A new study outlines ways to reduce or even eliminate your risk of developing knee arthritis.

You probably know someone who's had a knee replacement. It's a common procedure, with around 790,000 surgeries performed each year in the U.S.

Osteoarthritis is the leading cause for most knee replacements, often leading to pain, swelling, and reduced mobility. This condition is linked to high rates of disability and morbidity, according to a study published in August 2023 in the journal *Experimental and Therapeutic Medicine*.

Those at greatest risk for knee osteoarthritis include older adults, women, people who are overweight, and athletes in sports like soccer, tennis, and long-distance running. Genetics and past knee injuries also contribute to the risk.

Recent research, published in April in *JAMA Network Open*, suggests that strengthening your leg muscles could help slow or even prevent the onset of knee osteoarthritis.

‘Muscle mass is crucial’

In a meta-analysis of data from 5,003 patients in the Netherlands, researchers found no correlation between overall physical activity and an increased risk of knee osteoarthritis. The patients were then divided into two groups: one engaging in non-weight-bearing activities like swimming and cycling, and the other participating in weight-bearing activities such as walking and running.

The researchers identified that individuals who participated in weight-bearing activities were more likely to develop knee osteoarthritis if they had low muscle mass in their lower limbs.

“After observing that only weight-bearing activities posed a risk for knee osteoarthritis, we investigated whether the amount of muscle around the joint played a role,” explained Dr. Joyce van Meurs, study coauthor and professor of population genomics in musculoskeletal diseases at Erasmus Medical Center in Rotterdam, Netherlands.

Since larger muscle mass can help protect and cushion the knee from internal mechanical forces, the researchers hypothesized that individuals with stronger muscles would have a better outcome compared to those with weaker muscles.

“And that’s exactly what we observed,” said van Meurs. “When individuals had greater muscle mass, the increased risk of developing osteoarthritis from weight-bearing sports was not evident.”

This discovery is an exciting development, commented Dr. Kathryn Miller, an associate professor at the University of Wisconsin School of Medicine and Public Health in Madison.

“We’ve always believed that muscle mass plays a key role in protecting joints,” said Miller, who was not involved in the study. “Now, this study begins to confirm that muscle mass is essential for joint function and may also reduce the risk of osteoarthritis.”

Implications of this study for exercise and sports

While the study’s results are significant, there is still much more to explore, according to van Meurs. For instance, weight is known to be the largest risk factor for developing knee osteoarthritis. The data van Meurs and her team analyzed came from individuals with an average body mass index (BMI) of 26. (BMI is a measurement of body fat based on height and weight.)

A BMI of 26 is slightly above the healthy range but still lower than the average BMI for people in the U.S. Could the study's conclusions be applied to those who are overweight or obese?

“We’re not entirely certain,” said van Meurs. “BMI is a significant risk factor for knee osteoarthritis. If it plays such a dominant role, perhaps the relationship with other factors isn’t the same.”

Miller shared the same view: “The higher your BMI, the more strain you're putting on your joints, especially during weight-bearing activities,” she explained. “People with higher BMIs may need even stronger lower-limb muscles than those with lower BMIs.”

A new large-scale study at Erasmus Medical Center is exploring whether doctors can tailor their recommendations for patients based on factors such as muscle mass, weight, and joint mobility.

“We’re examining how much stress individuals can safely put on their joints, taking these factors into account,” said van Meurs. Many patients with knee pain ask their doctors if it’s safe to keep doing their favorite activities, but there’s no clear answer at the moment.

How to exercise safely

Despite these unanswered questions, the study provides several important insights.

“Before engaging in high-impact activities, make sure to train your leg muscles in the gym,” advised van Meurs. “And if you plan to take up a weight-bearing exercise like running, ease into it gradually.”

“It's not just your muscles that need to adapt to these new stresses, but your tendons too. Otherwise, you risk injury right away,” she explained.

Miller advises her patients to maintain a healthy weight and stay active. “And if you're diagnosed with osteoarthritis, don’t quit your activities,” she said. “People who are inactive tend to have poorer joint health and muscle mass, putting them at higher risk of developing symptomatic osteoarthritis.”

So take a walk, try some wall sits, or sit in a chair and stand up 10 times without using your arms to push yourself up, suggested Miller. The key is to keep moving.

“For osteoarthritis patients, our guideline is that mild discomfort during activity is okay as long as it fades quickly,” said Miller. “However, if the pain increases and doesn’t improve the next day, the activity might be too strenuous for your joint at the moment.”