Back in 1963 when I began running as a high-school junior, it seemed a risky business. So many people warned that I would end up a wreck. My heart would grow weak with fatigue. The disks in my back would be ground to dust. My knees, if they moved at all, would creak and groan.

I even detected hints that my brain would turn to mush. “What do you think about when you’re running?” I was asked with clear disdain. “It’s so boring.”

In fact, my running pals and I, all under 30, knew only one runner who had reached the advanced age of 55: “Old John” A. Kelley, two-time winner of the Boston Marathon. I figured the other runners from Kelley’s generation must have died from heart disease. Or were confined to wheelchairs. Or mental wards.

We kept running, but we were spooked. We felt like explorers in a new and perilous land. I remember being particularly concerned about wear-and-tear mechanics. My toothbrush lasted only a month or two, after all, and my father traded in the family car every three years before the engine froze up. Why should runners be any different?

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It took James Fries, a young philosophy student turned Stanford arthritis expert, to offer a radically different perspective. “I’ve always had a knack for looking at old problems from a new angle,” he told me. Fries eventually orchestrated the most compelling exercise science research you’ve probably never heard about. The results are so striking—a potential life-changer and lifesaver—that they need to be understood by every runner. And no less a fitness expert than 86-year-old Ken Cooper—the “father of aerobics”—has spent a lifetime compiling data consistent with Fries’s conclusions. Indeed, almost monthly, research is piling up to bolster the Exercise Is Medicine movement. At this period when almost everyone seems to be turning 65 and thereby threatening to drown our national health-care system, these findings are essential. They are also far-reaching, touching runners of all ages.

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This story begins in 1980, when Fries, a 3:09 marathoner, published a “Special Article” in the prestigious New England Journal of Medicine. In it, he argued that medicine and society must get over their fascination with longevity research. It was more important, Fries wrote, to pursue “compression of morbidity.”

Now, you’ve probably never heard about compression of morbidity (COM), and while it sounds complicated, it couldn’t be simpler. In effect, COM means staying healthy as long as possible so that you decline in old age for as short a time as possible. COM measures quality of life, not just quantity. The ultimate example is an individual who lives a long, active, engaged life for 90 years and then dies peacefully in her sleep.

Fries believed that not smoking, eating healthy foods, and maintaining a healthy weight all contribute to COM. But he theorized that the most important ingredient was consistent exercise. Trouble was, in 1980, he had no evidence to support that theory.

Four years later, he launched his grand experiment the Runners Study. It could hardly have been more elegant. Fries assembled two subject groups that were as similar as possible. Both had more than 400 members who were roughly the same age (59), same weight, same excellent health status, and same education background. Importantly, they all had good health insurance.

The two groups differed in just one significant way: One group, the Runners, averaged 30 to 40 miles a week of running. They came from the Stanford area and also from a national club known as the Fifty-Plus Runners Association. The other group, the community Controls, were mostly members of the Stanford University staff. They did modest amounts of exercise; some even jogged a little as part of a healthy lifestyle. There were few couch potatoes among the Controls.

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Fries first tested the two groups in 1984. Then he sat back and watched his hair grow thinner and grayer. Every seven or eight years, he checked his subjects’ health status again, and wrote an interim report.

In 2008, Fries published a major paper in the American Medical Association’s Archives of Internal Medicine. Titled “Reduced Disability and Mortality among Aging Runners: a 21-Year Longitudinal Study,” the paper summarized his results from 1984 to 2005. The typical surviving subject was then 80 years old. Twenty percent of the Controls had died, but only 15 percent of Runners. On average, the Runners were living seven years longer than the Controls. That wasn’t the big news, however.

Contrary to everything I had been told in 1963, the Runners also had less disability. They weren’t crippled from their lifetime of running. Quite the opposite. It took them 11 to 16 years longer to reach any given disability score on a tool called the Health Assessment Questionnaire—Can you put on your own clothes? Can you cook your own food?—than the Controls. When the Runners’ chronological age hit 80, their quality-of-independent-living age was more like 65 to 70.

This outcome, Fries told me, doesn’t happen overnight. It comes only to those who live healthy and exercise—in this study, that means running—through the decades. “The point here is that aging begins when we are 20 or 30,” Fries says. “You can’t do anything by waiting until you are 70, and then taking Geritol or some other elixir. The runners were benefiting from the cumulative effect of year after year of continuous exercise.”

