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
& Exerciseshows 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 inArteriosclerosis, 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 inRockport 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."
