How to Avoid Hitting the Wall in a Marathon

You’ve put in all the time and energy into training for 26.2 miles, yet race day comes, and you hit the wall before getting to the finish. What gives?! 

This post will share nutrition tips to avoid hitting the wall in a marathon and eliminate marathon bonking so you can run the race you prepare for.

woman runner hunched over on knees while running

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As any runner knows, there are several aspects of race day that are out of our control, such as the weather, the people around us, the fuel on the course, if the course runs out of water, etc.

However, we are in charge of our personal nutrition plan and this is something that should be practiced time and time again for a successful race day.

Bonking, or hitting the wall, is what can happen if a person is ill-prepared or the race day nutrition plan doesn’t work.

Just as you practice what to eat before a long run, you also want to spend time practicing your fueling during the run and training your gut for runners belly.

Your gut is a muscle and can be trained to take in appropriate amounts of fuel.

runner lying down on track

Many issues of runners gut and runners stomach are just examples of poor nutrition in and around running.

This long distance runners diet plan can help show what foods to eat and avoid before and during endurance running.

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What is Hitting the Wall or Bonking in a Race?

Before we discuss what to do when you hit the wall, let’s talk about the symptoms of hitting the wall and how to avoid it.

Hitting the wall, a phenomenon known as bonking, is a performance-limiting event that happens when carbohydrate reserves drop or become depleted, usually occurring after mile 20 in a marathon.

Since the body can only store a limited amount of carbohydrates in the liver (75-100 grams) and muscles (300-400 grams), it is necessary to take in exogenous carbohydrates during longer endurance events, such as gels or energy chews for running.

runner opening energy gel for running

Muscle glycogen is the major source of carbohydrates in the body, and the main fuel used during endurance activity.

Once these stores become depleted (typically after 1-2 hours of a marathon), performance decreases, and runners may experience adverse symptoms.

Hitting the wall is as much mental as it is physical. Here are some common symptoms experienced when runners hit the wall.

  • extreme fatigue
  • sudden loss of energy
  • dizziness
  • headaches
  • nausea
  • pain
  • cramping
  • crazy emotions emotions

Reasons For Hitting the Wall in a Marathon

From poor nutrition and hydration to imbalanced electrolytes, here are some key reasons you may hit the wall in a marathon. 

This is why we often practice nutrition and key nutrition tips for marathons and develop a fueling plan for the marathon to avoid bonking!

woman tired after a run

As mentioned in the journal, PLOS Computational Biology, more than 40% of runners who attempt to run a marathon experience severe and performance-limiting depletion of physiologic carbohydrate reserves, and thousands drop out before reaching the finish lines (approximately 1-2% of those who start).

More than 40% of runners who attempt to run a marathon experience severe and performance-limiting depletion of physiologic carbohydrate reserves, and thousands drop out before reaching the finish lines.

Rapoport BI. Metabolic factors limiting performance in marathon runners. PLoS Comput Biol. 2010;6(10):e1000960. Published 2010 Oct 21. doi:10.1371/journal.pcbi.1000960

1. Not taking in carbohydrates before the race

We have plenty of research pointing to carbohydrates as the key to fueling our muscles and bodies for longer activity.

Therefore, they should make up the majority of your meals and snacks, especially before a race.

Read this post for ideas of what to eat before a marathon.

turkey sandwich on white bread

Practice eating or drinking carbohydrates 1-2 hours before your run to give your body time to digest them.

A low carb diet and running isn’t helpful for PR’s, performance or high intensities. Having low blood sugar is not ideal when racing!

A study published in the journal, Frontiers in Sport and Active Living noted that, “high carbohydrate content in the pre-event meal led to a longer time to exhaustion compared to a meal with a low carbohydrate content, or exercising in a fasted state.”

To translate, carb loading before a marathon (eating a diet higher in carbohydrates) the week before the race can also be beneficial for enhancing glycogen stores and promoting lasting energy during your 26.2 mile race.

Load up on that pasta before a race! Don’t make these mistakes and learn what not to eat the night before a long run

2. Dehydration

Being either dehydrated or overhydrated can both lead to adverse outcomes during long endurance events.

Fluid deficits of greater than 2% of body weight can impact and compromise performance and cognitive function, particularly in hot weather.

Severe hypohydration with water deficits of 6-10% has more significant effects, such as decreased cardiac output, sweat production, skin and muscle blood flow and can be very dangerous.

