Are you talking about solely walking as opposed to run/walk?
If so, I have some experience with this. This past October, I did the Jimmy Fund Walk that follows the Boston Marathon course. I trained for it using run/walk, but on "race day," I was getting a sharp pain in my knee for a few seconds every time I transitioned from a walk to a run, so I did A LOT more walking (and significantly longer walk intervals) than I originally planned. With a 12-hour time limit, finishing wasn't an issue (I'm a relatively slow walker), but I did find out a few things:
- Walking a marathon is no easier than running one. In fact, if you are only walking, you have the same problem that constant runners do - you are using the same muscles in the same manner for 26.2 miles. When you run/walk, you are moving your body differently at different times and it helps combat muscle fatigue.
- You really, really, REALLY need to have the longer mileage walks. Because I was using run/walk, I was missing the extra time on feet. My finish time was over an hour longer than my longest training run and that last hour was really, really ROUGH. The first thing I said to my coach afterward was that this was so much different than run/walking a marathon. If I had planned on walking this, I would have wanted my training to be very different.
Are there people that walk the Disney Marathon? Absolutely yes. But the difference between training for a half marathon and training for a marathon (be it running, run/walking, or walking) is HUGE! I say this every year when it comes to the marathon, Goofy or Dopey - there are things that you can "get away with" on a half marathon that will come back and bite you HARD when you are doing 26.2 miles.