Running a marathon is hard—but what can make it truly brutal is “hitting the wall.” If you’ve experienced it, you know there’s no mistaking the feeling.
Hitting the wall happens when your body runs low on available fuel, forcing you to slow down to conserve energy. Suddenly, your legs feel heavy, almost unresponsive, and every step toward the finish line takes far more effort than it should.
Also known as “bonking,” this is one of the most common—and frustrating—experiences in marathons. It’s derailed countless races, turning strong performances into survival mode and costing runners their PRs.
The good news? It’s not inevitable. With the right training, fueling strategy, and pacing, you can avoid the wall and finish your marathon strong.
What causes hitting the wall?
Hitting the wall happens when your body runs out of its most efficient fuel source: glycogen, which is stored in your muscles and liver.
During a marathon, your body primarily relies on glycogen for energy. But these stores are limited—and once they’re depleted, your body is forced to switch to burning fat for fuel.
While fat is a nearly unlimited energy source, it’s much slower and harder to access.
Because your body can’t convert fat into energy quickly enough to maintain your pace, you’re forced to slow down. That sudden drop in available energy is what makes your legs feel heavy, your effort skyrocket, and your pace fall apart.
Runners usually hit the wall around mile 18 or 20 in a marathon, depending on how fast they are running. Glycogen stores last about two hours or up to 2,000 calories. On average, we burn about 100 calories per mile, depending on our pace and weight.
What does hitting the wall in a marathon feel like?
Hitting the wall is both a physical and mental assault. Fatigue comes on hard and fast—your legs feel heavy and unresponsive, like you’re trying to run through quicksand, and every step suddenly takes far more effort than it should.
At the same time, the mental battle ramps up. Negative thoughts creep in, telling you to slow down, stop, or quit altogether.
This response is actually by design. As glycogen stores run low, your brain shifts into self-preservation mode. It increases fatigue signals—partly through changes in brain chemistry, such as elevated serotonin levels—which can reduce muscle activation and amplify feelings of exhaustion.
The result is a powerful combination of physical slowdown and mental resistance, both pushing you to back off the effort.
Related: What’s a good marathon time?
What to do if you hit the wall
First—don’t panic. You can keep going, and while it’s uncomfortable, hitting the wall isn’t dangerous. The key is to stay calm, stay fueled, and shift your focus.
1. Keep fueling, even if you don’t feel like it
Continue taking your gels and sipping electrolytes. Your body still needs fuel, and even small amounts can help stabilize your energy and slow the downward spiral.
2. Narrow your focus
Don’t think about the miles ahead. Just focus on the next step, then the next. Forward progress—no matter how slow—is still progress.
3. Let go of pace goals
This is not the moment to chase splits. Shift your mindset from performance to perseverance. Your only job is to keep moving toward the finish line.
4. Find something positive—anything
When everything feels bad, zoom in on one small thing that doesn’t. Maybe your breathing is steady, your arms feel relaxed, or even just your fingers feel okay. Use that as your anchor.
5. Use distraction to your advantage
Talk to another runner, engage with the crowd, or let your mind wander to something completely unrelated—what you’ll eat after, your grocery list, anything. Studies show that this kind of mental “escape” can help recreational runners push through fatigue.
6. Control your breathing
Tune into your breath and keep it steady and rhythmic. This can help calm your mind and bring your effort back under control.
7. Repeat a mantra
Simple, powerful phrases like “I am strong” or “I keep moving forward” can help override negative thoughts and keep you locked in.
Related: Average Marathon Finish Times
Is it possible to avoid hitting the wall?
Yes! It is possible to avoid hitting the wall. The solution lies in proper fueling, training, and pacing.
Here’s how:
#1: Do a long run every week.
The only way to prepare to run for a long time is to run for a long time repeatedly. Every week of your training, you should be doing a long run.
By running long, your body learns how to store and process glycogen more adequately. By increasing your glycogen stores, you can maintain a pace and delay fatigue. You will also build mental strength, teaching your brain that you can go the distance.
Here are some general rules of thumb for the long run:
- Your long run should be about 30-35 percent of your weekly mileage (more for low mileage runners). So, if you are running 30 miles per week, your long run would be about 9 miles. (Don’t forget deload weeks.)
- Increase your long run week over week by 1-2 miles.
- Do not increase total weekly mileage by more than 10 percent week over week, unless prescribed by a running coach.
- Do most of your long-run miles at an easy, conversational pace to teach your body how to tap into its energy sources, including glycogen and fat.
- If you are aiming for a goal race time, run some of your long runs at your goal marathon pace as a tempo, fast finish, or fartlek to get your body used to running at that speed.
