When Jenny Wood-Allen wanted to take part in her first marathon at the age of 71, both her doctor and family were skeptical. But at the age 90, she became the oldest woman ever to complete the grueling 26-mile race, earning her a place in the Guinness Book of World Records.
Now, researchers are finding that senior runners like Wood-Allen may be breaking more than just records.

Following a group of seniors in their 60s and 70s who ran the equivalent of a marathon over the course of each week for several years, a team led by Dr. Bonnie Bruce at Stanford University found that vigorous exercise had a soothing impact on joint and muscle pain, despite the fact that running left them more prone to injuries.

The seniors did more than run: they swam, walked and lifted weights, which left them with significantly less pain compared to those who exercised about half as much. The point, Bruce says, is that just about any type of exercise is helpful, regardless of your age. 

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"The studies on the benefits of physical activity just keep piling up," says Bruce.

The study, published in Arthritis Research & Therapy, followed 492 members of a senior exercise club for 14 years. Most of the gray-haired grandmas and Jack LaLane's clocked just over five hours of regular exercise a week, including 26 miles of running spread out over every seven days.

Bruce's team compared these aging athletes to 374 volunteers who exercised about two hours a week—still respectable considering their age. On average, the participants were just a few years short of retirement when the study began.

Those who continued to run, swim and vigorously walk through their 70's reported suffering about 25 percent less muscle and joint pain than the group who exercised less. This was despite the fact that 53 percent of those who ran 26 miles a week suffered a fracture, versus the 47 percent who injured themselves while running only a couple of miles a week.

Those who gave up running, but still exercised plenty, had about the same benefits. Bruce says that such vigorous exercisers may have a higher threshold of pain to begin with, but by following them for so long, she is confident that improvements were genuine. Indeed, she says that physical activity fits a natural need that many forgot with the invention of the couch.

"Humans were meant to move, not sit," she says. In the very early days, such exercise was geared towards running away from predators and hunting for food. But the same principles apply today.