Transform your leisure time into a productive workout session while you catch up on your favorite shows. Consult your healthcare provider before starting any new fitness regimen and discontinue immediately if you experience discomfort or pain.

It's likely that you're acquainted with someone who has undergone a total knee replacement. This procedure is quite prevalent, with approximately 790,000 surgeries performed each year in the United States. The majority of these surgeries are due to osteoarthritis in the knee, which can result in pain, swelling, and reduced mobility. A study published in the journal Experimental and Therapeutic Medicine in August 2023 identified knee osteoarthritis as a condition with a significant impact on morbidity and disability. The demographic most susceptible to this condition includes older individuals, women, those with excess weight, and participants in sports such as soccer, tennis, and long-distance running. Genetic predisposition and past knee injuries are also contributing factors.

However, recent research has indicated that it may be possible to mitigate the progression of knee osteoarthritis or even prevent its onset by bolstering the strength of your leg muscles. This was revealed in a study published in JAMA Network Open in April. The study involved a meta-analysis of data from 5,003 patients in the Netherlands, which found no correlation between an individual's overall physical activity and the risk of developing knee osteoarthritis.

The researchers categorized the patients into two groups: those who engaged in non-weight-bearing activities like swimming and cycling, and those who participated in weight-bearing sports such as walking and running. The findings indicated that individuals who partook in weight-bearing recreational physical activities were at a higher risk of developing knee osteoarthritis if they had low levels of lower-limb muscle mass.

Dr. Joyce van Meurs, a co-author of the study and a professor specializing in population genomics in musculoskeletal diseases at Erasmus Medical Center in Rotterdam, Netherlands, explained, "After noticing that only weight-bearing sports increased the risk of knee osteoarthritis, we investigated whether the development of the condition was contingent upon the amount of muscle surrounding the joint." Given that a larger muscle mass can shield and cushion the knee from the mechanical forces within the joint, the researchers anticipated that individuals with more robust muscles would be less likely to develop the condition compared to those with weaker muscles. "That's precisely what our data showed," van Meurs confirmed. "When individuals had a greater muscle mass, the heightened risk of osteoarthritis associated with weight-bearing sports was virtually eliminated."

Dr. Kathryn Miller, an associate professor of internal medicine at the University of Wisconsin School of Medicine and Public Health in Madison, who was not part of the study, commented on the significance of this discovery. "The notion that muscle mass is crucial for joint protection has long been acknowledged," she said. "This study adds to the body of evidence suggesting that muscle mass is not only essential for joint function but may also reduce the likelihood of osteoarthritis development."

While the study's findings are significant, there is still much to learn, according to van Meurs. For instance, it is well-established that body weight is the primary risk factor for knee osteoarthritis. The data analyzed by van Meurs and her team was derived from individuals with an average body mass index (BMI) of 26, which is slightly above the healthy range but lower than the average BMI in the United States. The question remains whether the study's conclusions can be generalized to those who are overweight or obese. "We are not entirely certain," van Meurs stated. "A high BMI is a significant risk factor for the development of knee osteoarthritis. If it dominates so strongly, the influence of other factors might differ."

Miller concurred, noting, "The higher your BMI, the greater the stress you impose on your joints, particularly during weight-bearing activities. It's possible that individuals with higher BMIs may require even greater lower-limb muscle mass than those with lower BMIs to counteract the increased stress."

A substantial study currently underway at Erasmus Medical Center aims to determine if physicians can tailor their recommendations to patients based on their muscle mass, weight, and joint movement. "We are examining how much load individuals can place on their joints, considering these factors," van Meurs said, highlighting that many patients with knee pain inquire about the safety of continuing their preferred activities. At present, there is no definitive answer.

Despite the uncertainties, the study provides valuable insights. "Before engaging in substantial weight-bearing activities, consider gym training to fortify your leg muscles," van Meurs advised. And for those looking to start a weight-bearing activity like running, it's essential to begin gradually. "Not only your muscles but also your tendons need time to adjust to these new stresses to prevent immediate injury," she warned.

Miller encourages her patients to maintain a healthy body weight and stay active. "If you're diagnosed with osteoarthritis, don't cease your activities," she said. "Individuals who lead sedentary lifestyles tend to have poorer joint health and muscle mass, increasing their risk for symptomatic osteoarthritis." She suggests activities such as walking, wall sits, or performing chair stands without using your arms for support. The key is to keep moving. "Our advice to osteoarthritis patients is that if an activity causes mild discomfort that subsides quickly, it's acceptable," Miller said. "However, if an activity results in severe pain that persists beyond the next day, it might be too strenuous for your joint at this time."

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