Intense treadmill exercise can be safe for people who have recently been given diagnoses of Parkinson’s disease and may substantially slow the progression of their condition, according to an important new study of adults in the early stages of the disease.

But the same study’s results also indicate that gentler exercise, while safe for people with Parkinson’s, does not seem to delay the disease’s advance.

As most of us know, Parkinson’s disease is a progressive neurological disorder that involves problems with motor control. Symptoms like weakness, stiffness, loss of balance and falls can make exercise difficult and potentially hazardous. Though Parkinson’s is currently incurable, its symptoms can be eased for a time with various drugs.

But most of those drugs lose their effectiveness in people over time.

So some researchers have begun searching for other treatment options, particularly for use in the beginning stages of the disease. If people with early Parkinson’s could brake the disease’s advance and delay their need to start medications, the researchers have reasoned, they might change the arc of their disease, delaying its most severe effects.

That possibility recently led a consortium of researchers from Northwestern University, the University of Colorado’s Anschutz Medical Campus in Aurora and other institutions to look at exercise as a treatment.

There were precedents. Animal studies already had shown that exercise reduced symptoms and slowed physical decline in a rodent version of Parkinson’s. But rodents are not people.

And while some previous studies in people have shown that cycling (especially on a tandem bike), boxing, dancing and other activities may produce benefits in people with Parkinson’s, other studies had produced inconsistent results. In addition, many of these earlier studies had used many different types and amounts of exercise, and none had systematically compared different varieties of exercise head-to-head.

So for the new study, which was published in JAMA Neurology, the researchers decided to treat exercise as if it were a drug and carefully track the safety and effectiveness of different “doses” of exercise in a formal Phase 2 clinical trial.

In drug research, Phase 1 trials establish the basic safety of a drug in small-scale experiments. Phase 2 studies look at larger groups of people to see if the intervention remains safe and also whether, in the tortured English of pharmacopoeia, it is “nonfutile,” meaning that it has enough beneficial effect to deserve further testing.

For this Phase 2 study, the researchers first recruited 128 men and women who had been diagnosed with Parkinson’s within the past five years. None yet were taking medications to treat the disease. None regularly exercised.

The researchers tested their aerobic capacity, maximum heart rates and disease severity, using a standard numerical scale. They then divided the men and women randomly into three groups, one of which was asked to continue their normal lives as a control. (For fairness, they were wait-listed for exercise training later.)

The others were assigned to start exercising.

One group walked gently for 30 minutes on a treadmill four times a week, while the researchers manipulated the machines’ speed and incline to keep each volunteer’s heart rate at between 60% and 65% of his or her maximum.

The others exercised for the same amount of time, but at a strenuous pace and incline, so that their heart rates stayed at between 80% and 85% of their maximum.

For a month, the sessions were supervised. Then the volunteers were asked to continue on their own, with heart rate monitors substantiating their efforts.

The researchers asked to be told about any injuries among the volunteers.

Then, at the end of six months, they rechecked the volunteers’ disease status.

To no one’s surprise, the men and women who had continued with their previous lives showed some worsening. Their scores on the disease scale had declined on average by more than three points.

Likewise those in the moderate exercise group showed declines of around two points, meaning that, by the study’s standards, the exercise had been “futile” as a Parkinson’s treatment.

But the group that had worked out intensely showed almost no decline in their disease scores, meaning their exercise had been “nonfutile.” It had helped.

Just as important, it had been tolerable. Almost everyone in both exercise groups had managed to complete six months of regular exercise without injuries and with only sporadic complaints of sore muscles.

The study was not designed to determine why intense exercise slowed the progression of Parkinson’s and moderate exercise did not.

But “my guess is that high-intensity exercise does a better job at improving brain vascularity and neuronal blood supply,” says Daniel Corcos, a professor of human movement sciences at Northwestern University Feinberg School of Medicine who helped to lead the study.

Improved blood flow to the brain, the thinking goes, may aid overall brain health and slow deterioration. But that hypothesis will need to be tested, he says.

A larger, longer-term Phase 3 study of intense exercise as a treatment for early Parkinson’s also is needed, he says, and is now justified, based on these results. He and his colleagues are in fact already planning such an experiment.

But in the meantime, the results indicate that someone who has recently received a diagnosis of Parkinson’s might consider “an intense exercise program,” he says.

Speak with your doctor first, naturally, and perhaps consult an athletic trainer familiar with Parkinson’s. But the findings are encouraging, suggesting that intense exercise is unlikely to be harmful and, in meaningful ways, could help.

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