Training to Run a Marathon: What To Do If You Hit The Wall
- Stephanie Ashby
- Dec 29, 2025
- 5 min read
Updated: Dec 30, 2025
You may have heard runners use the expression ‘hitting the wall’ or ‘bonking’ when they describe a feeling of exhaustion they experienced during a long run. But what does hitting the wall actually mean? What is this ‘wall’ and how does it feel when you hit it? Even more importantly, will it happen to you - and what can you do if it does?
Read on to find out.
Hitting the wall is a physiological response that takes place in your body when you run out of glycogen, or fuel.
You see, if you want to run a long distance, like a marathon, there's a problem.
Your body can only store enough glycogen to sustain you for about 20 miles of running. And a marathon is 26.2 miles.
How You Make Fuel to Run
When you exercise, you need fuel to make energy. Simply put, your body breaks down carbohydrates into glucose, and you store the glucose as glycogen in your liver and muscles. It is this glycogen that your body uses for fuel. But you can only store a certain amount of glycogen, and most people will have used it all between 18 and 22 miles.
And that's when you hit the wall.
What Happens When You Hit The Wall
When your brain recognises that you have run out of the best resource it has to keep you running, it switches into survival mode. Finding another way to make the energy you need to keep your body and mind functioning, it starts to use fats and proteins to make fuel.
Unfortunately, your body can’t do this as effectively as it can with glycogen.
In addition, when your body needs to convert fat into fuel, it uses more oxygen. So you will be forced to slow down as your body’s priority is to use the oxygen you’re breathing to make the energy you need.
How it Feels
It can happen fast. One minute you’re running along feeling strong. The next, you are slowing down or walking, every step feels tough, and you’re experiencing extreme fatigue and mental exhaustion.
Symptoms of hitting the wall can include muscle weakness, cramps, nausea, and an overwhelming urge to stop. Mentally, you might feel very negative, experience mental fog, or feel disorientated or detached from your surroundings.
It’s important to note, people have different experiences of hitting the wall. Symptoms can differ and it can happen at different times or distances. Some runners may not hit the wall at all, or at least not during every long run. Most runners who have done more than one marathon say they had a different experience every time.
Contributing factors include:
Your overall diet. It’s better to eat wholefoods when you’re training and maintain a healthy, well-balanced diet so your body gets all the nutrients it needs.
What you eat in the build-up and immediately before you run.
Factors outside your control, for example, the weather, how well you slept, hormones, or your general health or health at the time of your run.
How fast you're running. If you run very slow, your body can use more fat as fuel, so your glycogen stores will last longer.
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 - so that's about 20 miles.
How To Prevent it Happening
Fortunately, there are lots of things you can do to avoid hitting the wall.
Carb load
This is where you consume more carbohydrates a day or two before a long run to ensure your glycogen stores are as high as possible. The same applies to what you eat before you run. Top up on the right foods to give yourself the best chance of sustaining your energy levels for as long as possible.
Pace yourself
Make a plan and stick to it, particularly at the start of a long run, so you don't burn out too quickly.
Fuel During Your Run
Work out a fuelling plan so you consume enough carbohydrates in the early stages of your marathon training run and then throughout. A general rule of thumb is to start taking on fuel within the first 30 minutes of a run, and roughly two gels per hour thereafter.
However, the amount of gels you need depends on the amount of carbs in the products you’re using and a range of other factors personal to you. That’s why it’s essential to try different methods of fuelling during your marathon training.
Training to Run a Marathon With Other Runners
Speaking of marathon training, it will help you to prepare mentally and physically by training with and speaking to other runners. Get tips from runners with experience.
Hydrate
And always remember, drink plenty of water before and during your run, and use electrolytes as part of your race-fuelling plan.
What To Do If You Hit The Wall
If you do hit the wall, don’t give up. There are several things you can do.
Remind yourself that you’re experiencing a physiological response to exercise and it does not mean you cannot carry on!
Be ready for it. If and when the pain comes, don't fight it, embrace it. Think of it as a signal that you're exactly where you're supposed to be. And, you're hurting because you're running at your peak.
Focus on your form. Ask yourself, are you running tall? Are your feet landing underneath your hips? Are your shoulders relaxed and your arms working for you, not against you?
Try to distract yourself. Listen to music - make sure your playlist has tracks that are guaranteed to pump you up. Talk to other runners or try counting in a rhythm.
Positive self-talk, visualisation, and positive mantras can help you get through tough times. As David Goggins, Navy SEAL, says, even when you feel completely wiped out, you are actually only 40% done and you still have 60% left in the tank. Goggins emphasizes that mindset can help individuals push beyond what they perceive as their limits.
It might help to break the remaining distance down in your mind. 10k to go? That's just two park runs, right? Only four laps of the park!
Whatever you do, however slow you go, keep on moving. Every step is taking you nearer to that finish line.
Finally, remember your ‘why?’. You need something powerful enough to pull you forward when your legs are screaming. Write on your arms the names of those you love or for who you are willing to suffer, or listen to pre-recorded messages.
Remember this quote: Run the first 10 miles with your head. The next 10 with your training. And the final 10k with your heart.
Good luck and enjoy your long runs and marathon training! When you cross that finish line, be proud. Less than 1% of people will run a marathon in their lifetime.
Feel free to post any comments or tips for other runners here. And sign up for a long run in and around Coventry with us.
How To Avoid Hitting The Wall On Your Marathon: 6 Expert Tips - Marathon Handbook, 27 April 2022
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