Decades of Admonitions Fail to Get Americans Moving
By GINA KOLATA
The finding was so serious that it could be comparable in its health effects to a vitamin deficiency, medical experts said. It was so shocking that U.S. News & World Report published a special 11-page section warning the nation.
"There is deep concern in high places over the fitness of American youth," the magazine's report began. "Parents are being warned that their children — taken to school in buses, chauffeured to activities, freed from muscle-building chores and entertained in front of TV sets — are getting soft and flabby."
The date of that report was Aug. 2, 1957.
Nearly 50 years later, the hand-wringing continues, but now it is compounded by concerns about an obesity epidemic. Public health experts say they do not know why their exercise exhortations have gone unheeded for so long, but they are gathering more evidence of the extent of Americans' inactivity and the health benefits that could accrue from even moderate exercise. The latest sallies appeared last week.
In a paper published on Thursday in The New England Journal of Medicine, Dr. Sue Y. S. Kimm of the University of Pittsburgh School of Medicine and her colleagues reported that girls became so sluggish in their teenage years that many barely moved at all. Black girls were even more sedentary than whites, they added, warning that the stage is being set for a lifetime of obesity and associated chronic illnesses like high blood pressure and diabetes.
Dr. Kimm followed 1,213 black girls and 1,166 white girls from age 8 or 9 until age 18 or 19, asking about their activity outside school.
As the years went by, many girls moved about less and less, until, by the time they were 16 or 17, 56 percent of the black girls and 31 percent of the white girls reported no activity at all.
"We don't know what they were doing — watching TV, talking on the phone. They could just be hanging out," Dr. Kimm said. But she added, she found their lack of activity alarming.
Others did too. "It certainly doesn't augur well for the future," said Dr. Steven N. Blair, who is director of research at the Cooper Institute in Dallas, a nonprofit foundation that studies exercise and health. He worries about the long-term health effects of such a sedentary life, especially in view of data indicating that women who get even a moderate amount of exercise have significantly less heart disease than those who are inactive.
Those data were reported in the same issue of The New England Journal, in a paper by Dr. JoAnn E. Manson, the chief of preventive medicine at Brigham and Women's Hospital in Boston and her colleagues. Their study involved 73,743 women ages 50 to 79; of them, more than 12,000 were nonwhite.
Those who walked briskly for at least two and a half hours a week had 30 percent less heart disease than those who were less active, the researchers report. More exercise was slightly better in terms of health, but almost all of the benefit was achieved simply by going from being sedentary to walking briskly for 30 minutes a day, or doing an equal amount of some other exercise, five days a week.
The findings are consistent with those from other studies that mostly focused on men. That led the American College of Sports Medicine and the Centers for Disease Control and Prevention to issue recommendations that men and women walk briskly for at least 30 minutes most days of the week or get an equivalent amount of exercise by other means, like running, swimming or bicycling.
The studies establishing the 30-minute threshold are not ideal, Dr. Blair said. To eliminate the possibility that healthier people exercise, rather than the premise that exercise makes people healthier, a study would have to assign people at random to exercise or not and then look at outcomes like deaths from heart attacks.
Such a study will never be done, Dr. Blair predicted. It would be too difficult to recruit and retain people and it could cost as much as a quarter of a billion dollars, he estimated.
And, he added, "some would argue that it is not even ethical," because one group of participants would have to agree to be sedentary when most medical experts think exercise is important for health.
Dr. Blair is doing a randomized study of 450 middle-aged and older women who are slightly overweight. The women are assigned to one of three exercise groups, with one group exercising slightly less than the recommended amount, one exercising at the recommended amount, and the third exercising slightly more. He is asking how indirect measures of health, like blood pressure and oxygen consumption, vary as exercise is increased from mild to moderate to more than moderate. The goal, he said, is to try to get an exercise dose-response curve, at least for these indirect indicators of benefit.
In the meantime, another group of medical experts, concerned with obesity, just issued its own exercise prescription, doubling the usual recommended amount.
