I've run marathons and walked two, deliberately - the Manchester Shine walks, and I was worse off for injuries etc after the walk this year, I walked it in 6:15 and finished with blisters and soreness in hips and knees, running is infinitely more comfortable, I'm happy to run a marathon knowing I will be a little stiff that evening but right as rain in a day or two. Besides if we all listened to the Doc, none of us would ever run