I actually switched to a treadmill and took a course in running and minimalist shoes (which I thought were BS before) and changed my running form. Got rid of my shin splints and knee pain. No impact issues... was a weird transition, though. Learning to run like a boxer stands was more difficult than I thought it would be. I can run for about a mile, mile and a half on the concrete, outside before I realize I'm doing damage and have to stop... getting old sucks =) I do have a bike, but somehow it doesn't do the same disassociation for me. Not sure why. I think it has to be something I hate, personally, to get me over the hump and force me out of my own body.