Strengthening my feet/arches

[Pookie]

I am a life-long lover of running who has dreamt of becoming an ultramarathoner over the past two years, but who has also struggled through two knee surgeries in the past eighteen months. Doctors have begun to blame my concaving arches as part of my chronic injury pattern, which involves my feet and ankles in addition to my knees. I have invested a great deal of money in running sneakers and custom orthotics.

I recently read an article in Men's Health by Christopher McDougall titled, "The Men Who Live Forever." I was encouraged by McDougall's description of the Tarahumara Indians and of American miler Alan Webb, who consciously work to strengthen their feet. I am seeking more information on how to strengthen my own feet so I can apply it to my running. Now that my knees are "fixed," I'd much prefer to actually "fix" my feet as well, rather than relying on crutches like orthotics.

Do you have any reccomendations for how to build the muscles in my feet, so my arches will stop collapsing? The article is vague on how to actually achieve this goal.

Any help you can provide is greatly appreciated. I seem to have the lungs and heart for long distance running, but I need help fixing my feet and my gait for this dream to become reality.