Elliptical Trainers

I read somewhere that our knees are made to climb stair not come down stairs. It states that coming down put stresses on the knee because you are holding back. Is this true? If so, is going reverse on an elliptical trainer bad for you?

P.S. I tried to research this on Internet but I couldn’t find anything.

Nobody??

Only anecdotal, but I found the elliptical trainer very useful while recovering from arthroscopic knee surgery last year.