It’s long been known that many arthritis patients tend to be sedentary, but a report shows just how pervasive the problem is. The study, published in Arthritis & Rheumatism, found that fewer than 1 in 7 men and 1 in 12 women with knee osteoarthritis, or OA, were physically active enough to meet federal guidelines. The U.S. Department of Health and Human Services recommends 150 minutes of moderate-intensity, low-impact activity per week.

In fact, 57 percent of women and 40 percent of men were classified as “inactive” – that is, they did not engage in moderate-to-vigorous activity for 10 minutes or more at any time during the course of a week.

This level of inactivity is higher than that found in earlier studies, mainly because previous studies relied on self-reporting as opposed to objective measurements.

“I think everyone knew people with arthritis were not particularly active. This proves that … it’s a major, major issue,” says study co-author Rowland W. Chang, MD, MPH, a professor of preventive medicine and rheumatology at Northwestern University’s Feinberg School of Medicine in Chicago. “The lack of physical activity is the major health issue for persons with arthritis to confront.”

Using a machine called an accelerometer to register all motion during waking hours, the researchers measured the activity of 1,111 knee OA patients between the ages of 49 and 84. Although this study didn’t compare self-reported physical activity levels with actual accelerometer data, Dr. Chang notes that most people overestimated their activity level by at least two-fold.

Dr. Chang says the study defined “moderate intensity” as activity that raises your heart rate, making you a little sweaty but still allowing you to carry on a conversation.

Physical activity is very important for people with OA: It has been shown to help reduce pain and symptoms of depression, fight fatigue, increase function and physical performance, and prevent or delay disability in knee OA, as well as improve general health and reduce the risk of several chronic diseases. An earlier study by some of the same researchers found that OA patients benefit from some physical activity even if they don’t reach the recommended 150 minutes per week, and the more they exercise, the greater the potential benefit.