Well, that was my understanding after speaking with several individuals who had knee problems. Here is what I found by googling knee problems and cycling:
"In comparison with other exercises cycling is a relatively ‘knee friendly’ activity that can help to improve knee joint mobility and stability. Cycling is frequently used as a rehabilitation exercise modality after knee injury or surgery as well as part of the management of chronic degenerative conditions such as osteoarthritis. The bicycle has a number of features that make it a particularly good tool for knee rehabilitation:
http://www.cartilagehealth.com/cycling.html#
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