What Is Hitting The Wall? And How Do You Avoid Hitting The Wall In A Marathon?

‘Hitting the Wall’, or ‘bonking’, can happen to a runner towards the end of a marathon as their body runs out of energy. It can affect all endurance athletes, like long distance triathletes and cyclists. 

While the wall is figurative, it feels painfully real and it’s going to mean that the rest of your race will be a real struggle – physically and mentally. 

But it’s possible to avoid hitting the wall, so follow this guide and you’ll (hopefully!) never hit the wall again. You can jump to the following sections:

• What does hitting the wall or bonking in a marathon mean?
• What’s the science behind why runners hit the wall in a marathon?
• How do you avoid hitting the wall in a marathon?
• How do you deal with hitting the wall if it happens to you in a marathon?
• We also cover the fact that there’s a second wall that you might face in a marathon, and whether you might hit the wall in a half marathon?

WHAT DOES HITTING THE WALL OR BONKING IN A MARATHON MEAN?

The short answer is that our body runs out of its preferred source of energy, and like a car with an empty fuel tank, it no longer wants to go anywhere.

The longer answer is that…

Our body runs primarily on glycogen, which it gets from the carbohydrates that we eat. If we arrive at the start line of a race properly fueled (we’ll explain that, don’t worry), then we carry enough energy in our body to run for 16-22 miles / 26-36km. The trouble, of course, is that a marathon is more than 26 miles / 42km!

So when the glycogen runs out, our body slows down, making every step forward feel so much more challenging. Hitting the wall feels like the road under your feet has turned into wet cement. You feel weak and you can’t think clearly. You begin to doubt whether you can even make it to the finish line. It’s like we hit the wall, then have to drag it along behind us.  

The good news is that we can avoid (or at least delay!) hitting the wall in a marathon. To do that, it helps to understand how and why it happens, so let’s get into the science of energy in the body. 

WHY DO RUNNERS HIT THE WALL IN A MARATHON? 

Glycogen is the favourite fuel for our body, and it’s the easiest source of energy for us to use to power everything we do – and that includes our brain, which uses around 20% of the total glycogen stored in the body. 

When we consume carbohydrates they are converted into glucose, which is then stored as glycogen. We mostly store this glycogen in our muscles, and a small amount in the liver, but much like a car’s petrol tank, we can only store a finite amount of fuel. 

Thankfully, when we run out of glycogen our body doesn’t just shut down, and it can rely on an alternative source of energy: fat. 

We carry a huge amount of potential energy stored as fat (at least enough for a few days). But fat is much harder for the body to convert into energy. The transition from using glycogen as fuel to using fat is the exact moment we hit the wall.  

A large part of why it feels so difficult to carry on running at the same speed when we hit the wall is to do with oxygen. Glycogen doesn’t require much oxygen to convert it into energy, so as our breathing increases during a marathon, most of that oxygen goes towards supporting the muscles, essentially by delivering oxygen to them and removing carbon dioxide. 

Fat requires a lot of oxygen to convert it into energy, so if we run out of glycogen, our body has to reprioritise the oxygen use. Our high breathing rate continues, but we physically slow down because the body has to use oxygen to create energy – it’s essential that the body and brain have energy, but it isn’t essential that we keep on running (even if we really want a PB!). 

For most people, the body’s ‘fuel tank’ of glycogen amounts to around 2,000 calories worth of energy. In a marathon, that means 16-22 miles until the tank is empty. 

Now here’s the important information: if we consume carbohydrates while running, we can keep our essential glycogen stores topped up, meaning we can avoid running out of gas. 

HOW DO YOU AVOID HITTING THE WALL IN A MARATHON? 

To begin, you need to make sure you’ve filled up your tank – in other words, you’ve got to eat enough carbohydrates in the day or two before a marathon (and before your longest runs). This is why you carb load before the marathon as it allows your body to store the carbs as glycogen, which you use as fuel for your runs.

For most people there’s an optimum amount of carbs to consume, but it’s a personal thing you need to figure out for yourself. A general guideline is 5-12g of carbs per kg bodyweight. It’s something you should aim to practise in training to understand what carbs work best for you and how much.

