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I am often asked whether physical activity has a positive or negative effect on the overall health of knee cartilage. The answer is unclear. Published data are conflicting.
What is known and generally agreed on:
1) Physical activity has been shown to facilitate cartilage development in children
2) Forced immobility (spinal cord injury) results in rapid cartilage loss
3) The medial knee compartment experiences significant mechanical loads during weight-bearing activity and is often the primary site of knee OA
A recent study attempted to answer whether 1) long-term (10yrs) participation in vigorous physical activity would benefit knee cartilage in healthy adults and 2) whether there were certain subgroups with asymptomatic preexisting structural knee changes which predict a harmful cartilage response to long-term physical activity.
Vigorous = activity generating sweating or SOB at least 20min 1/wk
Healthy older adults (mean age 57.8 yr) performing persistent vigorous physical activity had an increased risk (odds ratio 1.5) of worsening medial knee cartilage defects but not of a change in cartilage volume
In those w/ asymptomatic preexisting structural knee changes, there was worsening of cartilage defects (odds ratio 3.4) and a trend toward increased rate of loss of cartilage volume (again in the medial knee compartment)
Long-term effects of vigorous physical activity may depend on the preexisting health of the joint
References
Teichtahl, A.J., et al. Effect of long-term vigorous physical activity on healthy adult knee cartilage. Medicine and Science in Sports and Exercise. June 2012