Let’s repeat those numbers. They deserve the emphasis. On average, the Runners were living seven years longer, and reporting that they felt almost 14 years younger. Wow.

In this regard, the arc toward one’s physical health in old age is exactly analogous to one’s fiscal health. You’re either saving money for retirement, or you’re not. You’re either exercising, or you’re not. You’ll have money in the bank when you get to 65 and beyond. Or you won’t. The decision is yours; the time to act is now.

You probably haven’t heard much from Ken Cooper lately, but he’s still practicing what he has long preached. While a serious skiing injury and subsequent knee surgery a dozen years ago put an end to his running, Cooper is still an avid health walker. Avid as in “fast.” He walks three to four miles most days at a 15-minute-per-mile pace.

Meanwhile, his Cooper Aerobics Center has conducted more than 225,000 maximal stress treadmill tests (without a single fatality) in the last 46 years, using the results to publish more than 600 studies showing that exercise can prolong lives and reduce death from all causes. “We’ve always wanted to show not just that running could be joyful, which has merit, but that we could make it a subject of scientific exploration,” says Cooper.

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In agreement with Fries, the Cooper studies show strong links between fitness and lower mortality rates, as well as decreased risks of heart disease, dementia, and hypertension. For example, a study in a 2013 paper followed more than 19,000 exercisers, mostly runners, through their 50s, 60s, and 70s and found the fittest subjects had a 36 percent lower risk of developing dementia than the least fit.

In 2015, another paper, this one in the American Journal of Preventive Medicine, reported that high-fit Medicare participants used 40 percent less insurance annually than the low-fit. This amounted to a savings of $5,200 per year for men, and $3,900 for women. “In general we have found reductions in many areas of chronic disease,” says Cooper. “When I was in medical school, we were taught that exercise is dangerous. Now we know exercise is medicine and a miracle drug, just as I’ve been saying for 50 years. And the rewards continue for those who keep running past 50 or 60-plus years of life.”

A trio of new papers—some as recent as March 2017—bolster Cooper’s position. One followed 6,100 patients ages 59 to 69 at veterans hospitals. The least fit were 4.42 times as likely to develop dementia or Alzheimer’s as the most fit.

Another examined what might happen if midlife subjects (with an average age of 54) began exercising enough to move from the least-fit group to intermediate or high fitness. The result: They lowered their mortality risk by 40 percent. This proved what geriatrician and lifelong marathoner Walter Bortz, M.D., has often said: “It is never too late to start exercising, but always too soon to stop.”

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Perhaps the most remarkable of the new papers followed 4,000 Spanish subjects from age 60 into their early 70s. By then, many had chronic health problems such as diabetes, heart disease, and high blood pressure. Some with these conditions did little to no exercise. Others kept at their workouts. And boy, did it pay off.

Exercisers with two or more conditions had a 35 and 47 percent lower mortality compared to nonexercisers with the same number of issues. Even more impressive, wrote the researchers, “Physical activity showed beneficial effects in all individuals with any specific chronic conditions.” In other words, exercise improves just about any ailment out there.

For most of his life, James Fries followed his own advice, running at least 500 miles a year. He climbed the highest peak on six continents, and reached Mount Everest’s base camp. Parkinson’s has slowed his activity in recent years, but not his research. He’s updated the Runners Study through another eight years.

The remaining subjects are nearly 90. Since even runners eventually suffer from disability and death, Fries had expected the two groups to converge by now. They have not. The Runners are still living seven years longer while lagging 11 to 16 years behind the Controls in disability stages. “I’m not trying to pander to the Runner’s World community when I say ‘Use it or lose it,’” he told me. “But it’s that simple. Exercise is a self-determined behavior. It’s a health choice we all make. We have control over the outcome.”

That’s good enough for me. Despite all those warnings years ago, I’ve been running for 55 years and have logged about 110,000 miles. My chest feels fine; so do my knees and my back. I ran four times last week, a total of 32 miles, most of them slower than ever. But so what? Every day, exercise is an option, and I choose yes. I’m looking forward to my next run, tomorrow. At 70, it feels good to be looking—and moving—forward.