Strong quadriceps muscles -- those at the front of the thigh -- are a must for anyone who wants to fly downhill on skis, attempt a double axel on skates or scale a mountain by foot or by bike. These muscles do more than help you straighten your legs and stand; they're integral in everything from walking to high jumping.
But they may have special importance for people with knee osteoarthritis.
A recent study of people with the condition found that those who had stronger quadriceps had less cartilage loss behind the kneecap. Less cartilage loss can mean better range of motion and less discomfort.
"Although this was not an exercise study, our results suggest that [exercise] is beneficial for the knees, especially the knee joints," says Dr. Shreyasee Amin, assistant professor of medicine at the Mayo Clinic in Minnesota and lead author of the study. "Other studies have shown that it can help with decreasing pain and improving function."
Most experts agree that excess weight, injury and a genetic predisposition contribute to knee osteoarthritis, but they're less sure about the effect of various types of exercise. They point out, however, that strengthening the quadriceps could prevent further damage.
"It helps stabilize the patella [a flat, triangular bone covering the surface of the knee joint] and prevents it from moving laterally and tracking abnormally in the knee," Amin says. "When it's not aligned in the knee groove properly, you can have more cartilage loss from the friction."
Osteoarthritis in general, in which the cartilage between bone joints is worn away over time, is primarily associated with aging and affects some 21 million Americans, according to the Arthritis Foundation. Knee osteoarthritis accounts for many of the almost half-million knee replacement surgeries each year.
The study, presented this month at the annual meeting of the American College of Rheumatology, was done in conjunction with researchers from Boston University and UC San Francisco. It included knee-joint MRIs of 265 men and women with the pre-existing condition who were tested again at 15 months and 30 months to see how much cartilage had been lost over time. Participants' quadriceps strength was also measured during knee extensions, a seated exercise in which the legs are lifted in front of the body.
Those who had the strongest quadriceps had the least cartilage loss at the patellofemoral joint behind the kneecap, Amin says. Those with the weakest quadriceps had about 20% cartilage loss over time, whereas those with a medium amount of quadriceps strength had just slightly more. The strongest group had about 60% less deterioration than the weakest group.
Although most health experts recommend building up the quadriceps to prevent further osteoarthritis damage, previous studies have shown conflicting relationships between quadriceps strength and osteoarthritis progression. In some, stronger quadriceps had either no effect on progression -- or, for some, a harmful effect. One, published in the Annals of Internal Medicine in 2003, studied people with knee osteoarthritis who had malaligned knees (such as knock knees) or lax knees (excess motion in the knees). Among 237 people, more quadriceps strength resulted in a greater chance of osteoarthritis progression in the tibiofemoral joint, the main knee joint.
"There are a few studies that conflict," says Lynn Millar, professor of physical therapy at Andrews University in Michigan and fellow of the American College of Sports Medicine, "but if you look at the majority of studies, weaker quadriceps are related to increased problems with osteoarthritis. You can look at it two ways -- some suggest weakness precedes the osteoarthritis, others show that it occurs concurrent with it. But there are numerous studies that show that strengthening the quadriceps decreases pain and improves function and range of motion and doesn't progress the arthritis any faster."
Amin believes that maintaining quadriceps strength is good for the knees, especially for the knee joints. "It's not always clear what causes osteoarthritis -- certainly genetics, being overweight and injury contribute -- but exercise per se is not bad," Amin said, recommending continued exercise even for those who have the painful condition.
That can seem like a tall order -- some sufferers fear that exercise will cause more pain. "At first [exercise] may not be comfortable," Millar acknowledges, "but if you do a proper strengthening program, it will decrease the pain over time."
Arthritis can be a vicious circle, she says. "If it's hurting, you think you need to rest it. But the more immobile the joint is, the less nutrition gets to it."
The fluid the joints need to move is delivered through compression and relaxation of the joint -- "which is basically movement," Millar says. "If you don't move the joint, you'll start to deteriorate the joint surfaces."
Of course, exercise may have to be modified to prevent further damage of the joint. Runners, for example, may have to switch to walking, or water-based workouts. "It depends on the type of problem," Amin says, "but you want to try to avoid high-impact activities such as jogging, or high weight-bearing activities."
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Experts recommend these exercises to strengthen the quadriceps.
* For those who haven't exercised in a while or have never exercised, begin by rolling a towel up tightly. Sit on the floor or a bed, legs extended in front, and place the rolled towel under one knee. Contract the thigh muscle and push the back of the knee into the towel, straightening the leg. Hold for about six seconds, eventually working up to 10 repetitions, then more as the muscle becomes stronger.
"This is a really easy exercise -- we do these for people who have a lot of pain or swelling," says Jennifer Hootman, an epidemiologist with the Centers for Disease Control and Prevention in Atlanta and a certified athletic trainer.
* For those in better shape, sit in a chair and strap light ankle weights around the ankles. Straighten one knee, starting with two to three sets of six repetitions, eventually working up to two to three sets of 12 repetitions. Repeat with the other leg.
This exercise can also be performed by wrapping the end of an elastic band or tube around one ankle and tying the other end to a leg of the chair, Hootman says.
* Those who are used to exercising can also try a wall sit. Stand with your back against the wall, take about two to three steps away and slide your back down the wall to a 90-degree sitting position. (The out-ofshape should stop halfway between standing and 90 degrees.) Hold this position for about five seconds, working up to 30 seconds or longer, and toward that 90-degree angle, as the muscles get stronger.
These exercises, suggested by Lynn Millar, professor of physical therapy at Andrews University in Michigan, are an easy way to strengthen the quads without using equipment.
* For the gym rat, Millar suggests squats on a Smith machine, a barbell-weight machine with an attached, sliding bar that allows less pressure to fall on the knees than a free-weight barbell. Begin with low weight and repetitions and increase both as you progress.
People with existing knee pain or knee osteoarthritis should check with a physician before beginning any exercise program.
-- Jeannine Stein