Not only does running as a routine exercise in life not increase the risk of developing knee osteoarthritis, it may even help prevent developing this painful disease, according to new research presented this week at the annual American University Rheumatology Conference in Boston. Osteoarthritis, or OA, is the most common joint disease that afflicts middle-aged and older adults. It is characterized by progressive damage to the articular cartilage (the cushioning tissue at the end of the long bones) and changes in the structures surrounding the joint. These changes may include fluid accumulation, bone loss, and muscle and tendon laxity and atrophy, all of which may lead to limited motion, pain, and swelling. Knee osteoarthritis is a common form of OA and is caused by the destruction of cartilage in the knee. Factors that may increase the risk of knee osteoarthritis include: obesity, age, joint stress or injury, and family history. Past studies on the possible link between running and knee osteoarthritis have focused on elite male runners, so those results may not apply to the general population, the study’s authors mentioned. The consideration that regular running may lead to knee osteoarthritis is based on the fact that chronic, mechanical knee overload may (cause) damage. However, runners typically have a low body mass index, or BMI-a protective factor against knee osteoarthritis. “Recent CDC guidelines recommend that all adults participate in regular physical activity because there is clear evidence (that) increased physical activity is associated with decreased cardiovascular events and mortality,” said study first author Grace Hsiao-Wei Lo (MD, MSc, Baylor University School of Medicine). “However, the effect of these physical activities on knee osteoarthritis is unclear. Because running is a common amateur physical activity that involves repetitive loading and can be harmful to the joints, I was interested in examining how unusual running might be associated with the development of knee osteoarthritis.” To find out if unusual running increases the risk of osteoarthritis in the general population, the researchers applied data from a multicenter observational study, the Osteoarthritis Initiative (OAI). Of the 2,683 subjects, 56 percent were women, with a mean age of 64.5 years and a mean BMI of 28.6. 29 percent of the subjects reported that they ran at some time in their lives. Patients who had a knee radiograph were evaluated for symptoms and asked to complete the Lifetime Physical Activity Questionnaire (LPAQ) to identify the 3 most frequent physical activities (≥10) they did at different ages during their lifetime. Age groups included 12-18 years, 19-34 years, 35-49 years, and 50 years and older. At 48 months of OAI follow-up, radiographic evidence of osteoarthritis was scored using the Kellgren-Lawrence (KL) grading scale after knee radiographs were done. subjects with KL scores greater than 2 or higher were considered to have radiographic manifestations of knee osteoarthritis (ROA). The investigators also tested subjects for frequent knee pain during their 48-month follow-up. Subjects were considered to have symptomatic knee osteoarthritis (SOA) if they had frequent pain in at least one knee with ROA. Anyone with a total knee replacement was classified as having frequent knee pain, ROA, and SOA. after collecting all the data, the researchers reported that runners (regardless of their age at running) had a lower prevalence of knee pain, ROA, and SOA than non-runners. For those who ran at any time in their lives, 22.8% had SOA compared to 29.9% of non-runners. those with the lowest BMI scores were most likely to report being habitual runners. The researchers concluded that regular running, even when not at the level of an athlete, not only does not increase the risk of knee osteoarthritis, but may be a protective factor against it. “This does not address the question of whether running is harmful to people in a pre-knee osteoarthritic state,” said Dr. Lo. “However, in people who do not have knee osteoarthritis, there is no reason to restrict participation in regular running at any time of life in the sense that running has not been shown to be harmful to the knee. “Funding sources for the study included the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) of the National Institutes of Health, the Center for Innovation in Quality, Effectiveness and Safety and the Michael E. DeBakey VA Medical Center in Houston.