In the PLoS computational Biology article 'Metabolic Factors Limiting Performance in Marathon Runners,' marathoner and Harvard Ph.D. student Benjamin I. Rapoport states that 40% of marathon runners hit 'the wall.'
His research has found that long distance runners can prevent their bodies from hitting the wall by running at a specific pace and consuming specific amounts of carbohydrates at specific times during the race.
An interesting tidbit from his research is that he cites a study that find the primary risk factors for ‘hitting the wall’ are male gender, running a maximum distance of 20 miles or less during training, and expecting to ‘hit the wall.’
To read the study 'Hitting the wall in the marathon: Phenomenological characteristics and associations with expectancy, gender, and running history,' click here: http://www.sciencedirect.com/science/article/pii/S1469029207000246
To find out your personalized carbohydrate fueling needs, use Rapoport's running endurance calculator - http://endurancecalculator.com