Remember fitness in the 1970s? All those aerobics classes, leotards and sweatbands, the endless jogging and velour track suits? Got to crank up that heart rate to 90 percent of maximum, experts told us. No pain, no gain.
But today a new, easygoing message reigns: Leave the spandex at home - you don't have to sweat or even change your clothes. Simply take a walk. Aim for least 30 minutes of activity on most days of the week, experts advise. Break it up into a few brisk-walking "snacks," if you prefer. Vigorous exercise is great, they say, but don't feel pressured.
What happened? Did experts notice that we weren't living up to their high-heart-rate expectations and decide, with resignation, to lower the bar? Or has the science of exercise evolved into something more subtle than, say, Richard Simmons' shorts?
Yes, and yes.
Public health officials are indeed desperate for us to get off our duffs, and they prefer minimum guidelines that don't scare us off. But research during the past decade has also shown that physical activity doesn't need to be vigorous to be beneficial.
Brisk walking can help prevent cardiovascular disease, colon cancer, osteoporosis and diabetes, researchers say. Those who suffer a broader set of disorders - including breast cancer, depression, cognitive decline and sexual dysfunction - might also benefit from regular strolls around the block.
"Walking may be as close to a magic bullet as you'll find in modern medicine," says Dr. JoAnn Manson, professor of medicine at Harvard Medical School. "If there was a pill that could lower the risk of chronic disease like walking does, people would be clamoring for it."
Walking is the ultimate no-fuss exercise. You don't need training or equipment (though plenty of books and gadgets are available to help). Walking can get you from point A to point B in an earth-friendly, non-gas-guzzling way. It can be fine-tuned to your fitness needs - suitable for just-off-the-couch potatoes and adrenaline junkies alike.
And here's another big plus: Walking is fun, offering up an eye-opening view of a world normally glimpsed only as a car-window blur.
The road to modern exercise science started in the 1950s, when researchers found that London bus drivers who sat behind the wheel all day tended to suffer more heart attacks than their co-workers who walked around the double-deckers punching tickets.
Researchers quickly homed in on a good measurement of physical fitness - the amount of oxygen a body was capable of delivering to muscles during all-out physical exertion. They promoted vigorous exercise as the key to good health.
The first exercise guidelines from the American College of Sports Medicine, released in 1975, encouraged people to exercise vigorously and often, at 70 percent to 90 percent of maximum heart-rate reserve.
(For a rough approximation of the upper range, subtract your age from 220 and multiply by 0.9 - that's about 162 beats per minute for a 40-year-old.)
Ten years later, only 20 percent of Americans met these standards - and 40 percent were still completely sedentary.
Then came a new era in exercise. Evidence was amassing that less-than-punishing exercise had its health benefits, too. In 1995 the American College of Sports Medicine and the Centers for Disease Control and Prevention came up with a brand-new exercise plan: Accumulate at least 30 minutes of moderate physical activity - walking, gardening or golfing, for example - on most days of the week.
The U.S. surgeon general, the National Institutes of Health and the World Health Organization soon followed with similar guidelines.
The new buzz: bite-sized pieces of "physical activity." Brisk walking and similar activities - which gurus once brushed off as too wimpy to do much good - were linked in large, long-term studies to lowered risk for heart disease, diabetes, high blood pressure, colon cancer, osteoporosis, anxiety and depression.
How hard people exercised seemed to be less important than how long they were active. And, it seemed, you didn't even have to do all that exercise at the same time: Intermittent activity was as beneficial as long bouts of exercise.
"It was a bit of a revolution in the world of physical activity," says Steven Blair, professor of exercise science at the University of South Carolina and senior editor for the Surgeon General's report.
Today, even more scientific evidence has stacked up - including some gold-standard randomized clinical trials - showing the benefits of moderate exercise for other disorders, such as Alzheimer's disease, stroke, cognitive decline, breast and prostate cancer and erectile dysfunction.
Some of the conclusions are still surprising, and still debated. Not only is brisk walking better for your health than, say, dozing in front of the TV (no argument there), but apparently it's also nearly as good as spending that time jogging.
"You will get the lion's share of the health benefits of physical activity from moderate-intensity activity, if you do it regularly," says Manson, author of The 30-Minute Fitness Solution: A Four-Step Plan for Women of All Ages. "The greatest boost comes from simply not being sedentary."
In 2001, a Harvard study of 39,000 women published in the Journal of the American Medical Association concluded that as little as one hour of brisk walking a week might cut women's risk of coronary heart disease in half.
The article's subtitle summed up a new attitude in exercise science: "Is 'No Pain, No Gain' Passe?"
Sneaky psychology may also be at play here. "People have an aversion to exercise," says Guy Le Masurier, professor of physical education at Malaspina University in British Columbia. Even the promise of a finish-line euphoria doesn't motivate us very well, he says: "Most people don't get the runner's high because it's just too painful to get there."
Most don't even try. According to national 2005 surveys by the Centers for Disease Control, about 49 percent of Americans get the minimum current recommended moderate activity levels. About 40 percent are completely sedentary during their free time.
"We can give recommendations that would make people very, very healthy, but they just wouldn't do it," says David Bassett Jr., professor of exercise, sport and leisure studies at the University of Tennessee. "If we recommend moderate activity, it's much more palatable, and more people will do it."
In any case, from a public health point of view, nonactive folks are the prize demographic: Get them moving and you'll make a bigger dent in the chronic disease rates than targeting folks who are already somewhat active.
"Where we get our bang for the buck is getting sedentary people from doing nothing to doing a little bit, from off the couch to walking," says James Hill, director of the center for human nutrition at the University of Colorado.
We weren't always so slothful. Eighty years ago, for example, the typical commute to work in Rochester, Minn. (home of the Mayo Clinic), was a 1.6-mile walk. That's about 150 extra calories burned each day - the equivalent of 10 to 20 pounds of body weight each year.
"Humans were designed to walk," says Dr. James Levine, a professor at the Mayo Clinic College of Medicine. "We spent 7 million years of our history walking, and now all of a sudden we're sitting down. We're addicted to our chairs. That is having profound effects on our health."
We balk at adding extra walking into our lives for predictable reasons. In a recent study of undergraduates at the University of California, Irvine, common excuses were lack of time and inconvenient sidewalks. The next most significant cluster of excuses? Not wanting to mess up nice clothes and hair.
But hairdo-friendly walking can be woven into a daily schedule, Levine says. One of his favorite creative suggestions: Transform your daily sit-down meetings with the boss into strolling-around-the-hall meetings.
"Don't change clothes, don't sweat, just carry your clipboard and conduct the same meeting," he says. At a leisurely 1.5 mph, an hour-long meeting can burn 150 calories - about the same benefits that last century's walk-to-workers enjoyed.
Levine himself works from a custom treadmill desk, set for a constant 1 mph. Telephone conversations, reading, computer work: All are performed in the office while enjoying an easy saunter. "It simply takes creativity to see the opportunities to build walking into the day and reap the health benefits," he says.
Burning off pounds is one big way that walking helps a person's health, especially when it comes to warding off diabetes and other diseases for which obesity is a risk factor. But it's not the only way.
Walking enhances blood circulation. It can lower blood pressure and improve blood cholesterol, important for warding off heart disease. It also reduces inflammation and clotting related to stroke.
It enhances the body's handling of glucose (good for diabetes control).
It alters hormone levels (which play a part in breast and prostate cancer).
It boosts bone mineral density (important in osteoporosis prevention).
It enhances the brain's neurotransmitters (good for anything involving mood and creativity).
Some changes happen quickly. Improved cholesterol profiles can show up in as little as two months. And research shows that walking benefits just about everyone - men and women, young and old, fat and thin, and all races, says Dr. I-Min Lee, associate professor of medicine at Harvard Medical School.
Health changes can happen slowly, too. Long-term studies into aging populations have suggested that if you stay active with moderate exercise in your youth and middle age, you're more likely to be healthy, mobile and free from cognitive decline in your golden years.
Even if you're in your 80s and have never been active, by starting to walk you can still enjoy health benefits, says Roger Fielding, director of the nutrition, exercise physiology and sarcopenia laboratory at Tufts University.
In a study published in November, sedentary 70- to 90-year-olds who were deemed to be at risk for disability were assigned to a physical activity program with the goal of walking 30 minutes, five days a week.
After six months, they were able to get out of a chair more easily, balance themselves better and walk faster - all skills that could keep them self-sufficient even longer.
"Many older people are really worried about losing their independence, and we think something as simple as walking exercise may prevent that from happening," Fielding says. "It's never too late."
Regina Nuzzo wrote this article for the Los Angeles Times.