The workouts we completed years ago may continue to influence and improve our health today, according to a fascinating new study of the current lives and health of people who joined an exercise study a decade before.
The findings suggest that the benefits of exercise can be more persistent than many of us might expect, even if people are not exercising to the same extent as they previously did. But the impacts also may depend on the types and amounts of exercise involved.
In medicine, lingering health consequences from experiments, known as legacy effects, are common and often commendable. Participants in past diabetes experiments, for instance, whose blood sugar was tightly controlled with diet, drugs or other methods, often had better heart health years later than diabetics outside of the study, even though the volunteers’ blood-sugar levels had risen in the interim.
But whether exercise studies likewise produce legacy effects has been unknown, although the issue matters. We know from other science and disheartening personal experience that we lose much of our fitness and associated health benefits if we stop or reduce how much we exercise over the years.
But do all of those gains disappear, or might exercise change us in some ways that stick with us?
For the new study, which was published this week in Frontiers in Physiology, scientists at Duke University decided to find out. Most of the researchers had been involved a decade earlier in a large-scale exercise experiment called Strride (for Studies Targeting Risk Reduction Interventions through Defined Exercise).
In that experiment, which ran from 1998 to 2003, hundreds of sedentary, overweight volunteers between the ages of 40 and 60 had remained inactive as a control group or begun exercising.
Their exercise was either moderate, such as walking, or more vigorous, comparable to jogging, and lasted until people had burned at least several hundred calories per workout. Volunteers completed three session of their assigned workout each week for eight months, while scientists tracked changes to their aerobic fitness, blood pressure, insulin sensitivity and waist circumference.
In general, each of those health markers improved in the people who exercised and not in the controls.
The scientists then said farewell and did not get in touch with the participants again until about a decade later, when they contacted volunteers who still lived near Duke and asked if they would join a reunion study. More than a hundred, representing each of the exercise and control groups, said, sure.
These men and women returned to the lab for new tests of their aerobic fitness and metabolic health. They also completed questionnaires about their current medical condition and medications and how often they exercised each week.
Then the researchers started comparing results and found telling differences.
Most of the men and women from the control group, who had not exercised 10 years before, had larger waistlines now, while the exercisers displayed little if any middle-aged spread compared to their decade-earlier selves.
Those from the control group also were less fit now. Most had lost about 10 percent of their aerobic capacity, which is typical of the declines seen after about age 40, when most of us will lose about 1 percent of our fitness annually.
But those men and women who had exercised vigorously for eight months during Strride retained substantially more fitness. On average, their aerobic capacity had fallen by only about 5 percent, compared to when they had joined the Strride study, and those few who reported still exercising at least four times a week were more fit now than they had been a decade before.
Interestingly, those Strride volunteers who had walked — meaning their exercise had been moderate, not intense — did not seem to have enjoyed the same lasting fitness benefits as those who had exercised more vigorously. Most of them had shed about 10 percent of their aerobic capacity during the past decade, much like the controls.
On the other hand, they showed surprisingly persistent improvements in their metabolic health, more so than among the intense exercisers. The walkers from 10 years ago still had healthier blood pressures and insulin sensitivity than they had had before joining Strride, even if they rarely exercised now. They had also had relatively healthier metabolisms than the men and women who had exercised intensely all those years before.
Taken as a whole, these results suggest that “exercise is a powerful modulator of health, and some effects can be quite enduring,” says William Kraus, a professor of medicine and cardiology at Duke, who oversaw the new study.
But the effects also can differ, depending on how hard someone works out, he says. To build and maintain high endurance, we may have to sweat and strain. But to better our metabolic health, a walk likely will do.
Of course, this study does not explain how exercise alters our body in ways that last. We may, in part, be building a physiological reserve, Dr. Kraus says. Raise aerobic capacity or improve insulin sensitivity with exercise, and even as those measures decline later with inactivity and age, we will be better off than if we had never worked out.
Exercise also probably leaves long-lasting imprints on our genes and cells that affect health, Dr. Kraus says.
He and his colleagues hope to investigate those issues in coming studies, so that we can better appreciate how past exercise might echo through our bodies well into the future.