>I'm happy to walk at high speed, but I'd like to have these knees for another 40-50 years, so have no intention of running on them.
>
>Have you considered an elliptical machine? It gives a better workout without the joint impact. If you're willing to spend $, the ones from Octane Fitness are exceptional and worth every cent IMHO if you're planning to remain mobile for another 50 years.

My husband uses an elliptical; I'm happy on the treadmill. We belong to a gym, so don't have to buy machines.

Tamar