to exercise. I want to talk about a weight-related finding from your latest study that included 464 postmenopausal women who were sedentary, overweight or obese but basically healthy when they were randomly assigned to one of three exercise groups or the control group. This finding surprised me: After six months, “There were no differences in weight or body fat percent across the groups at follow-up but waist circumference was significantly smaller in all three exercise groups compared with the control [no exercise] group.”

SNB: That finding was not a surprise to anyone who works in this area. My colleague Bob Ross from Queen’s University in Kingston, Ontario has done more work on exercise and visceral adiposity than just about anyone. Bob said, “If you get people exercising, the visceral fat is going to go.” What we saw [in our study] was no difference in weight change across those four groups, yet all three exercising groups lost waist circumference, presumably visceral fat, compared with the control group.

MN: It should be pointed out here that one important aspect of your study is the fact that the women in the exercise groups performed their exercise routines under observation in the laboratory, thus bypassing the unreliable self-reporting that so often characterizes physical-activity studies. Your study measured what researchers call “dose response,” i.e., whether any health benefits were gained or lost by going lower or higher then the standard recommendation of 30 minutes five days a week of moderate exercise. Any other surprises?

SNB: I was a little surprised that the high-dose exercise group [225 minutes of exercise a week] did not lose more weight because they were doing three times the amount of exercise per week as the low-dose exercise group [72 minutes a week].

MN: What are you working on now?

SNB: We continue to analyze data from our study. When we looked at weights that were measured weekly in all the women, there are some fascinating findings there that I cannot talk about because we have not yet published our findings. It’s based on the notion promoted by the U.S. dietary guidelines 2005, which state, in order to prevent weight gain or promote weight loss, 60 minutes of activity a day is needed. Others have been trumpeting similar ideas. Well, if that’s the case, then the women in our high-dose exercise group should have lost a good bit more weight than the women in the lowest exercise group. We didn’t see that.

MN: Any idea why?

SNB: I’m not sure we’re ever going to know, but it is an area of research that cries out for more study—to try to understand where exercise fits in relation to weight management.

MN: The exercising study participants may not have lost weight, but regular testing of their cardiovascular/respiratory fitness during the study showed that they improved according to the amount of exercise they were assigned to perform.

SNB: Yes. As you see from our study there was a strong positive dose-response relationship for VO2 peak across the control and the three doses of exercise. Even the women in the lowest exercise group significantly improved their cardiovascular/respiratory symptoms and they only did 72 minutes of moderate intensive exercise a week. I’m coming to the conclusion that doing anything is better than nothing. I should be standing up right now while I’m talking with you.

MN: The blood pressure reductions in all three exercise groups were pitifully small.

SNB: Yes, I had expected exercise to show a dose-response gradient for blood pressure.

MN: You mean that you had expected the women doing the highest amount of exercise to have larger reductions in blood pressure.

SNB: Yes, the women were mildly hypertensive at the start of the study but all the exercise groups lowered their blood pressure only a few millimeters of mercury.

MN: There are still many proponents of vigorous-intensity exercise out there. I read that you used to be one of them until your own studies showed the health benefits of moderate-intensity exercise. I also read that you continue to enjoy running. Do you think that one day researchers will find that there are more health benefits to be gained with an intensive exercise routine?

SNB: Perhaps there might be some additional health benefits shown for vigorous exercise, but I frankly think the jury is still out on that one. I’m willing to go out on a limb here and say that doing something is better than doing nothing.

Maryann Napoli, Center for Medical Consumers ©

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