Why Runners Bonk: How to Avoid Hitting the Wall

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It happens to most distance runners at some point. You’ve been running, or cycling, hard, pushing yourself to your limits, when suddenly things take a sharp turn for the worse. Your body feels like it is moving through treacle. Each leg weighs two tonnes. You might even start to hallucinate. Quickly, and very unpleasantly, everything seems to be shutting down. Congratulations. You’ve just hit the wall.

A quick science lesson: when you run, you burn fat and glucose. The human body has an almost limitless supply of fat cells – even those super-lean and lithe athlete bodies. But glucose – which the body breaks down from carbohydrates – is different. Your muscles rip through these supplies fairly quickly, generally “running out” after around an hour and a half or two.

This is why marathoners and long-distance cyclists “carb load” before a big race – to make sure that storage is at capacity – and why they then often take mid-race carbohydrate supplements, in solid, liquid or gel form.

So what happens if you don’t? Well, for some people, the system just collapses. Either your muscle glucose plummets, leaving your brain yelling at your legs to move, and your legs whimpering that they are made of jelly. Or your blood glucose tanks, and your brain becomes a foggy mess. This is the wall. In cycling, the same effect is called bonking, which ironically sounds more “Carry On” film than “give up now”.

You might still get over that finish line, somehow, but it’s not going to be pleasant.

Bonking FAQ

Do other sports get it?

The dreaded wall can happen to any endurance athlete: running, triathlons or long-distance cycling can all involve long, extended steady efforts. Other sports follow different patterns – a football match may last 90 minutes or more, but the players are likely to be covering ground in short, sharp sprints with rests in between, and with opportunities for refuelling drinks, so glycogen depletion is less likely.

How do I avoid hitting the wall?

Good training, good nutrition and good sleep can all help stave off that crash. Prevention is far more effective than cure. If you start feeling faint, light-headed or jelly-legged, the chances are you’ve left it too late. Most athletes will, therefore, follow a strict schedule when racing, taking their carbohydrate gels or drinks at specific times that work for them, in order to keep that glycogen topped up at a decent level.

RECOMMENDED: How to Train for a Marathon

What kind of carbs should I take?

This comes down to personal choice. Some people can’t chew “solid” tablets or jellies while running, or stomach the taste of gels. Others swear by jelly beans or home-made chia seed gels. For most, it’s a question of experimentation – not just with what works for your energy shot, but also what your stomach can tolerate.

Isn’t it all in the head?

Yes and no. While your brain can’t out-think glycogen depletion, it can help you to cope with it – and one study in the British Journal Of Sports Medicine has showed that thinking too much about the wall can actually “bring it on” quicker. So a positive attitude can only help.

Five steps to surviving the wall

The golden rules to follow if you want to run through it

1. Get some carbs on board, as soon as possible

This is not a time to worry about your sugar intake: get that sports drink or gel down you. You may have blown the PB attempt, but those carbs kick in after 10 or 15 minutes so they can still help you get to the finish.

2. Don’t forget water

Dehydration slows the removal of food from your gut into your bloodstream = hello, wall. Don’t go overboard – many races report more issues from people who have overhydrated than underhydated – but take frequent small amounts.

RECOMMENDED: The Best Running Water Bottles

3. Play mind games with yourself

Legs are starting to “go” but your brain is functioning OK? Give it something else to occupy it. Doing maths problems is surprisingly effective – not least because the lack of oxygen to your brain seems to mean adding two and two will take you about a mile.

4. Look up

In the last few miles of any race your form starts to go. Cyclists start to weave, runners hunch. Try to look up, and “run tall”. Look around you, find some distractions. If negative thoughts are winning, try counting in your head. If it’s good enough for Paula Radcliffe…

5. Break it down

The last thing you need to be thinking about right now is the bigger picture. A useful running cliché is “run the mile you are in”. Just get to the end of that one, then the next, then the next. One step at a time, one leg in front of the other. Just keep moving. Sometimes that’s all you can do.

I Fought the Wall, and the Wall Won

Elite athletes hit the wall comparably rarely, partly through a question of simple maths. After all, many of them just aren’t running long enough for it to become an issue – lucky sods. But it certainly does happen.

Olympic spirit

One of the most painful few minutes of “running” you can possibly watch is the final stretches of Switzerland’s Gabriela Andersen-Schiess’ 1984 Olympic marathon. Utterly exhausted, barely able to keep her head up, powered only by sheer bloody-mindedness, she crosses the line and collapses into the arms of the officials. The epitome of the Olympic spirit.

