For those interested in exercising more but worried about their knees, a new study from researchers in the UK this week might offer some reassurance. The research, a review of existing evidence, found no link between exercise and a greater risk of knee osteoarthritis, the most common form of arthritis to plague the joint.
Arthritis is another name for joint inflammation. Osteoarthritis is a degenerative condition in which the cartilage protecting a joint slowly wears down over time, leaving the joint vulnerable to injury and swelling. About 32.5 million Americans have some form of osteoarthritis, though its symptoms vary depending on how far it’s progressed. Those with mild to moderate osteoarthritis may experience some occasional joint pain and stiffness that can be managed with over-the-counter painkillers and home remedies, while those with severe osteoarthritis can experience debilitating pain and disability that can only be helped with surgeries like a knee replacement.
Age is the largest risk factor for osteoarthritis, along with others like sex (women report it more often), genetics, and weight, since it can put more stress on the knees. Physically stressful jobs that require lots of heavy lifting and knee-bending have been linked to osteoarthritis as well. It’s less clear whether physical activity outside of work can cause or worsen knee osteoarthritis, though it’s certainly a common fear that exercises like running will eventually ruin your knees.
The authors of this new paper, published Wednesday in Arthritis & Rheumatology, looked at data from six earlier studies tracking a combined 5,065 participants over the age of 45 for about five to 12 years, all of whom did not have diagnosed knee osteoarthritis at the start of the study. This kind of research is known as a meta-analysis, but the authors went one step further than most studies do, by first collecting the raw patient data from each study and then re-analyzing it all at once. These “individual patient-level data” meta-analyses are more time-consuming and expensive to conduct but are generally considered more reliable as a result, since they can better account for the many differences across studies.
Ultimately, the authors found no significant link between the risk of developing knee osteoarthritis and either the amount of exercise done regularly or the time spent exercising.
“Knowing that the amount of physical activity and time spent doing it is not associated with the development of knee osteoarthritis is important evidence for both clinicians and the public who may need to consider this when prescribing physical activity for health,” said co-lead author Thomas Perry, a researcher with the University of Oxford in the UK, in a statement from Wiley, the publishers of the journal.
Other research has cast doubt on the idea that specific types of exercise, particularly running, will inevitably doom your knees, and regular runners may have a smaller risk than average (that’s not to say that some forms of knee pain aren’t more common for them). For those who already have osteoarthritis, stretching and strengthening exercises can even help relieve symptoms, and too much inactivity can do more harm than good by causing stiffness.
The studies do rely on self-reported exercise levels, so they are subject to some bias. And the researchers weren’t able to look at the impact of individual exercises on the knee. So it’s possible there may be a link between specific forms of exercise and knee osteoarthritis, either good or bad, or with exercise among people who are already susceptible to knee problems because of preexisting injuries. The authors say that more research is needed to tease out these interactions—ideally by relying on objective measurements of physical activity.