The group, the Food and Nutrition Board of the Institute of Medicine, issued its advice last week as part of a report on the recommended dietary allowances for nutrients like carbohydrates, proteins and fats, as well as for fiber, fatty acids and cholesterol.
They wrote that they knew the number of calories that people burned in a day and they knew how many calories would be consumed if people followed their dietary advice. Sedentary people, they worried, would gain weight. That led them to conclude that people must do the exercise equivalent of an hour of brisk walking each day.
The group wrote that "30 minutes of regular activity is insufficient to maintain body weight in adults in the recommended body mass index range." So, it concluded, "to prevent weight gain as well as to accrue additional weight-independent health benefits of physical activity, 60 minutes of moderate intensity physical activity (e.g. walking/jogging at 4 to 5 miles per hour) is recommended in addition to the activities required by a sedentary lifestyle."
Dr. Blair, for one, is not convinced. Some people stay thin with no exercise. Others, like him, gain weight no matter what they do.
"I have run at least 45 minutes a day for 30-some years," Dr. Blair said, adding that he also watched his diet. And yet, he said, "I gained 25 pounds."
With pronounced individual variations in propensities to gain weight, Dr. Blair said, the evidence is insufficient, in his opinion, to say that 60 minutes of exercise a day is needed to prevent obesity.
But when it comes to heart health, he and others say, the evidence is convincing, if not compelling, that 30 minutes of brisk walking on most days gives most of the benefit that exercise can deliver.
"It's important that the public understand that exercise doesn't need to be strenuous, it doesn't need to be uncomfortable, it should not be onerous," Dr. Manson said. She cautioned, however, that many people overestimate how much exercise they get.
Dr. Manson suggests that people measure a course and time themselves, making sure they walk a mile in 15 to 20 minutes. "People may tend to overestimate their walking pace," she said. The goal, she added, should be to walk 10,000 steps a day. Many people, she said, are sure that they are doing at least that, until they put on a pedometer and discover that they actually are walking just 4,000 or 5,000 steps.
"I also make the point to my patients that casually strolling around the mall and window shopping will not produce these health benefits," Dr. Manson said.
Many medical experts still worry that their exercise message is being heard, but ignored, and that the pattern dates back at least to the call to alarm in the 1950's.
The report on American youth, described in the U.S. News article, led President Dwight D. Eisenhower to say he was shocked by the finding. In response, he established the President's Council on Youth Fitness. In 1968, it became the President's Council on Physical Fitness and Sports, with a mandate to promote exercise and fitness for Americans of all ages.
Yet today, noted Dr. William Haskell, an exercise physiologist at Stanford, many children still are inactive, many teenagers, as documented by Dr. Kimm, are virtually immobile, and just 25 percent of Americans meet national guidelines for 30 minutes of brisk walking or its equivalent most days of the week.
About half the population, Dr. Haskell said, is "active on a sporadic basis." As for rest, he said, "They are couch potatoes."
"At least we have a high level of awareness," Dr. Haskell said. Most people know what they should be doing, even if they do not comply. Part of the problem, he speculated, may be that public health experts have emphasized how easy it is: just a half hour a day, not even all at once, and it can be accomplished just by walking.
"That message has led a lot of people to say, `I already get 30 minutes a day,' " Dr. Haskell said. "But when you put monitors on them, they don't." He added, "unless they had a stressful period, their heart rates never get above 100 beats per minute," which is less than would be expected from walking briskly.
"We can't just throw up our hands and say, `We tried,' " Dr. Haskell said. He is convinced that one reason people are getting fatter is because they are so sedentary and because they don't know it, with many thinking they are moving more than they really are.
Dr. Haskell and others are undeterred, determined to keep trying to find a way to change Americans' exercise habits.
"Physical activity is as close as we've come to a magic bullet for good health," Dr. Manson said. "It's more difficult than popping a pill, but it's worth it."