The Science of Hitting the Wall

We’ve all heard about it, many of us have seen it happen on race day and we might have even experienced it at one point. Whether you call it boinking, tapping out or hitting the wall it’s something most athletes are aware of. I feel like it has happened to me years ago on the bike in the woods but I’m not totally sure. I have talked to enough people though to know it’s a real thing plus I did take a (painfully) comprehensive metabolism course way back so I do know that hitting the wall is a real thing. So let’s bring on the science!

Just a note: This is something I know quite a bit about as a cell and molecular biologist so you might see a few less references than normal in this one.

What does it mean to hit the wall?

Hitting the wall refers to a state of sudden extreme fatigue which actually can get dangerous pretty quickly. It’s closely associated with a higher than previous perceived effort with diminishing performance. That I feel like I’ve definitely experienced a few times. It can also be associated with mental anguish especially during a long race. The idea is you’ve been ticking a long well and all of a sudden you feel as if you just can’t keep going and you’re going to fail. It doesn’t sound like THAT big of a deal but some describe going forward from that point was literally the hardest thing they have ever done.

For some athletes who are not as well trained or fueling their workouts hitting the wall cam become more dangerous. The mental fog can escalate to something more similar to a fuge state where you’re not really in control of your decisions anymore. You could be hella confused, have marked personality changes and that can obviously put you in a dangerous situation. When this happens during a marathon you might see people weep, get very upset or start to look glazed over or dazed.

I’ve definitely experienced the diminishing returns thing when my long runs start to get longer. At this point fueling workouts started to seem a lot more reasonable. For me it happens at about an hour and 20 minuets or so. Once on my bike I think I experienced a more intense version of this. The idea of peddling my bike at any speed all of a sudden seemed impossible and I had some of that mental fog too. I was in the woods at the time but I could see how feeling like this could make you do something stupid like miss a step and fall or not paying the attention you should near traffic.


The biology of hitting the wall

No matter what sport you’re doing you are contracting your muscles to do so. All muscles from your legs to your heart use a substance called ATP (adenosine triphosphate) to accomplish that. Even if you’ve avoided biological sciences you probably still remember that from high school. For most of what we do there is a plentiful supply of ATP on hand. When we start to do endurance events that supply can run short. It doesn’t run out completely otherwise you’d die but as one supply runs short your body starts to get ATP from different metabolism sources. 

First you use glucose (sugar) in the blood which you start to run down in a matter of minuets and then you move on to a very small store of glycogen stored in the muscles. This runs low almost as fast but you have a lot more stored in your liver which can be liberated fast and easily. This supply along with the others is what fuels most of your average run of the mill workouts and is usually enough. Now it does very from person to person depending on factors like how well trained you are, what you ate recently and genetics but this supply does start to run low at about an hour of intense physical activity too. At that point your start liberating energy from fat tissues (using a different metabolic pathway) to get ATP to those muscles. This change in metabolism is what’s associated with that hitting the wall feeling (Rapoport, 2010).

The pretty well established theory is that when fatty acid metabolism takes over that bonking feeling starts. So it’s inevitable that it’s going to happen right? After all you can’t fight biology right? Well no actually there are a ton of things you can do to minimize the effects of hitting the wall some of them you might be doing in training without even realizing it. Others are as simple as knowing about the possibility in the first place. So there you go! A note along the way… this doesn’t mean that you have to exercise hard for over an hour to burn any fat. It really tuns out that a calorie is a calorie after all when it comes to exercise too. Even if you only go for a shorter time and liberate glycogen from your liver during your sweat session that will be replaced from your diet or from fat after the fact. So don’t think you have to hit the wall ever to lose fat from exercise!

