I was recently reading about a presentation put forth at the North American Radiological Society by a Research Fellow at the University of California San Francisco, which you can find here. Though this article concludes moderate activity may be the key to saving knees, this article also suggests that too much exercise led to early degenerative cartilage changes in the knees of healthy people aged 45 – 60 and in those at risk for osteoarthritis on examination of the structural changes of the knee using MRI over a period of 4 years.
I would argue, however, that for the average Canadian, sedentary lifestyles are perhaps more problematic and more prevalent in our North American population compared to those who participate in too much movement as evidenced by the numerous accounts of the increasing weight epidemic and diabetes, or “diabesity” problem.
Before you jump to the conclusion that too much exercise indeed predisposes a person to early degenerative knee changes, in defence of the importance of exercise, it may also be important to know that population in this study were at high risk for knee osteoarthritis because of family history, obesity, and/or a history of knee injury or replacement surgery.
Lin, W. et al. (2012). High levels of physical activity are associated with greater cartilage degeneration over a period of 4 years as assessed with T2 relaxation time measurements – 3T MRI data from the Osteoarthritis Initiative. Radiological Society of North America.