Iron women, jelly legs

It’s 1997, the last few hundred metres of the Ironman World Championship and Sian Welch is just ahead of rival Wendy Ingraham. Barely able to stay on her feet, she sees Ingraham approaching and puts on a tiny burst, before falling to the ground. Ingraham staggers alongside – and they both fall to the floor. 140 miles of swim/bike/run will do that to you. The final yards they literally crawl over the line.

Carrying an elephant

US marathoner Dick Beardsley hit the wall at the 1977 City of Lakes Marathon, with 200 metres to go after running without any fluids, having fasted for five days before. “It felt like an elephant had jumped onto my shoulders and was making me carry it,” he said.

Real-life horror stories from victims of the wall

The ultra runner: Robbie Britton

I always imagined my first DNF (Did Not Finish) would involve being dragged kicking and screaming into the back of an ambulance, crawling along on my hands and knees or passed out on some distant, lonely trail in the pouring rain. In reality, I walked up to a race official at the Ultra-Trail du Mont-Blanc [UTMB], a sadistic 103-mile mountain challenge, and handed over my number with a shrug of the shoulders and an awkward smile. The body was still more than willing, it was the mind that had quit. I have stumbled across Greece, vomiting every 15 minutes for 24 hours, to finish a race. At the UTMB last year, I marched the final 30km convinced that the soles of my feet had detached in a bloody mess and soaked into my socks, but I always knew I would finish. Finishing strong is my forte. But that day my mind was not so keen. It told me the effort was worthless. Normally I would ignore those voices, but they had their day. There is always light at the end of the tunnel, but this time I escaped through a hole in the side. robbiebritton.co.uk

The seasoned expert: Adharanand Finn

Three weeks after a marathon PB, I casually sidled down to Cornwall for the Imerys Trail half marathon – an epic, hilly course. I was going great guns and closing down on third place, when shortly after eight miles something somewhere in my body went pop. It was quite surreal. One second I was skipping through the mud and bursting up the hills, the next I felt light-headed and my legs started to wobble. Each mile got harder and harder until even walking was a struggle. I slipped from 4th place down to 42nd. Those watching didn’t even encourage me to start running again: my face clearly told them it wasn’t going to happen. @adharanand

The experienced runner: Simon Freeman

Aiming for a PB in London a few years ago, I set off at 2:30-something marathon pace, which was more than realistic given my training. It was warm and I didn’t drink. By Canary Wharf, I was so dehydrated I couldn’t swallow or breathe properly and I ended up walking through an aid station in tears. I glugged two bottles of water and half a bottle of Lucozade – I hate that stuff normally – and within a few minutes I was back running again. I hit my pace after a mile, and ran the rest of the way pretty much to plan. The wall was hard to hit, but over quickly. And I learned a lesson. simonfreeman.co.uk

The DNF: Stephanie

I trained really hard for my second marathon. I did everything in my plan and spoke to a coach regularly for tips and advice. But at mile 21, it all went horribly wrong. I still don’t know what exactly happened, it’s all very hazy, but the last thing I remember is my legs just going underneath me – like I was a puppet and someone had cut the strings. I was so out of it they put me in an ambulance and took me to hospital. Apparently when they asked me my name, I said “I don’t know.” I remember almost nothing about it, and I’ve not done a race since, though I still run regularly. It’s just become too scary in my head, this big mental block.

The weird visions: Kate G

It wasn’t strictly a hallucination, but I became utterly convinced I was going to die in last year’s London Marathon. I didn’t know what of, but I ran for about a mile telling myself that I’d better let the next St John Ambulance team know so they could inform my husband of my impending death. I had a gel, a drink and a walk, and then came to, realised what I’d been thinking was more than a bit odd – and made sure I had enough gels for the rest of the race!


Kate Carter is an experienced writer and editor, as well as a dedicated runner. Kate worked at The Guardian for 12 years, establishing and running the successful Running Blog. She contributed to Coach magazine between 2015 and 2016, and has also written for World Athletics, Runners World and Women & Home, among others. Kate has also worked as a presenter on The Running Channel. Kate holds the Guinness World Record for the fastest marathon in a full-body animal costume (female), having run the 2019 London Marathon in 3hr 48min 32sec dressed as a panda.