If you're a runner, you might have noticed this surprising headline from the April 5 edition of the Guardian: "Brisk walk healthier than running—scientists." Or maybe you saw this one, which ran in Health magazine the very same day: "Want to lose weight? Then run, don't walk: Study."
Dueling research from rival academic camps? Not exactly. Both articles described the work of a herpetologist-turned-statistician at the Lawrence Berkeley National Laboratory named Paul T. Williams, who, this month, achieved a feat that's exceedingly rare in mainstream science: He used exactly the same dataset to publish two opposing findings.
One of Williams' papers, from the April issue of Medicine & Science in Sports & Exercise shows that habitual runners gain less weight than habitual walkers, when the amount of energy they put into their exercise routines is the same. The other, published in April in Arteriosclerosis, Thrombosis, and Vascular Biology, used a similar analysis to show that running is no better than walking when it comes to the prevention of high blood pressure, high cholesterol, diabetes, and coronary heart disease. So there you have it, and there you don't. Running is better for your health, or perhaps it isn't.
Despite the flip-flop headlines, the findings are not as contradictory as they seem. Losing weight is not the same thing as getting fit—your metabolic health has more to with triglycerides and hypertension than it does with your size in chinos—so there's no fundamental reason why Williams' walkers couldn't gain more weight than the runners while their risk for cardiovascular disease remained the same. The 47,000 people involved in Williams' study were drawn in large part from middle-aged subscribers to exercise magazines who agreed to fill out his surveys, and most of them were slender at the outset. They started with an average BMI in the “normal” range, between 21 and 25. (Overall, middle-aged, U.S. adults have an average BMI of more than 28.) Since the health risks associated with being fat don't kick in until you're very large, they wouldn't necessarily apply to Williams' subjects.
But the deeper story here has more to do with Williams' second finding, that neither form of exercise was any better than the other at promoting cardiovascular health. When Williams set up his gigantic database of avid runners and walkers in the early 1990s, he hoped to help resolve an old debate in exercise science: If you match up workouts according to the amount of energy that they require, are all forms of physical activity created equal? Would a tough and sweaty workout be any better for your health than an easygoing one that lasted twice as long?
Researchers began to ask these questions in the early 1980s, in response to worries over the health effects of jogging. In two decades, the number of self-identified runners in the nation had grown from 100,000 to 30 million, but as the fitness craze expanded, so did concerns about its downsides. Doctors started talking about the natural "endorphin high," and worried that a person might become addicted to certain forms of physical activity. The incidence of shin splints seemed to be increasing, too, along with heel spurs, stress fractures, and inflammations of the knee. Could all this compulsive running be doing more harm than good?
Those fears were realized in the summer of 1984, when the 52-year-old best-selling author and running guru Jim Fixx collapsed dead in his jogging shorts, having had a massive heart attack just 100 yards down the road from his motel. At around the same time, the president of the Rockport shoe company paid a cardiologist named James Rippe to investigate the benefits of walking. Might a less intense form of exercise do the body good? Rippe, who would later write Heart Disease for Dummies and found the Rippe Lifestyle Institute in Orlando, Fla., released some promising data. If you take a swift, half-hour stroll at least three times per week, he said, that should be enough to improve your cardiovascular fitness by 15 percent.
Now the sporting goods industry had a bit of science to support a new and (allegedly) safer form of exercise. By this point, enthusiasm for running was already in sharp decline—the number of joggers in the United States would fall by almost 40 percent between 1979 and 1985—and Rockport led the charge to invent the leisure-time pursuit of "power walking." In the fall of 1984, just a few months after Jim Fixx's death cast a shadow over recreational running, Rockport started selling the ProWalker athletic shoe, the first product in its class.
The trend for walking reached its stride in 1986, with nearly 20 million participants and the inaugural issue of Walking magazine (tagline: "Stop Talking, Start Walking"). This was big business, too: More than 40 companies followed Rockport's lead and released versions of the walking shoe. "If you look at the fitness boom as ripples on a pond, then jogging was the first ring, aerobics the second, and we think walking is the third," said the advertising director for Nike to the Los Angeles Times in 1987.
But mainstream researchers in the field of exercise were a little slower to buy in. Government standards for physical activity, based on advice from the American College of Sports Medicine, still favored more vigorous activities such as running. It prescribed at least half an hour of heavy exercise at least three times per week. "I wrote the guidelines, and I still hold to them," said Michael Pollock, a prominent exercise physiologist, in the middle of the walking hype. The debate in academia would last for almost a decade.
Finally, in the mid-1990s, government agencies softened up in deference to the power walkers. Now Americans were advised to do at least half an hour of something less intense than running—a brisk 4- or 5-mph promenade, for example—but they were advised to do this lighter work more often. In other words, their total dose of exercise would be the same, but they would be taking it in a less concentrated form.
The present version of the guidelines makes this logic more explicit. The Centers for Disease Control and Prevention equalizes workouts of varying intensities according to a standard exchange rate of 2-to-1: Every two minutes we spend hoofing around in Rockport ProWalkers equates to a single minute spent on the jogging trail. That means people can mix and match their workouts until they approximate a recommended weekly total: Either 75 minutes' worth of sweaty, vigorous workouts, or a double helping (150 minutes) of something moderate—or any custom combination of the two.
Williams calls this the "exchangeability premise," that any form of exercise can be subbed in for any other, and that their effects on health will be identical once corrected for the amount of energy that goes into them. Obesity experts often talk about the same idea, using the phrase "calories-in/calories-out." Either way, they're subscribing to a model of personal health where quantity trumps quality. It doesn't really matter what we choose to eat—fats or carbs or proteins—or which machines we end up using at the gym. All that counts is the total energy we absorb from food, minus the total energy we expend in action.
Several of Williams' recent findings support this notion. Most recently, he found that running and walking have about the same effect on risk for high blood pressure, high cholesterol and diabetes as long as they're matched up for total energy expenditure. (That is to say, someone who walks for two hours a day will see the same benefit as a matched control who runs for half that time.) In two other papers from the past few months, he showed that running and walking produce equivalent reductions in the risk of osteoarthritis, hip replacement, and cataracts.
An Australian research group has just released a study confirming this idea. For that paper, published March 28, the scientists followed about 11,000 middle-aged women over a 12-year stretch and compared both their total exercise and types of exercise to signs of hypertension and depression. They found that, in general, women who never bothered with vigorous activity were at no greater risk than the others, even when they were matched for total levels of exertion.
Yet Williams' papers and the Australian one suffer from a common flaw: With this type of research, it's impossible to know what hidden factors might be biasing the data. In Williams' group, for example, the runners could have been eating less overall, or they could have been more inclined to exaggerate their workouts. The sorts of long-term, case-controlled studies that could prove the exchangeability premise once and for all would be almost impossible to carry out.
So it's possible that running and walking aren't quite the same, after all. The calories-in/calories-out model does have some notable detractors. The endocrinologist Robert Lustig and journalist Gary Taubes have made a case for saying that food quality does matter, and some calories are worse than others. Could the same critique be applied to exercise? Might some forms of exercise be like eating fruits and vegetables, while others are like eating meat and dairy?
Williams notes that runners do seem to get some extra benefit from their exercise. In short-term studies, he says, they show improvement at making up for bouts of overeating. (If they get a big meal at one sitting, they'll eat less at the next.) They also experience a heightened metabolism that extends beyond the period of working out.
But runners have another, more important edge: They get more done in less time. A vigorous workout is quicker to finish, so it fits more easily into a busy schedule. That may be why the runners in Williams' cohort ended up getting more exercise, over all.
With that in mind, I asked Williams—a runner himself—if he'd recommend the more vigorous activity. He declined to answer. "I'm not really an exercise advocate," he said. "I don't really care if people exercise or not. But I do care about good science."