Exercise and your joints

Regular exercise has enormous benefits for health. Most importantly, it will reduce the risk of heart attack, stroke, and premature death. And if that's not enough for you, consider the many studies that link physical activity to protection against diabetes, obesity, high blood pressure, osteoporosis and fractures, depression, insomnia, dementia, colon cancer, breast cancer, and possibly prostate cancer.

Despite all these benefits, only about a third of American adults get the exercise they need. Couch potatoes have many excuses to explain their sedentary ways. Lack of time is the most common, and the belief that exercise is too hard is a close second. But since moderate exercise that can be built into daily life is all it takes to promote health, neither excuse is very convincing.

Another common excuse is a little harder to dispel. It's the belief that exercise causes arthritis. Even if it were true, it might be wise to accept aching knees as the price for a healthy heart, brain, and metabolism. But studies show that exercise can be safe for joints, both in older, overweight folks and in athletes.

The knees of Framingham

In 1948, more than 5,200 residents of Framingham, Mass., volunteered for the Framingham Heart Study, which has produced major insights into the causes of heart attack and stroke. In 1971, scientists began a new study of the children of the original volunteers and the spouses of those children. Between 1993 and 1994, 1,279 members of the Framingham Offspring Cohort enrolled in a study of exercise and arthritis. Their average age was 53.

All the volunteers were free of arthritis when the study began. Each answered detailed questions about their patterns of exercise, including walking, jogging, being active enough to work up a sweat, and their overall exercise level. All the people provided information about knee injuries and symptoms of knee pain and stiffness. In addition, all the volunteers were weighed and measured, and they each had a full series of knee x-rays.

Between 2002 and 2005, the subjects answered the same questions about knee pain and injury, and the x-rays were repeated. All the x-rays were independently evaluated by two experts who had no knowledge of the subjects' exercise histories.

When the results were tallied, the researchers found no link between exercise and arthritis of the knee. The most active people had the same risk of arthritis as the least active, both in terms of symptoms and x-ray abnormalities. Exercise was as friendly to the knees of joggers as walkers, even though jogging subjects the lower body to much higher impact and stress than walking. And even though obesity is an independent risk factor for arthritis, physically active overweight members of the study group fared just as well as their slim peers.

Australian knees

Although the Framingham study goes a long way toward dispelling the idea that exercise causes arthritis, it did not confirm a fond hope of exercise enthusiasts. Osteoarthritis begins when the cartilage that cushions the joints begins to wear away. Because cartilage does not have its own blood supply, it must get its nutrients from the joint fluid that bathes it. Exercise compresses joints, forcing more nutrient-rich fluid into cartilage. Perhaps, then, repetitive exercise is good for joints.

The Framingham study did not find any protection, but a high-tech investigation from Australia did. Researchers studied 297 men and women who were between the ages of 40 and 69 when the study began in the early 1990s. All were healthy, and none had histories of knee injuries or disease. The volunteers were weighed and measured, and they provided detailed information about their exercise habits and joint symptoms. The evaluations were repeated between 2003 and 2004, and each subject had a knee MRI. The results showed that people who performed the most vigorous weight-bearing exercise had the thickest, healthiest knee cartilage.

Runners' knees

The Framingham study is important because it evaluated a group of ordinary people — middle-aged, often overweight, and not overly athletic, just like many of us. But a 2008 study that compared 284 dedicated runners with 156 nonrunners also found little evidence that exercise causes arthritis. After a remarkably long 21-year follow-up period, the runners experienced significantly less musculoskeletal disability than did their less active peers — and the runners also enjoyed a 39% lower mortality rate.

The research is impressive, and it confirms earlier studies. Former varsity runners, for example, are no more likely to develop arthritis in their legs than former college swimmers, and champion runners are no more likely to end up with arthritic hips than nonathletes.

Exercise as therapy?

Exercise is often prescribed for patients with arthritis. Exercise may be safe for healthy joints — but is it also safe for arthritic joints?

In 2005, British researchers evaluated 13 randomized clinical trials that compared walking, muscle-strengthening exercises, and conventional therapy without exercise in patients with osteoarthritis of the knee. Both walking and muscle-strengthening were safe and effective, reducing pain and disability. And in 2006 and 2007, scientists in the Netherlands and the U.K. reported that graded exercise programs are safe and effective for patients with arthritis of the hip or knee.

Healthy body, healthy joints

Exercise is good for health. Still, it can have side effects. To prevent problems, be sure your general health is good; older people and patients with heart disease, hypertension, diabetes, or other significant problems should get medical clearance. And all of us should get in shape gradually. Above all, listen to your body as you exercise your way to health, and be sure to report any signs of discord to your doctor.

Warming up and cooling down will help protect your heart and your joints. Stretching exercises, good shoes, and good technique will also reduce your risk of musculoskeletal injuries. With these simple precautions and a dose of common sense, exercise will be safe for your joints.

Next excuse?