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.

“There are things that we know of that cause osteoarthritis that can’t be modified like age or being female. But something like obesity or quadriceps strength is modifiable. You can actually do something about this. So the fact that we have something we know is related to risk and we know people can do something about it is exciting,” Dr. Segal adds.  

In addition to the finding that strong quadriceps muscles protect women, this study was one of the first of its kind to look at the effects of quadriceps strength in men.

Researchers discovered that strong thigh muscles didn’t seem to make as much of a difference in men developing osteoarthritis symptoms, though they aren't sure why.

Experts said the study should send a strong message to women.

“The reason why this study is important is because it shows if you try to maintain good muscle strength, your risk of your knee hurting because of osteoarthritis, is less,” says Mary O’Connor, MD, an orthopaedic surgeon at the Mayo Clinic in Jacksonville, FL.

Dr. O’Connor says this research supports her long-standing belief that patients, especially women, not only need to be more active, but need to do weight lifting exercises too.

“They shouldn’t feel intimidated, because they may be older, about learning how to use the equipment and working on building their muscle strength,” she says.

Dr. O’Connor also says, while this study talks about warding off osteoarthritis, those who already have the condition can also benefit from the message about keeping your muscles strong.

“It’s intuitively obvious. One of the problems is that patients get in a downward spiral where they hurt if they move and then they don’t move and then they get weaker and then there’s less support to their knee joint so they spiral down,” she says. 

“In my perfect universe, everyone would have an exercise routine that would include lifting weights two or three times a week," Dr. O'Connor says. "Lifting weights within their own personal ability to do so. Everyone can lift weights. Everyone can do something."