Last reviewed by Faculty of Harvard Medical School on January 24, 2013
By Harvey B. Simon, M.D.
Harvard Medical School
Regular exercise has enormous health benefits. Most importantly, it reduces the risk of heart attack, stroke and premature death. And that's not all. Many studies link physical activity to protection against:
- High blood pressure
- Osteoporosis and fractures
- Colon cancer, breast cancer and possibly prostate cancer.
Despite all these benefits, only about one in four American adults gets the exercise they need to promote health. People have many excuses for not exercising. One excuse concerns the belief that exercise causes arthritis. Is this true or not?
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Excuses, Excuses, Excuses
Couch potatoes have many excuses to explain their sedentary ways. Lack of time is the most common. The belief that exercise is too hard is a close second. But neither excuse is very convincing. All it takes is 30 minutes of moderate exercise nearly every day to promote health.
What about the arthritis excuse? Recent studies show that exercise can be safe for joints, both in older, overweight folks and in athletes.
Even if it were true, it might be wise to accept aching knees as the price for a healthy heart, brain and metabolism (cholesterol, blood sugar, body fat and muscle).
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Should Runners Worry?
Running, in particular, is considered to be hard on the body. Unlike walking, running is a high-impact exercise. It's simply a matter of gravity: What goes up must come down.
Walkers have one foot on the ground at all times, while joggers and runners are entirely airborne for part of every stride. Each time a foot hits the ground, it puts a stress equal to eight times the body's weight on a person's feet, legs, hips and neck. In just one mile, a runner's legs will have to absorb tons and tons of force from the impact.
Running actually causes relatively few physical problems. It's a testament to the wonderful construction of the human body. The faster the pace, however, the greater the impact and the greater the risk of injury. But that doesn't mean that running will cause arthritis. In fact, new studies provide reassurance that exercise, and particularly running, are safe for healthy joints. Exercise may even help joints stay healthy.
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What the Research Shows
Framingham Offspring Cohort
In 1948, more than 5,200 residents of Framingham, MA volunteered for the Framingham Heart Study. This study has given us 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. The average age of participants was 53.
All of 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. Everyone provided information about knee injuries and symptoms of knee pain and stiffness. In addition, participants were weighed and measured, and had a full series of knee X-rays.
Between 2002 and 2005, the subjects again answered questions about knee pain and injury and had another set of X-rays. All the X-rays were independently evaluated by two experts who didn't know 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 important risk factor for arthritis, physically active overweight members of the study group fared just as well as their slim peers.
High-Tech Australian Study
The Framingham study goes a long way toward dispelling the idea that exercise causes arthritis. But it did not confirm the hope that exercise might actually be good for joints.
In osteoarthritis, the most common form of arthritis, the cartilage that cushions the joints starts 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.
Australian 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 had no 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; each subject also had a knee MRI.
The results showed that people who performed the most vigorous weight-bearing exercise had the thickest, healthiest knee cartilage.
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The Knees of Long-Distance Runners
The Framingham study is important because it evaluated a group of ordinary people just like many of us: middle-aged, often overweight, and not overly athletic adults. But how about serious long-distance runners? A 2008 study that compared 284 dedicated runners with 156 non-runners found little evidence that exercise causes arthritis. After a remarkably long 21-year follow-up period, the runners actually experienced significantly less musculoskeletal disability than did their sedentary peers and the runners also enjoyed a 39% lower mortality rate.
The new research is impressive and confirms earlier studies. Former varsity runners, for example, are no more likely to develop arthritis in their legs than former college swimmers. Champion runners are no more likely to end up with arthritic hips than non-athletes.
If exercise is so safe for joints, why do so many retired football players appear in advertisements for arthritis medication?
The answer is traumatic injury. A joint injury can seem to heal completely, but residual damage can slowly progress to arthritis later in life.
A study of 1,321 Johns Hopkins Medical School graduates proves the point. Nearly 14% of doctors who suffered hip injuries during their student years developed hip arthritis by age 65. Only 6% of those without hip injuries developed arthritis. A knee injury in youth was even more significant, producing a fivefold increase in the risk of arthritis of the knee in adults.
With care, jogging and running can be safe and enjoyable. The main rules are familiar: Start slowly, build up gradually, alternate harder and easier work outs, and listen to your body. Here are a few additional tips: