It's even more common for people with joint disease to be couch potatoes than previously thought.
Researchers from Northwestern University found that more than half of women and 40 percent of men with knee osteoarthritis are not taking part in exercise.
They measured the physical activity of more than 1,000 people with knee osteoarthritis for a week. Even though federal guidelines recommend adults with arthritis work out for 20 minutes every day, the study found fewer than one in seven men and only one in 12 women met those guidelines.
The findings are published in the August issue of Arthritis and Rheumatism.