Evidence that Swimming May Be Protective of Knee Osteoarthritis: Data from the Osteoarthritis Initiative

Background: To date, there have not been any epidemiologic studies that have evaluated the association between swimming over a lifetime and knee health. Objective: The study aimed to evaluate the relationship of a history of swimming with knee pain, radiographic knee OA (ROA), and symptomatic knee OA (SOA). Design: Cross-sectional retrospective study. Setting: Four academic centers in the United States. Participants: Respondents to the historical physical activity survey within the Osteoarthritis Initiative with knee radiographs and symptom assessments. Methods: In this retrospective study nested within the Osteoarthritis Initiative, researchers performed logistic regression with the predictor being swimming over a lifetime and over particular age ranges. Main Outcome Measurements: Person-based definitions of frequent knee pain, ROA, and SOA. Results: A total of 2637 participants were included, with a mean age of 64.3 years (SD 8.9), body mass index of 28.4 kg/m² (SD 4.9), and 44.2% male. Over a lifetime, the adjusted prevalence measures for frequent knee pain, ROA, and SOA for any versus no history of swimming were 36.4% (33.4% - 39.5%) v. 39.9% (37.4% - 42.5%), 54.3% (51.0% - 57.6%) v. 61.1% (58.4% - 63.7%), and 21.9% (19.4% - 24.7%) v. 27.0% (24.7% - 29.4%) respectively. Conclusions: This is the first epidemiologic study to indicate that swimming is potentially beneficial toward knee health, particularly when performed earlier in life (before age 35). Future prospective studies are needed to confirm these findings and to better scrutinize the associations in older age groups.