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.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