Related: Hitting the Wall: A Survival Guide
#2: Do at least one really long run in your training.
About 2–3 weeks before race day, you’ll want to complete your longest run of the training cycle. This run should prepare you physically and mentally for the marathon—but not be so long that it compromises recovery.
Research and coaching consensus suggest that duration matters more than distance, and that the benefits of long runs begin to plateau after about 2.5 to 3 hours, while fatigue, muscle damage, and injury risk continue to increase.
Because of this, most runners—regardless of pace—should cap their longest run at around 3 hours (or up to ~3:15 max).
General Guidelines Based on Finish Time
- Sub-3:00 runners:
Long runs of 2:30–3:00 hours (often 18–22 miles), sometimes including marathon pace work. - 3:00–4:00 runners:
Long runs of 2:30–3:00 hours, typically covering 16–20 miles. - 4:00+ runners:
Long runs should still be capped at ~3:00–3:15, even if that means not reaching 20 miles. - 5:00+ runners:
Rather than extending to 4+ hours, it’s more effective to cap the long run at ~3 hours and build endurance through:- Back-to-back runs
- Higher weekly volume
- Consistent aerobic training
Why Not Run Longer?
- Glycogen depletion and muscle damage increase sharply after ~3 hours
- Recovery time skyrockets, often interfering with key training weeks
- Injury risk rises, especially for recreational runners
- The aerobic benefits don’t increase proportionally beyond this point
You don’t need to run the full marathon distance in training to be ready for it. In fact, for most runners, capping long runs around 3 hours leads to better consistency, better recovery, and ultimately better race-day performance.
Related: How long should your longest long run be?
#3: Train your gut.
A lot of marathoners bonk in their marathon because they didn’t practice fueling during their long runs. This is a huge mistake. Your gut, like any muscle, can be trained.
To train your gut, you need to take in gels during your long runs to teach it to break down fuel with reduced blood flow (since blood is flowing to your extremities).
Many runners won’t take fuel or perhaps worse, try it on race day, only to get GI distress because their body can’t tolerate the carbohydrates while running.
So, practice your fueling by aiming for a gel (or 30 grams of carbs) every half hour with water. By giving your body glycogen to use while you run, you will preserve your glycogen stores and delay or avoid hitting the wall altogether.
Related: 18 Whole Food Alternatives to Gels
#4: Carb load for days ahead of the race.
Carb-loading isn’t the pasta dinner the night before. That doesn’t give your body enough time to process and store the carbs needed for the race. Carb-loading happens in the days leading up to the race.
- About three days out, start eating 80 to 90 percent more carbs per meal, says registered dietician Kristy Baumann.
- Drink at least 80 ounces of electrolytes and water throughout the day, too.
- Eat a high-carb breakfast the morning of the race and then a snack of some crackers or half a plain bagel about an hour before.
- You can also take a gel at the start line.
This will replenish your glycogen stores, so your body has more fuel readily available as you run.
Related: How to Carb Load
#5: Fuel early and often in the race.
Studies show that those who start fueling early in their marathons have better marathon finish times. So, don’t wait until you start feeling bad to take in fuel (which can be chews, gels, candy, sports drinks, or real food). Start taking them every half hour.1Bennett, J. R., & Kehoe, M. P. (2008). Marathon Fueling Techniques: Physiologic Understanding and a Proposed Intake Schedule. Strength and Conditioning Journal, 30(5), 56–65. https://doi.org/10.1519/ssc.0b013e318187f1b5
- Take a gel (or preferred fuel) at the start line with water.
- Drink electrolyte drinks in between gels.
- Take a gel or fuel every 30 minutes of your marathon with water.
- Don’t skip taking fuel or water, even if you feel like you don’t need it.
Ideally, you will learn which gels or carb sources you tolerate best by practicing your fueling on your long runs.
#6: Pace yourself
The faster you run, the more fuel you burn through. And the faster you run at the start, the less energy you will have for the rest of the race. Remember the old saying, “It’s a marathon, not a sprint.” So, don’t make the rookie runner mistake of going out too fast. Pace yourself!
It is easy to get caught up in the excitement of the crowds or get pulled into someone else’s pace, deluding yourself that maybe you’re fitter than you realized. That is a huge mistake.
Stick to your race plan or the pace you trained for. Run at an easy effort. In the last remaining miles, assuming you’ve taken our advice and avoided hitting the wall, you can give it all you’ve got!
If you need help training for a marathon, check out our marathon training resources:
Wonderful article. Reoriented me towards carbs loading& LSDs
Great article. How exactly can you get your body used to burning fat and not carbs?
More long slow runs!
Excellent Article lots of good information