Exercise that is good for the heart is not detrimental to the knee joint.
---Flavia M. Cicuttini, PhD and colleagues*

Well that's good news. I was just debating tonight whether to take my right knee to step aerobics tomorrow or not. One deep knee bend over the sprinkler system three weeks ago left me with screaming pain from the lateral meniscus. It's much better now--who knows why--and I wondered if it was sheer folly to step out to a little music much needed by me for the heart and the soul.

Dr. Cicuttini et al studied nearly 300 adults over 10+ years. At study's end, their knees were, on average, 58 years old. The investigators correlated their activity logs with the amount of cartilage still clinging to the top of their tibiae on the bottom of their knee joints. Those who particpated in more frequent vigorous exercise in the years prior to the study had a significantly larger chunk of residual cartilage compared with those who sat out the decade on the couch. And the best predictor of defect-free cartilage was each individual's current participation in vigorous exercise.
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*Racunica TL, et al "Effect of Physical Activity on Articular Knee Joint Structures in Community-Based Adults" Arthritis Rheum 2007; 57: 1261-1268.