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What Runners Mean by “Hitting the Wall”
By Alona · Published · 4 min read
Editorial standards and correctionsMarathon preparationmarathon wallmarathon fuelingrunning nutritionglycogenlong-run trainingcarbohydrates for runners
Learn how pace, training, and limited carbohydrate stores can contribute to the marathon wall, plus how to practice fueling safely.
A marathon can feel steady for hours—and then, suddenly, every step feels harder. Runners call this “hitting the wall.” It can seem like the body has switched off, but there is usually more than one reason a runner slows down.
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Today we’ll learn what fuel has to do with the wall, why pace and preparation matter too, and three ways to test your marathon plan during training instead of on race day.
What can contribute to the wall?
Your muscles use different fuels while you run, including carbohydrate and fat. Some carbohydrate is stored in your muscles and liver as glycogen. Those stores are limited. As they fall during a long effort, it can become harder to hold a fast pace.
But low glycogen is not the only possible explanation for a late-race struggle. Starting too fast, inadequate training, hills, heat, illness, and poor sleep can all make a marathon harder.
What research shows
A math-based model of marathon running shows how a runner’s fitness and available fuel affect the pace they can hold. For long events, sports-nutrition experts often recommend taking in carbohydrate during exercise. One established range is about 30 to 60 grams per hour during prolonged exercise; a review of carbohydrate intake and individual tolerance explains why trained athletes in very long events may use more, but that is not a target everyone needs. Stomach tolerance and race conditions matter. More is not automatically better.
A study of more than four million marathon race records defined “hitting the wall” as slowing by at least 25 percent for at least five kilometers. Using that definition, about 34 percent of runners in the dataset hit the wall.
The number depends on how “the wall” is defined, and split times alone cannot tell us why a runner slowed. But it shows this is a measurable pacing pattern—not a single switch that flips at mile 20.
Three steps to practice
- Practice your pace. On long runs, start at a speed that feels controlled. If the first miles feel like a race, slow down. A steady beginning gives you more options later.
- Test familiar fuel. Try a gel, sports drink, banana, or other carbohydrate source you know you can tolerate. Start with a modest plan and practice when to take it. Do not use race day to test a new product.
- Record what happens. After each long run, note the weather, pace, what you ate and drank, and how your stomach and energy felt. Change one part at a time so you can learn what helped.
The lesson is that the marathon wall is not one mysterious switch. Fuel, pace, training, weather, and individual response all matter. Practice your plan in training and adjust it to your own body.
Remember: pace with control, practice your fuel, record what works. Which part of your long-run plan do you want to test next?
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If you’re preparing for the 2027 LA Marathon, join Spark’s 26-week marathon training challenge and practice building a steady routine.
Sources and further reading
- Rapoport, “Metabolic factors limiting performance in marathon runners,” PLOS Computational Biology (2010): research article.
- Smyth, “How recreational marathon runners hit the wall: A large-scale data analysis of late-race pacing collapse in the marathon,” PLOS ONE (2021): analysis of more than four million race records. Its definition of “the wall” is based on pace splits and does not identify the cause of each slowdown.
- Jeukendrup, “A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise,” Sports Medicine (2014): review of intake ranges and individual tolerance.
- Thomas, Erdman, and Burke, “Nutrition and Athletic Performance,” joint position statement (2016): guidance.
About the author
Alona
Alona, I founder and CEO behind Spark (My Founders) and Zai. Welcome. Please reach out if you have any questions or suggestions. We thank you for being here!
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