Last reviewed February 27, 2013
There's a joke I heard when I first started studying arthritis: A 90 year-old man sees his doctor complaining of pain in his knee. His doctor asks him, "What do you expect? You're 90 years-old." The old man replies, "Yes, but my other knee is also 90 and it feels fine."
That pretty much sums up why "wear and tear" arthritis is not an accurate description of osteoarthritis (OA), or degenerative joint disease. Just because you live a long time, doesn't mean you'll inevitably wear out your joints.
Why Your Joints Aren't Like Tires
Degenerative joint disease is more common with aging, so it may seem logical to assume osteoarthritis is due to "wear and tear." It's also true that extreme or unusual stress on joints can cause damage that leads to osteoarthritis. But for most people, arthritis due to normal wear and tear is a myth. Your joints aren't like a car's tires or a light bulb that inevitably wears out over time with enough use.
Osteoarthritis occurs when the smooth, shiny cartilage that lines the joint deteriorates. In some cases, this can happen after an injury but for most people it's a result of aging and genetics. The most common locations for osteoarthritis are the:
- Finger and toe joints
- Upper and lower spine.
One thing we know for sure about osteoarthritis — it's very common. An estimated 21 million people in the United States alone have OA. If you're fortunate enough to live to age 75 or older, chances are perhaps as high as 70% to 90% that you'll have OA in at least some joints. With these numbers staring at you, it's reasonable to wonder if there's something you can do to prevent it. Specifically, should you limit your activities so you don't "wear out" your joints?
Back to top
Is Exercise the Culprit?
For most people, exercise is a good thing. But at what point does exercise do more harm to joints than good? Are running and jogging actually harmful for the knees or other weight-bearing joints? Does exercising too long or too intensely damage the joints?
Clearly, running stresses the weight-bearing joints. In fact, up to 5 to 7 times your weight is supported by your knees while jogging. Weight-bearing joints are subject to even higher stresses with jumping or suddenly starting and stopping over and over. Although the research is mixed, long-term runners are not clearly more likely to wear out their weight-bearing joints than people who are sedentary.
For example, a large study of runners published in 1998 found that over a nine-year period, members of a running club ages 50 and older had no higher incidence of OA than an otherwise similar group of non-runners. A more recent study came to a similar conclusion. Runners averaging 3.5 miles of roadwork each day had 25% less musculoskeletal pain than those averaging just 2 miles each week.
A little soreness might be worth suffering through if you enjoy running (or other physical activity) and want the cardiovascular benefits. But sudden, severe injury (a fracture or ligament tear) from repetitive use can cause cartilage damage that can lead to osteoarthritis even though it may take years for it to develop.
That's why experts recommend that you avoid sudden increases in how far or how fast you run so that you don't develop a stress fracture. Here's what happens. The repeated pounding of running causes a bone in the foot or leg to break because it can't repair itself as fast as it is injured. This is one example of "overtraining," or exercising so much that an injury follows.
So, if you are training for a special event, such as a marathon or tryouts for the lacrosse team, you probably need to dial your training up a notch or two. To avoid a stress fracture or other injuries related to overtraining, follow these two rules of thumb:
- Don't increase your effort by more than 5% to 10% per week. For example, if you've been comfortable running 3 miles in 30 minutes (10-minute miles) five days a week, don't suddenly start running eight-minute miles. You might be able to do it, but you may pay for it.
- Don't increase your distance and speed at the same time. Change one or the other, and do it gradually. If you notice pain or discomfort in one part of your body that doesn't promptly improve with rest, back off — you may be pushing things too fast.
When it comes to the question of joint-use and osteoarthritis, it's important to distinguish a sudden, severe injury like a fracture or ligament tear, from a repetitive-use injury that can occur from running, for example. A joint fracture may lead to osteoarthritis years later. So, for people who are not participating in highly competitive activities in which acute injuries are common, there is no clear connection between repetitive use and osteoarthritis.
Back to top
Consider Your Hands
Perhaps the best argument against a direct connection between use (or overuse) and osteoarthritis is when OA affects the hands. Finger joints with OA look very similar to the knees with OA, yet we don't bear weight on the hands — at least I don't. There's also the observation that "handedness" doesn't play a part in osteoarthritis. If 90% of people are right-handed and if osteoarthritis were purely use-related, there ought to be a lot more right-hand arthritis compared to left-hand involvement. That's simply not the case.
Hand OA is a good example of genetics at work: If your parent or other first-degree relative has OA of the hands, it markedly increases your risk of the condition.
Back to top
Protecting Your Joints From Stress Versus Disease
"Use it or lose it" is certainly a concept that applies to the joints. The fact is, joints were meant to be used. A condition appropriately called "frozen shoulder" can develop within a week or two if the shoulder doesn't move, even if there was no injury involved! That's a good reason to avoid using a sling for prolonged periods and why range of motion exercises are so important after an injury or surgery. It's also why people who already have arthritis are encouraged to keep moving.
The concept of "joint protection" is typically applied to people who have arthritis as a way to encourage use while avoiding excessive stress on the joints. For example, rather than carrying a heavy load with your hands, rest it on your forearms and use your arms rather than hands to carry it. The same concept is applied to exercise — swimming or biking provide excellent cardiovascular exercise that is easier on the joints than jogging.
These measures may lead to less pain or stiffness — that is, they may protect you from joint pain by avoiding stress to the joints. Unfortunately, that's not the same as protecting the joints from deterioration, which joint-protection measures cannot reliably accomplish.
Back to top
What Causes OA?
If OA is not caused by wearing out the joints, what causes it to develop? The answer varies, depending on whom you ask and whose joints you ask about. In fact, there is often no single cause that can be identified. There may be several potential explanations. Often there is no reasonable explanation at all.
The most common risk factors for osteoarthritis include:
- Advanced age
- Family history – Up to 50% of osteoarthritis is thought to be related to inherited tendency to develop joint degeneration
- Injury – especially a fracture that involves the joint)
- Rheumatoid arthritis (or other diseases that cause chronic joint inflammation)
However, these are risk factors, not causes. Plenty of older, overweight people never develop OA.
Back to top
The Bottom Line
If you're worried about "using up" your joints, remember that there is not a limit on the number of times you can make a fist and there is no "shelf-life" for the knees. From my reading of the available research, it's much better to be physically active than to hold back to protect your joints. If they aren't bothering you with the activities you're doing, it's unlikely you are harming them. Perhaps someday you'll have 90 year-old knees that serve you well and feel just fine. But if you do develop arthritis, don't blame the exercise. In the absence of significant injury, it might make more sense to blame your parents.
Back to top
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.