The main difference I can think of between a marathon and shorter distances is the glycogen 'wall' - something that won't happen on a run of less than 20 miles. There's also the whole fact that four hours of stress and strain on your joints and muscles and feet is somewhat worse for your body than ten minutes.<p>(Having said that, I don't see the point in twisting statistics to lambast marathons either. I plan to run my first one next year regardless!)