Aside from the elite runners, I've always been impressed watching marathon finishers, and seeing what a variety of body sizes and shapes can go the distance, and how seldom looking at someone's shape could tell me how fast they were going.

When I coached novices to run a marathon, it was the overweight individuals who invariably were the best fundraisers, because so many people couldn't believe that they could run that far.

But I would certainly agree that extra weight puts an added burden on knees, ankles, backs, and hearts.