Naturally, one should always give the knee joint and protecting the knee joint careful consideration. However, I believe that using a treadmill will not overtax or damage the knee joint any more than climbing hills around the CMU area, especially in the company of hippos. Still, it is important to raise this potential issue. As for me, I will not use a too-high incline without working up to it gradually, over a significant period of time. I will also not use the treadmill for running, jogging, or high-stress maneuvers. If you are able to show evidence, through providing a link, which demonstrates that using a treadmill, compared to hill climbing, is more likely to contribute to knee damage, or what you call some crippling effect, then... Please let me know, immediately. Thank you.