A study finds that stronger quadriceps muscles may protect women, but not necessarily men, from the pain and stiffness of osteoarthritis in their knees.

Osteoarthritis is the most common type of arthritis, affecting an estimated 26.9 million adults in the United States, according to the Centers for Disease Control and Prevention, and the knee is the joint most commonly affected by it. More women get knee OA than men.

In this study, researchers from the University of Iowa Hospitals and Clinics followed 3,026 men and women between the ages of 50 and 79 for 30 months.

They took x-rays at the beginning and end of the study to determine the presence of osteoarthritis, and they used a device called an isokinetic dynamometer to measure the strength of different muscle groups. They also asked participants about their levels of pain, aching or stiffness at the beginning and end of the study.

At the end of 30 months, 48 of 680 men and 93 of 937 women developed osteoarthritis detected by x-ray, and 10.1 percent of women and 7.8 percent of men displayed signs of symptomatic knee OA.

But the women with the strongest quadriceps muscles, the muscles on the front of the thigh, had the lowest number of cases of knee osteoarthritis and appeared to be protected against pain and stiffness.

The study was published in Arthritis Care & Research.

Neil Segal, MD, is the director of the Clinical Osteoarthritis Research Program in the Department of Orthopedics and Rehabilitation at the University of Iowa in Iowa City.

He says if you split the study group into thirds, based on those with the most strength, middle and weakest, the group with the most  strength had approximately half as much chance of getting symptomatic knee osteoarthritis as the weakest third.

 “This finding is quite important for public health. We predicted who would be developing pain and stiffness in their knee on most days and that’s what really matters to people and if it will hurt,” Dr. Segal says.