Sensible advice for aches, pains & injuries


Free tool calculates how fast you can run a marathon without hitting The Wall

Paul Ingraham ARCHIVEDMicroblog posts are archived and rarely updated. In contrast, most long-form articles on are updated regularly over the years.

This item is for the runners: a formula that tells you exactly how fast to run to avoid hitting “the wall.” Just plug in some information about yourself … and get back the Holy Grail of marathoning.

“The” wall is the point in a race when your carbohydrate reserves are exhausted, and about 40% of racers hit it — despite the fact that it’s what every marathoner most wants to avoid. It doesn’t have to be that way, says Ben Rapoport, an MD student at Harvard Medical School, a PhD student in the department of Electrical Engineering at the Massachusetts Institute of Technology, and a marathoner himself.

The metabolic math of fuel usage is quite precise and calculable in principle, but far from easy to do in practice. So Mr. Rapoport has created a handy computer program (freely available on the web) that can do it for you, taking into account a few basic variables — weight, age, resting heart rate, and target race time — and producing answers of great interest: estimated VO2max, and the carb loading, total calories, and pacing required to meet your goal. This is all critical, hard data for wall-avoidance.

For fun, I tested the program with a rather aggressive goal, and the program tells me that I may not be able to complete a marathon in two hours: “Your target pace may be too fast for your level of aerobic fitness, putting you at risk of hitting the wall.” I think it nailed that.

Rapoport BI (2010). Metabolic factors limiting performance in marathon runners. PLoS computational biology, 6 (10) PMID: 20975938

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