Moderate exercise: No pain, b... Health Article

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 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 disability and death. In America, it is an important contributor to four of the six leading causes of death: heart disease, cancer, stroke, and diabetes. In all, sedentary living accounts for some 250,000 premature deaths annually. That means about 10% of all the deaths in America are caused by sloth, as are about 23% of our chronic illnesses. It's a staggering burden of illness, death, and expense, and it's all the more tragic because it's unnecessary.

Scientific studies have been documenting the health benefits of exercise for decades, but fewer than 25% of Americans get the exercise 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 television 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.

The medical profession can't do much about America's entertainment industry, advertising empire, or economic imperatives. And even if we could turn back from the information age, few would want to. But doctors can, and should, deal with another set of barriers to healthful exercise that they have erected themselves. The first is the confusing mix of exercise guidelines; for example, the surgeon general advocates 30 minutes of moderate exercise a day, while the Institute of Medicine calls for 60 minutes and the 2005 Dietary Guidelines for Americans recommend 30 to 90 minutes. The second barrier has its roots in the very movement that put exercise on the map, the aerobics revolution.

The aerobics doctrine

The scientific study of exercise blossomed in the 1960s and '70s. Its principal research tool was the maximum oxygen uptake test, which measures the amount of oxygen sucked up by the lungs, pumped by the heart, and delivered to the muscles during maximal exertion on a treadmill or stationary bicycle. 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 the VO₂ max depends on vigorous exercise. The best results come from exercise intense enough to raise the heart rate to 70% to 85% of its maximum, prolonged enough to sustain that intensity for 20 to 60 minutes, and frequent enough to occur three to seven times a week. The aerobics doctrine was born.

In 1975, the American College of Sports Medicine issued its first exercise guidelines, calling for all healthy adults to exercise at aerobic intensity (60%–90% of maximum) continuously for 20 to 30 minutes at least three times a week. These standards were soon adopted with only minor modification by the American Heart Association and the U.S. Department of Health, Education, and Welfare, and they remained in effect for more than two decades.

Unintended consequences

The aerobics doctrine gained acceptance just as Frank Shorter, Bill Rodgers, and Joan Benoit Samuelson showed that Americans could run, so 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. A relatively small number of lucky people discovered the benefits (and pleasures) of aerobic exercise. But based on the data at hand and with the best of intentions, doctors discouraged people who found aerobics too hard from getting moderate exercise by proclaiming that aerobic intensity was essential for benefit. For example, the Gospel of Aerobics preached that golf was the perfect way to ruin a four-mile walk, but we now know that's wrong.

Fitness vs. health

Sound studies showed that aerobic training is required to build optimal aerobic fitness. Epidemiological studies soon confirmed that fit people are healthy people, with reduced risks of coronary artery disease, hypertension, stroke, and diabetes, and a reduced mortality rate. These data remain valid: Aerobic training is excellent for fitness and health.

Without contradicting the value of aerobics, studies show that it is possible to get nearly all the health benefits of exercise without reaching high levels of aerobic fitness. The answer is moderate exercise. 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 two to three times a week.

The benefits of moderate exercise

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 is the lingering belief that it's a distant second best to aerobics — that walking is a pale imitation of running. When most people think of exercise, be they health care professionals or other folks, they hear the voice of their old coach barking, "No pain, no gain." For the 100-yard dash, your coach was right — but for health, moderate, painless exercise is extraordinarily beneficial.

Table 1 summarizes 22 studies that show how moderate exercise influences the risk of cardiovascular disease and mortality. Covering more than 320,000 people around the world, the studies are eye-opening.

Because all but one of the research publications summarized in Table 1 are observational studies, they cannot prove a cause-and‑effect relationship between a particular activity and an observed benefit. Still, it's highly likely that a causal relationship exists. Scientists have demonstrated the clear health benefits of exercise in animal experiments. Randomized clinical trials in humans prove that regular moderate exercise can produce a broad range of improvements in risk factors (cholesterol, blood sugar, blood pressure, body fat, etc.) that can be expected to improve health and reduce the risk of many diseases. Moreover, the large number of observational population studies done around the world suggests strongly that the biological plausibility of benefit is a clinical reality.

Although we don't have the advantage of randomized clinical trials to evaluate the effects of exercise on cardiac events and mortality in healthy people, doctors have performed 48 such trials in patients with proven coronary artery disease. About half of the 8,940 patients were randomly assigned to receive the best medical and surgical care available; the others got the same standard of care plus enrollment in cardiac rehabilitation programs based on moderate exercise. The exercisers came out on top; in all, they enjoyed a 26% reduction in the risk of 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 were the only benefit of moderate exercise, it would still be vitally important for every physically able individual. But it has many other benefits. Exercise is an essential partner with a healthy diet for people who need to lose weight. And many observational studies also suggest that "no sweat" exercise can help reduce the risk of stroke (by 21%–34%), diabetes (16%–50%), dementia (15%–50%), fractures (40%), breast cancer (20%–30%), and colon cancer (30%–40%). If that's not enough to get Americans moving, consider that exercise is also one of the two available ways to slow the physiological changes associated with aging; severe caloric restriction is the other. None of these benefits requires 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 when 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%–55% of maximum) will even increase the VO₂ max, though not to the same degree as aerobic training.

Cardiometabolic exercise

One of the barriers to getting people moving is the academic distinction between exercise (formal structured activity to promote fitness) and physical activity (everything else). In our busy world, most people do not feel they can 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. Activities at the low end of the spectrum require more time than those at the high end, but they are also 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 usual scientific words (aerobic, anaerobic, endurance, isometric, isotonic) are not quite right. That's why we've proposed the term cardiometabolic exercise (CME) to emphasize the health benefits of everything from moderate activity to aerobic training, from washing the car by hand to hitting the elliptical. And it 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, blood sugar and insulin levels, cholesterol, etc.).

Coining a term is one thing, setting realistic goals another. Health professionals have access to a rich literature that evaluates the intensity of exercise in units such as METs, kilojoules, and kilocalories. But to help real people understand the relative value of various activities, we've translated these measurements into a simple CME point system. Table 2 shows some examples of "CME points."

The CME system should help you set realistic individual goals instead of wondering what to make of "guidelines" that call for 30 to 90 minutes of exercise a day. For general health and gradual weight loss, aim for 150 points a day or about 1,000 points a week. For faster weight loss, reduce dietary calories sharply and aim for 300 CME points a day, or both.

The system encourages people to view physical activities as opportunities, not punishments. Climbing stairs instead of riding the elevator is one example of a healthful choice that incorporates exercise into the fabric of daily life. People should choose whatever activities work for them as long as they add up to enough exercise to maintain good health. And as they experience the personal pleasures of moderate exercise, some will go on to aerobic training or to participate in sports.

People with medical problems or special needs require additional screening and supervision; in particular, everyone with known or suspected heart disease or major risk factors should have a thorough medical check-up and, in most cases, a stress test before starting an exercise program.

Cardiometabolic exercise is the key for health, but many people will get extra benefit by adding exercise for strength, flexibility, or balance — not necessarily at a gym under the watchful eye of a trainer, but at home in just a few minutes a day. And a prudent diet is an essential partner in the prevention of many of the chronic illnesses that plague industrial societies.

Medical science continues to make astounding advances. It has taken the collective effort of many dedicated scientists to bring us back to the wisdom of Hippocrates; some 2,400 years ago, the father of medicine said, "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."