Carb-loading doesn’t necessarily mean eating significantly more calories, instead aim to add an extra portion of carbs to meals (have a piece of toast as well as oats for breakfast), replace some of the protein, fats and fibre you’d eat with carbs (swap the chicken breast for a sweet potato, or choose the garlic bread instead of the side salad), and aim to drink extra carbs in the form of energy drink, or even (non-diet) soda. 

Then you want to be topping up your glycogen stores with a pre-race breakfast with plenty of carbs. 

Even if you get to the start line with a full tank, it’s going to run out before the end of the race. That’s why we need to have energy drinks, gels or chews during the race. Most marathoners should aim to consume 40-80g of carbohydrates per hour that they are running (some elite runners can tolerate 100g per hour, but that’ll be too much for most people). 

Most energy gels have 20g-40g of carbohydrates in them, so that means taking two gels per hour. You can also have an energy drink. 

Taking on gels, chews and energy drinks (or real food if you prefer and can handle eating while running or walking) is something you have to try in training to learn what energy works best for you, and how much you can tolerate. 

And don’t wait until you’re halfway into the run before you start to take on energy. You need to be taking on fuel from early in the race. A good general guide is to take a gel around every 3-4 miles / 5-7km, and have some energy drink. 

If you can take in 150g-250g of carbohydrates during a marathon then you will have enough extra energy to avoid hitting the wall. 

HOW DO YOU DEAL WITH HITTING THE WALL IN A MARATHON IF IT HAPPENS TO YOU?

Sometimes it’s unavoidable that we bonk in a race, especially if we struggle to take on enough calories while running. So if you hit the wall, what can we do about it? 

Unfortunately, it’s not as simple as just consuming more carbs and immediately recovering. It can take hours to replenish the glycogen if we’re severely depleted. 

So if you hit the wall, the only thing you can do is slow down. Even if you want to carry on running at a faster pace, your body won’t respond.   

Focus on your breathing and do your best to consume more energy – drink, gels, chews, whatever you can get – and more water (being dehydrated can also make you feel worse). 

Do your best to stay positive and safe on the course. Just keep on moving forward, even if that means having to slow down or walk. Sometimes we just have a bad day, but we’ll still get to that finish line. 

WATCH OUT: THERE’S A SECOND WALL! 

If the first wall wasn’t scary enough, there’s also a second wall! 

The first one can be avoided by ensuring you carb-load adequately and take on enough extra energy and fluid during your marathon. 

The second wall is more to do with your training. If your body isn’t strong enough, fit enough, or conditioned enough to handle the effort required to run a marathon, then no matter how many gels you take down during the race, your legs are going to struggle. 

The best way to try and avoid this second wall is to do your best to complete your training programme, and especially all the longer runs – doing several long runs of 16-22 miles / 25-35km or up to three hours are essential. If your body is used to running a long way in training, it’s going to feel less difficult in the race. Doing strength work with weights can also help you here. 

There may also be a third wall which is psychological, but that one is likely related to the other two walls. When we struggle from a lack of energy (remember that the brain uses a huge amount of glucose as energy), or we don’t have the fitness or conditioning to carry on, our mind starts to think negatively, and that can then make it feel like we’re having an even harder time. Marathons are a physical activity, but they require a lot of mental strength to keep us going. 

To stay positive, it can help to have a mantra to keep you going. You can think about your reasons why you’re running a marathon. You can try and distract yourself by high-fiving as many people in the crowd as possible, or talking with other runners. 

DO YOU HIT THE WALL IN A HALF MARATHON?

You shouldn’t hit the wall in a half marathon, assuming you’ve gone into the race properly fueled.

The best way to ensure that you don’t hit the wall in a half marathon is to eat a meal which is mostly carbohydrates the evening before the race (pasta, pizza, rice), and then have a breakfast with carbs like oats or a bagel. This will mean your body should have enough stores of glycogen to use as energy. 

You can also top up your glycogen during the race by taking one or two gels, or having an energy drink. Most runners can benefit from doing this. 

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Have you ever hit the wall in a marathon? Do you have any top tips to share?