With dehydration, everything in the body works less efficiently, meaning your body won’t be able to digest and absorb carbohydrates effectively, which will impact blood sugar and glycogen stores.

green, purple and red electrolyte drinks

Being overhydrated on the other hand is typically a reflection of overdrinking fluids in excess of sweat and urinary losses, and/or not taking in enough electrolytes, namely sodium.

Overdrinking can lead to hyponatremia (low plasma sodium), which can cause nausea, vomiting, headaches, confusion, respiratory distress, low of consciousness and possibly death if untreated.

Read this post to learn more about electrolytes for runners and how to make your own electrolyte drink.

Check out the ultimate guide to hydration for runners to come up with a hydration plan specific to your needs.

Don’t start the race dehydrated, and make sure you’re taking in sufficient electrolytes with your fluids, especially if your sports nutrition gels or chews don’t have a high concentration of sodium in them.

If you’re a salty sweater, you’ll probably need more electrolytes to stay hydrated. Here’s how you can determine hydration during long runs

male runner hunched over knees in hot sun

3. Depleted Glycogen Stores

This is probably the main cause we think of for bonking. The reason we take carbohydrates in during long endurance events is to prevent muscle glycogen stores from becoming depleted.

Once they are depleted, the body has to turn to converting fat and protein to energy, which is a much longer and less efficient process.

Furthermore, as glycogen stores become depleted, blood glucose becomes a more importance source of carbohydrate fuel, however, it is used almost instantaneously.

Hypoglycemia occurs when liver glucose output can no longer keep up with muscle glucose needs during prolonged exercise, leading to headaches, fatigue, nausea and many of the symptoms listed above.

How do you avoid this? Consider proper carb loading before the race, and focusing on some of the best carb loading meals.

Then, aim for 30-60 grams of carbohydrates per hour. Some runners may even need up to 80-90 grams/hour.

Learn more about half marathon nutrition here. 

When do runners hit the wall?

Typically, it’s after the 2 hour mark or after mile 20 and beyond. This is when glycogen reserves have run out, or poor fueling earlier in the race is catching up with people.

This is often when the gut feels more vulnerable and may have trouble taking in fuel, but this is also when it’s most important to take in carbohydrates. 

Some other factors to consider that may impact energy levels, glycogen levels and may lead to hitting the wall in a marathon:

  • caffeine intake (see tips about coffee vs pre workout before a race)
  • not taking in gels with ample water or fluids
  • having the wrong saturation of sugar (ie hyperosmolar drinks or foods can be upsetting to the stomach)
  • speed and intensity (the faster the pace and intensity, the more likely you are to have runners stomach symptoms)

How to Recover From Hitting the Wall in a Half Marathon or Marathon

Unfortunately, there comes a time when you can’t play catch up. One of the things to remember about bonking nutrition is that we want to stay ahead of it to prevent it.

We take prophylactic measures to prevent marathon bonking and the marathon hit the wall phenomenon. 

This is why we, as sports dietitians, preach to never start a race under-fueled or dehydrated. Recovery is also important AFTER the race for many of these reasons as well.

Here are some suggestions for what to eat after a marathon.

overeasy eggs on breakfast skillet

If your body is constantly trying to play “catch up,” it’s expending a lot of energy doing so rather than optimizing muscle contractions and using fuel. 

As with anything, the bottom line of sports nutrition is practice practice practice. Practice and preparation are the keys to success for long distance running.

However, things you can do to avoid hitting the wall in the first place include:

  • Start the race hydrated and follow your hydration plan 
  • Aim for 30-60 grams of carbohydrates per hour
  • Practice carbohydrate loading in the days leading up to the race.
  • Aim for an adequate pre-run or pre-race snack. See some ideas for what to eat before a long run
  • Minimize fat and fiber before a race.
  • If choosing to take in caffeine, stick to dosing of 3-6 mg/kg of body weight, but like anything else practice! Here are some tips on caffeine before running.


  1. Aandahl MH, Noordhof DA, Tjønna AE, Sandbakk Ø. Effect of Carbohydrate Content in a Pre-event Meal on Endurance Performance-Determining Factors: A Randomized Controlled Crossover-Trial. Front Sports Act Living. 2021;3:664270. Published 2021 May 28. doi:10.3389/fspor.2021.664270
  2. Rapoport BI. Metabolic factors limiting performance in marathon runners. PLoS Comput Biol. 2010;6(10):e1000960. Published 2010 Oct 21. doi:10.1371/journal.pcbi.1000960
  3. Thomas, D. Travis et al. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics. 2016,116:501-528. Published February 23. doi

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