 How to avoid hitting the wall

Hitting the wall in marathons is really well established and well studied. So a lot of what we know comes from there. One of the best and easiest ways to prepare for that transition to fat metabolism is to practice it gently. In a lot of ways that’s what your weekly long run is all about! Any long slow workout that you do in training for your sport will gently transition you to primarily fat metabolism over and over again. It turns out your body can actually get better at this over time and you’ll feel less of the effects. I know that in training those first few really long runs each season really break me and feel like crap towards the end. But as I get closer to race day and those runs have added up in number and distance I start to feel like I could literally run like that forever. That’s probably because my body has gotten better at switching to fatty acid metabolism and it’s just no big deal anymore.

The second option is to add fuel to the system as you go. This is thought to make the transition easier as it replenishes your blood glucose levels as you go. In theory this makes the transition to fatty acid metabolism less abrupt and more comfortable. You can do that by a number of methods (which you can read  A LOT about here) like energy gels, drinks and some other options. Your aim is to focus on taking in simple available carbohydrates (often sugars). Obviously the goal of this is to make more ATP but simple carbs are usually well digested and not as likely as protein or fat laden foods to cause stomach upset. But if something works well for you then that’s all that really matters.

Carb loading won’t really help too much with how intensely you hit the wall but it might delay that terrible feeling. It does take some time to move sugar in the blood to the liver and then on to fat. If you happen to load you body in that time with carbs then you will have more on board for your workout. This could make a difference if you run a 10k or maybe even a half in say a bit over an hour and 15 minutes. That ‘extra’ on board can keep you going just that little bit longer and avoid the switch and finish your race. Once again having eaten a lot of carbs in the lead up can also keep your stomach happy too.

One really cool emerging trend in the research is the fact that running at a constant speed is the most efficient way to use your carbohydrate reserves (Rapoport, 2010). This study proves that if a runner has slow and fast intervals they burn more during ‘fast’ intervals than they save during ‘slow’ intervals. Yet another reason to avoid going out too fast! One study even put a finer point on it concluding that if runners during a marathon ran any 1 km 11% slower than the average of the remaining distance they were significantly more likely to report that they had hit the wall during the race (Doherty et al., 2020).

What to do if you bonk

Hitting the wall isn’t fully understood and it happens to about 16% of runners during a marathon (Wolff et al.2018). Those same researchers found that the effects like tremendous fatigue, wanting to give up and shifting thoughts to survival were diminished when participants used certain cognitive strategies to get through the race. This included “if and then” strategies. For example saying to yourself “if I get through this mile there is less than 4 miles left”. Coinsidently I actually use this strategy on long runs breaking each km down to a percentage of the run. So I find myself thinking things like “At the end of this km you will be 90% done.” These strategies worked better than those that focus on distraction when pushing through pain (Raglin, 2007).

Probably the best thing you can do is to develop and implement an effective fueling strategy. Athletes that fuel their endurance activities are less likely to hit the wall in the first place and report less intense negative feelings if they do. I’ve already written a whole lot on the science of that topic so check that out here if you like. While it might seem weird or icky to eat on the run once you find something that works for you it’s literally a game changer for long periods of exertion.

Other stuff I learned about hitting the wall

  • Mathematically speaking it is most likely that you will bonk around mile 21 of a marathon (Rapoport, 2010).
  • If you get to km 33 you are way less likely to experience the wall. (Doherty et al., 2020).
  • Men are more likely to bonk in an event than women ( Doherty et al., 2020).

Have you ever hit the wall? What did it feel like? Were you able to push through and finish your race? What did you learn today? Leave it in the comments below!

Read what I read

Doherty et al. 2020. Devising a Pace-Based Definition for “The Wall”: An Observational Analysis of Marathoners’ Subjective Experiences of Fatigue. Journal of athletic training.

Raglin, 2007. The psychology of the marathoner: of one mind and many. The journal of sports medicine.

Rapoport. 2010. Metabolic Factors Limiting Performance in Marathon Runners. PLOS computational biology.

Wolff et al., 2018. Increase in prefrontal cortex oxygenation during static muscular endurance performance is modulated by self-regulation strategies. Scientific reports.

3 thoughts on “The Science of Hitting the Wall

Add yours

  1. Not directly related to this specific post, but thanks for these informative and science based posts. I’ve been learning a lot from you!


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