With running season in full swing, I've had a number of knee and hip complaints stop by the clinic. I also volunteered at a local triathlon where a few injured competitors checked in with knee, hip or low back pain. Some of the questions I get with these types of injuries are; "I'm suffering from wear and tear on my joints, do you think I should stop playing or competing?"
Many of these people are told that they will further injure their joints (knees, hips and back) if they continue to play or compete, so they should just stop whatever sport they are doing. The problem with this is that many of these people are playing or competing at something they love doing. Why would you want them to stop doing it? The second problem is that you are asking them to become less active or inactive. To give up running, soccer, tennis, or whatever sport to and to take up knitting (not that there is anything wrong with knitting.)
From my experience, there are two things that are bad for joints: Mis-use and Dis-use.
MIS-USE
The best example of misuse would be using a spoon to shovel a ditch (or in the case of a movie like Shawshank Redemption, a rock pick to dig yourself out of jail). Its the wrong tool for the job. If you were to choose the correct tool, you would accomplish the job much more efficiently as well as not end up with a worn out, bent spoon. The knee for example, is meant to be bent in a front and back direction. It is not meant to be bent in a side to side direction. If you watch some people run, sometimes you can see their knee fall inwards (especially when they get fatigued). This is an example of MIS-USE of the knee and will cause subsequent wearing of joint surfaces and lead to problems in the future.
DIS-USE
Its pretty clear that if you don't use it, you will lose it. This happens to your car if you park it for a long time, then jump in it and expect it to work like it use to. I'm no mechanic, but what you will find is that the joints in the car are dry, the engine may take some time before it runs smoothly, and the breaks may not respond as quickly as they use to. However, if you use the car, it seems to keep everything moving fluidly (maintenance care is also a good idea...for the car and your body!). For the body, bones respond to stress. If you place small amounts of stress on your bones (from weight bearing exercises) bone will become harder and more resilient. The example of dis-use can be seen in the elderly population who is less mobile (those in wheelchairs or confined to beds). Their bones are found to be more brittle from a lack of use. Thus, this is the population that tends to end up with fractured hips from falls when compared to a younger (more active) population. This DIS-USE not only causes bone degeneration, but causes the cartilage that lines the joints to dry up.
So instead of having to quit competing or playing a sport, it is better to figure out how to use your joints properly so you can maintain them for the future. Just look at those who are in their 60's, 70's and 80's and are still actively playing, running and competing! I look at some of the older competitors from the triathlon this past weekend and I hope that I can do what they do when I reach their age!