Rapoport 2010 performed an analysis of marathon runners. He notes that tens of thousands of people run them every year and yet, most experience severe metabolic limitations from poor fueling or running at the wrong speed while 1-2% simply cannot finish the race.
Interestingly, the risk factors for hitting the wall or ‘bonking’ as it is referred to by the marathon community are being male, running less than 32km in training and expecting to hit the wall. Thus, beating the wall as focused on training and energy management.
Rapoport took a different approach. He noted that it is generally estimated that it takes 1kcal per kg per km to run. Thus, a 70kg individual running 42km, needs approximately 2950kcal. Now, we know that fat stores provide 9kcal/g and the author points out that even a mere 2% of bodyweight in fat could fuel a 180km race. The problem is of course the limited carbohydrates available for the metabolic process. An average adult liver holds 88g of carbs and can hold if loaded maximally 160g of carbs. This would translate to anywhere between 350 and 650kcal of carbs.
Rapaport continues exploring % of VO2 one should run at and how one should pre-fuel and peri-fuel. He has gone on by using equations for the relationship between aerobic intensity and which fuel (fat or carbs) is the main substrate for energy, aerobic intensity and running speed, aerobic capacity, max running speed during a marathon, etc. to build an entire system of relationships to determine how fast one should run a marathon at, what fuel to refuel with and how to pre-fuel.
These equations, while highly involved and require some dedication to work through, can help both first time runners and veterans of the marathon world alike. Plugging in the known numbers from famous marathoners (such as Evans Rutto) and one gets numbers within a few minutes of his best recorded times.
This new information is promising and we hope to see it used by others and reproduced. This could change the trial and error method of carb loading and peri-refueling to a more standardized scientific pursuit.