Physical activity is associated with MR-based knee cartilage T2 measurements in asymptomatic subjects with and without osteoarthritis risk factors. Hovis KK, Stehling C, Souza RB, Haughom BD, Baum T, Nevitt M, McCulloch C, Lynch JA, Link TM. Arthritis Rheum. 2011 May 2. doi: 10.1002/art.30419. [Epub ahead of print] In February, SMR posted a systematic review that indicated that while physical activity was associated with osteophytes (bone spurs) there was no relationship between physical activity and joint space narrowing (and may be related to having less cartilage defects). We noted in that post that more research was needed to evaluate various types/amounts of physical activity among different patient populations. To further answer these questions, Hovis et al. evaluated the cross-sectional association of exercise and knee-bending activities with magnetic resonance (MR)-based measures of knee cartilage in 128 asymptomatic participants with risk factors (e.g., history of injury/surgery) for symptomatic knee osteoarthritis (OA) and 33 participants with no OA risk factors. The authors used the Osteoarthritis Initiative, a large NIH-funded, multicenter, longitudinal epidemiology study that offers publicly available data and medical images (e.g., MR imaging, x-rays). A physical activity questionnaire was used to stratify participants into three categories: 1) moderate-strenuous exercises who performed frequent higher impact exercise (e.g., running), 2) light exercises who performed frequent lower impact exercise (e.g., walking), and 3) sedentary participants (they excluded participants that did not clearly match these definitions). Frequent (most days in past month) knee bending activities (e.g., climbing up 10 or more flights of stairs/day, kneeling for more than 30 minutes/day) were defined on a separate question. MR images were evaluated for two types of cartilage measurements: 1) quantified T2 relaxation time mapping; which can detect early-degenerative changes in cartilage composition (changes in water or altered architecture), and 2) cartilage abnormalities scores. Among participants at risk for symptomatic knee OA, light exercisers had better cartilage structure (lower T2 measurements meaning less water content and more intact architecture) than participants who were sedentary or performing frequent moderate-strenuous exercise. In both groups (with and without risk factors) frequent-knee bending activities were associated with cartilage degeneration (higher T2 measurements and more severe cartilage lesions). The authors conclude that among individuals with risk factors for knee OA light exercise (e.g., frequently walking) may aid in preventing early-cartilage degeneration. Furthermore, individuals that perform frequent knee bending activities have greater cartilage degeneration than those who don’t frequently perform those activities. While this study does not answer the question about the influence of different types of physical activity performed earlier in life among patients at risk for OA it does provide important insights about how we can advise our patients/athletes who are concerned about developing OA after a joint injury. Low-impact exercises may be a valuable intervention that athletes with a history of knee injury/surgery can incorporate into their daily activities, as they age, to reduce their risk of developing OA; but this will need to be further verified in studies that follow patients over time and in clinical trials. Whether or not moderate-strenuous exercises influences cartilage health may need to be further explored with more participants but large longitudinal epidemiology studies, like the Osteoarthritis Initiative, may help us gain a better understanding of the influence of physical activity on joint degeneration among participants with OA or participants with or without risk factors for knee OA. Written by: Jeffrey DribanReviewed by: Stephen Thomas