Marathon runners know this feeling very well. Non-marathon runners will never know.  When you hit your wall, it's a feeling you'll never forget.


Hitting Your Wall

By Edmund Arellano

NEO Wall5To be fair, not everyone who runs a marathon will hit a wall. There are a number of factors that contribute to this running phenomenon, some of which runners will swear on.  This includes eating a certain diet, or training a certain way. But as the old saying goes, what works for some may not work for all.

But, still. What it is and how do you decrease your chances of hitting this "wall"?

What is it?

The term is used in the running community to describe the moment your body suddenly loses all it's energy and is hit by a wave of fatigue. Most marathon runners will hit this point at around the 20-mile mark and describe it as the moment your legs just want to quit on you. Why the 20-mile mark? There's an interesting theory behind this (discussed later)!


During a long run, your body uses two types of fuel for energy: carbohydrates and fat.  The body relies on carbohydrates for most of its energy and will deplete this source first.  Most of it comes from glycogen stored in the liver and leg muscles. Once your body uses all of its glycogen it starts burning fat. When that happens, your body builds up a byproduct of fat metabolism called Ketones, which causes pain and fatigue.

The Study

Statistically speaking, around 40 percent of marathon runners will hit this figurative wall and about 1-2% will drop out completely (Bradt & Trafton, 2010).

NEO WallIn 2010, an M.D./Ph.D student of the Harvard-MIT Division of Health Sciences and Technology, Dr. Benjamin Rapoport, developed a model which predicted the fuel efficiency of marathon runners. His model allowed runners to calculate how much carbohydrate was needed to fuel themselves through 26.2 miles and at what pace they can reasonably expect to sustain.

Believe it or not, this phenomenon largely has to do with your level of VO2max... oh boy, more confusing running stuff.  But it's actually not that confusing.  VO2max, put simply, is the amount of oxygen your body can transport to the muscles and consume during an aerobic exercise.  Oxygen is important to runners, because it's the only way glucose can be broken down.

Okay, so what level of VO2max should you attain to do well on a marathon?  Most average untrained males have about 45 ml/kg/min of VO2max.  By comparison, an elite marathoner has about 75 ml/kg/min of VO2max.  In other words, work on boosting your VO2max.  A good range would be between 50-60 ml/kg/min.

How do you keep up with this energy?

One word: calories.  Steve Bradt and Anne Trafton (2010) says it best:

A runner with a VO2max of 50 ml/kg/min who wanted to achieve the 3:10 Boston Marathon qualifying time would need to consume 30 calories of carbohydrate per kilogram of body weight (about 2,090 calories for a 154-pound runner), assuming that his legs make up at least 15 percent of his body mass.

Back to the 20-mile theory (stated at the start of this article).  So, why do most marathon runners crash at about the 20-mile mark? Because that's about the time you deplete your stored glycogen calories.  On the average, you burn about 100 calories per mile.  That's an average 2,000 calories burned at 20 miles.  This obviously depends on the gender and weight of the runner, as well as the terrain of the course.

Long story short (Summary)

Work on increasing your VO2max through high speed endurance workouts, and eat more calories.  Don't be afraid to eat DURING your runs also.


Bradt, S. & Trafton, A. (2010). Fuel Efficiency for Marathon Runners. Harvard Gazette. 21 October 2010. Retrieved from: