Normal healthy cartilage is built for exercise, to include loading bearing exercise such as running. There is good evidence that chondrocytes, the cells that maintain the cartilage matrix, actually grow better in response to pressure- certain chambers (called bioreactors) have been designed to promote cell growth under these conditions.
It is therefore with mixed emotions that I sometimes advise patients to exercise less, or at least to consider a modification of what type of exercise they are performing. This apparent contradiction comes because cartilage that is damaged already is not the same as normal, healthy cartilage. In spite of many advances in cartilage repair, it is just not appropriate to think that any repair is as good as the original.
Advice for professional athletes may be somewhat different than advice for the ordinary athlete or the ordinary person. If someone is getting paid to perform a sport- or, indeed any type of work- it is not uncommon for them to expose themselves to risks that would not normally occur to other people. This is true whether we are talking about an astronaut or a coal miner or an oil rig worker. As a general rule, professional athletes are very protective of their bodies even though they purposely expose themselves to risk; and they understand the consequences of injury.
One frequent problem is that certain recreational athletes take themselves quite seriously;
they want to be treated as if they were professional athletes-, which they are not. This is a common situation that disconnects expectations from reality and should be discussed before cartilage repair is attempted. Almost any surgical solution can be subverted by a patient who does not comply with the post-operative rehabilitation plan. It would be better for all concerned for such a person not to have surgery.
Rehab regimens are individually tailored to each specific situation. Most include a period of limited or non weight bearing, followed by a gradual increase in loading activities. Early swimming is a feature I really encourage. Where some patients fall off the path is somewhat later on, when they are typically feeling good, and think that just because they feel better that the cartilage repair is progressing more rapidly than expected. Some people think they are superman! A better view is that cartilage repair is a biology experiment we are conducting inside the body, and that time is an important parameter– often more important than symptoms.