Walking 6,000 steps per day reduced the risk of functional limitations in people with knee osteoarthritis (OA), according to a new study published recently online in Arthritis Care & Research. Functional limitations are the kinds of mobility problems that affect day-to-day life, such as trouble getting out of a chair or bed, climbing stairs or even walking down the street.

Exercise in general is known to be beneficial for people with OA, and walking, specifically, has long been recognized as being among the best type of exercise. Among its many benefits, walking has been shown to reduce pain, increase flexibility and strengthen the muscles around the joints. It also increases blood flow in and around the joints, and it helps nutrients circulate into knee cartilage.

But many people with arthritis don’t walk enough. According to a report published in May 2013 by the Centers for Disease Control and Prevention, two-thirds of U.S. adults with arthritis report walking (for exercise) less than 90 minutes per week.

But what about “unstructured” walking – the steps people accumulate in the course of an average day? Does that help people become physically active enough to avoid functional limitations and live normal, active lives? And if so, how much unstructured walking is enough? That’s what the researchers wanted this new study to resolve.

“We have numbers in our society for cholesterol, blood pressure, weight – all these numbers we’re supposed to target. But for physical activity, it’s a little unclear,” says lead study author Daniel K. White, a physical therapist and research assistant professor at Boston University’s College of Health and Rehabilitation Sciences. “Anecdotally, 10,000 steps a day is a number floating around, but for someone with painful knee OA, that could be quite a daunting task.”

For their research, White and his team examined data from a previous study, called the Multicenter Osteoarthritis Study. That study involved a large number of people who had knee OA or were at high risk for it. At one point, the participants were given an activity monitor to wear for one week so the researchers could track how much they moved.

White and colleagues focused on almost 1,800 participants who started out with no functional limitations and noted how much each walked. Two years after their activity level was measured, the researchers looked at how well the participants were doing. It turns out that between 4 percent and 8 percent had developed functional limitations. Those who walked more were less likely to be in that group, and the “magic number” of daily steps that divided the two groups was 6,000. Taking even more steps yielded additional benefits.