Moderate Exercise: No Pain, Big Gains
Harvey Simon, MD
America is in the grip of an energy crisis. The rising costs and dwindling supplies of fossil fuels get all the press, but from a medical point of view, the real crisis involves human energy -- or the lack thereof. In the United States, and throughout the industrial world, insufficient exercise is a major cause of morbidity and mortality. In America, it is an important contributor to 4 of the 6 leading causes of death: heart disease, cancer, stroke, and diabetes. In all, a sedentary lifestyle accounts for some 250,000 premature deaths annually. That means that 12% of all the deaths in America are caused by sloth, as are 23% of our chronic illnesses. It's a staggering burden of death, disability, and expense, and it's all the more tragic because it's unnecessary.
Modern epidemiologic, clinical, and laboratory studies have been documenting the health benefits of exercise for nearly 50 years, but fewer than 25% of Americans get the exercise that they need. What accounts for the gap between theory and practice?
In part, we are victims of our own success. Before the industrial revolution, about a third of all the energy used in American agriculture and manufacturing was provided by human muscles; now, that contribution is minuscule. We don't exercise because we no longer have to.
Cultural preferences and economic pressures add to the problem. The average American adult spends 170 minutes a day watching TV and movies and 101 minutes a day driving, but less than 19 minutes a day exercising. Spectator is a kind word for it; we are truly a nation of couch potatoes.
Healthcare professionals can't do much about our entertainment industry, advertising empire, or economic imperatives. And even if we could turn back from the information age, few would want to. But we can, and should, deal with another set of barriers to healthful exercise. In fact, our profession has erected some of these barriers. The first is the confusing mix of exercise guidelines and recommendations; for example, the US Surgeon General currently advocates 30 minutes of moderate exercise a day, whereas the Institute of Medicine calls for 60 minutes a day and the 2005 Dietary Guidelines for Americans recommends 30-90 minutes a day. The second barrier has its roots in the very movement that puts exercise on the map, the aerobics revolution.
The Aerobics Doctrine
The scientific study of exercise blossomed in the 1960s and 1970s. Its principal research tool was the maximum oxygen uptake test, which measures the amount of oxygen taken up by the lungs, pumped by the heart, and delivered to the muscles during maximal exertion on a treadmill or bicycle ergometer. Improvements in the maximum oxygen uptake, or VO2 max, quickly became the gold standard for judging the efficacy of exercise.
Research in many labs demonstrated that optimal improvement in VO2 max depends on rather vigorous exercise. The best results come from exercise that is intense enough to raise the heart rate to 70% to 85% of its maximum, prolonged enough to sustain that intensity for 20-60 minutes continuously, and frequent enough to occur 3-7 times a week. The aerobics doctrine was born.
In 1975, the American College of Sports Medicine issued its first exercise guidelines. They called for all healthy adults to exercise at aerobic intensity (60% to 90% of maximum) continuously for 20-30 minutes at least 3 times a week. These standards were soon adopted with only minor modification by the American Heart Association and the US Department of Health, Education, and Welfare, and they remained in effect for more than 2 decades.
The aerobics doctrine gained acceptance just as Frank Shorter, Bill Rodgers, and Joan Benoit Samuelson showed that Americans could run. Running became the emblem of aerobic exercise, and the marathon was installed as the icon of success. Despite extraordinary individual achievements, however, the aerobics revolution did not succeed in getting our nation off its duff.
The aerobics doctrine inspired the few but discouraged the many. I was one of the lucky ones who discovered the benefits (and pleasures) of distance running. But I also was one of the guilty parties. On the basis of the data at hand and with the best of intentions, I proclaimed that the only way to benefit from exercise was to exercise aerobically. In many publications, both professional and popular, I wrote that golf was the perfect way to ruin a 4-mile walk -- but I was wrong.
The aerobics doctrine was based on sound studies that showed that aerobic training is required to build optimal aerobic fitness. Epidemiologic studies soon confirmed that fit people are healthy people, with a reduced risk for coronary artery disease, hypertension, stroke, and diabetes and a reduced mortality rate. These data remain valid today: Aerobic-intensity training is excellent for fitness and health.
Health Benefits of Moderate Exercise
Without contradicting the value of aerobics, new data show that it is possible to attain nearly all of the health benefits of exercise without attaining high levels of aerobic fitness. Moderate exercise is the way to do it. In this formulation, intensity is less important than the net amount of exercise, and intermittent exercise is as effective as continuous activity. In fact, golf is very beneficial indeed, as long as players walk the course and play 2-3 times a week.
For most people, aerobic exercise is daunting. Moderate exercise should be much more appealing and accessible, but the message has not yet produced results. Part of the problem, I think, is the lingering belief that moderate exercise is a distant second-best to aerobics, that walking is a pale imitation of running. I suspect that when most people think of exercise, be they healthcare professionals or other folks, they hear the distant voice of their old coach barking, "No pain, no gain." For the 100-yd dash, your coach was right, but for achieving and maintaining health moderate, painless exercise is extraordinarily beneficial.
Table 1 (appended below) summarizes 22 studies showing how moderate exercise influences the risk for cardiovascular disease and mortality. Encompassing more than 320,000 people from around the world, the studies are eye-opening.
Because all but one of the studies summarized in Table 1 (appended below) are observational studies, they cannot prove a cause-and-effect relationship between a particular physical activity and an observed benefit. Still, I think that it's highly likely that a causal relationship exists. Scientists have demonstrated clear health benefits of exercise in animal models. Randomized clinical trials in humans prove that regular exercise can produce a broad range of physiologic changes and improvements in risk factors (cholesterol, blood sugar, body fat, blood pressure, etc) that can be expected to improve health and reduce the risk for many diseases. Moreover, the large number of observational population studies from around the world suggest strongly that the biological plausibility of benefit is a clinical reality.
Although we don't have the advantage of randomized clinical trials that evaluate the effects of exercise on cardiac events and mortality in healthy people, 48 such trials have been conducted in patients with proven coronary artery disease. According to a meta-analysis of these studies, about half of the 8940 patients were randomly assigned to receive the best medical and surgical care available, whereas the others got the same standard of care plus enrollment in cardiac rehabilitation programs that were based on moderate exercise. The exercisers came out on top; in all, they enjoyed a 26% reduction in the risk for death from heart disease and a 20% reduction in the overall death rate. It's powerful evidence that exercise protects the heart -- and what's good for ailing hearts should be at least as beneficial for healthy ones.
If cardiovascular risk reduction was the only benefit of moderate exercise, it would still be vitally important for every physically able individual. But there are many other benefits. Exercise is an essential partner with diet for people who need to lose weight. And many observational studies also suggest that "no-sweat" exercise can help reduce the risk for stroke (by 21% to 34%), diabetes (16% to 50%), dementia (15% to 50%), fractures (40%), breast cancer (20% to 30%), and colon cancer (30% to 40%).[2,3]
If that's not enough to get Americans moving, consider that exercise is also the only known way to slow the physiologic changes associated with the aging process in humans. None of these benefits require aerobic intensity; in science, as in the fable, the tortoise will do very nicely indeed.
A 2005 analysis of data from the famed Framingham Heart Study reports that people who exercise regularly enjoy 3.7 years of additional life expectancy as compared with sedentary individuals. An intensity equivalent to walking at a pace of 17 minutes per mile was sufficient. And another 2005 study showed that moderate exercise (walking 8.6 miles a week at 40% to 55% of maximum) will even increase the VO2 max (although not to the same degree as aerobic training).
One of the barriers to getting our patients moving is the academic distinction between exercise (defined as formal structured activity designed to promote fitness) and physical activity (defined as everything else). In our busy world, most people do not believe that they are able to set aside time for formal exercise, especially intense workouts. In fact, the distinction is both arbitrary and misleading. Any physically active undertaking will contribute to health if it is part of an active lifestyle. Raking the lawn and cross-country skiing are at opposite poles of a single spectrum of benefit. For maximum protection, activities at the low end of the spectrum require more time than those at the high end, but they also are safer and less likely to produce injuries -- and the health benefits are remarkably similar.
What should we call the broad spectrum of activities that contribute to health? The familiar terms (aerobic, anaerobic, endurance, isometric, and isotonic) are not quite right. That's why I've proposed the term cardiometabolic exercise (CME) to emphasize the health benefits of everything from moderate activity to aerobic training, from washing the car to hitting the elliptical. And the term is meant to emphasize that even at the low end of the spectrum, exercise has major benefits for the cardiovascular system (coronary artery disease, hypertension, stroke, arrhythmias, peripheral artery disease, etc) and metabolism (body fat, glucose homeostasis and insulin levels, lipids, etc).
Coining a term is one thing, but setting realistic goals is another. Health professionals have access to a rich literature that evaluates the intensity of exercise in units, such as metabolic equivalent, kilojoules, and kilocalories. But to help patients (and their healthcare providers) understand the relative value of various activities, I've translated these units of measurement into a simple CME point system and assigned the points to various recreational and daily activities (see Table 2 appended below).
The CME system should help people set realistic individual goals instead of wondering what to make of "guidelines" that call for 30-90 minutes of exercise a day. For general health and gradual weight loss, aim for 150 points a day or about 1000 points a week. For faster weight loss, reduce dietary calories more sharply and/or aim for 300 CME points a day.
The system encourages people to view physically active tasks as opportunities, not punishments. Climbing stairs instead of riding the elevator is but one example of a healthful choice that incorporates exercise into the fabric of daily life. We should encourage our patients to choose whatever activities work for them as long as they get enough exercise to maintain good health. As people experience the subjective benefits of moderate exercise, some will go on to aerobic training or sports participation.
People with medical problems or special needs require additional screening and supervision; guidelines are available for health professionals and the public.
CME is the key to exercise for health, and many people will get extra benefit by adding exercise for strength, flexibility, or balance at home for just a few minutes a day -- not necessarily at a gym under the watchful eye of a trainer. In addition, a prudent diet is an essential partner in the lifestyle prevention of many of the chronic illnesses that plague industrial societies.
Medical science continues to make astounding advances, but it has taken the collective effort of many dedicated scientists to bring us back to the wisdom of Hippocrates: "If we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health."
Harvey B. Simon's, MD, FACP, newest book, The No Sweat Exercise Plan. Lose Weight, Get Healthy, and Live Longer, was published by McGraw-Hill in 2006.
For more information, visit : <http://www.health.harvard.edu/>
Table 1. No Pain, Big Gains: Some Recent Studies of Moderate Daily Activities
Table 2. CME Points for Selected Activities
CME = cardiometabolic exercise
Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School, Boston, Massachusetts; Physician, Department of Medicine, Massachusetts General Hospital, Boston, Massachusetts
Disclosure: Harvey Simon, MD, has disclosed no relevant financial relationships.
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