Exercise Poses Virtually No Danger to Your Joints

There is no good evidence supporting a harmful effect of regular exercise on normal joints, according to a review of studies.
Exercise is beneficial for weight control, management of cardiovascular disease and diabetes, and improving psychological well-being. However, there is also a perception that exercise is potentially harmful to joints, in particular those of the lower extremities.
Researchers reviewed existing studies on the relationship between regular exercise and osteoarthritis (OA) and concluded that in the absence of existing joint injury there is no increased risk of OA from exercise.Sources:
Eurekalert January 27, 2009
Journal of Anatomy January 21, 2009; 214(2): 197-207