What is cycling bonk? A complete guide and strategy on how to prevent it

July 06, 2022


Photo by Tom Austin on Unsplash

Bonking, also known as hitting the wall, is a term used to describe a cyclist’s exhaustion and reduced performance due to a lack of energy and motivation. It might occur on a long but not necessarily hard ride, during a race, or a fast local group ride where you pushed yourself over a limit. If you have felt like you hit a wall, cannot continue anymore, and reaching your destination seems like an extraordinary effort- congratulations! You officially bonked!

Before continuing with this article, if you just came back from a ride where you might have bonked, stop whatever you are doing and grab a can of coke, a piece of pie, or any product which contains a lot of sugar. Soon I will explain why.


What does bonk mean in cycling?

Bonking is a street name for hypoglycemia - a condition where your blood sugar (glucose) level is lower than the standard range. This happens when the rider is not fueling properly - not restoring glycogen via carbohydrates, which is rapidly depleting during endurance activities. After your body runs out of it, it starts to burn fat which causes extreme fatigue.

A cyclist bonk might happen during training camp, which you have been anticipating for a long time. In one of my articles, I give suggestions on how to ace it, make sure to check it out afterward.

What are bonking symptoms in cycling?

Cycling bonk symptoms vary from person to person, but what most people report are the following:

  • Hunger
    As every cycling enthusiast knows, a feeling of hunger means that it is already too late and you missed a feeding window. Only downhill from there. You cannot stuff your face during a workout, especially during a race, and even if you did, your digestive system would not be able to turn that into fuel quick enough to prevent upcoming bonk.
  • Dizziness or lightheadedness
    Windows of time when you feel like you're out of your body. These are caused by hunger and when your body starts to consume fat to fuel itself.
  • Cramps
    Although it might not only be caused by bonking, but also by neuromuscular fatigue, it is a clear indicator that you are dehydrated and either starting or already bonking.
  • Shiver or similar uncommon reaction of the body
    Shiver is usually linked to your body giving a signal that something is not right. It works like a safety switch and you typically have 2-3 of them. If you start to experience it during a hard workout- you are nearing the edge. Inability to produce any meaningful effort. Even zone 1 or zone 2 feels like a huge struggle, pedaling barely enough to stay rubber side down is the best you can do.
  • The psychological struggle to carry on
    Bonking on a bike comes with a mental burden, such as “Why do I need this?”, “I cannot continue anymore”, etc. This might be the main reason why bonking is so unpleasant. It turns a thing that you love into something you despise.

How to recover from bonking?

Short answer- no, not really. If you didn’t fuel correctly, your only hope is to consume products that are high in sugar, such as gels and energy bars hoping that at this particular time, your body is fast enough to convert these into fuel. But be aware, that this fast sugar creates a threat of cramps. Gels and high-sugar energy bars create an expectation of a high amount of sugar in your body for the remainder of the workout. Once it runs out of sugar and you miss a window to consume more, it breaks down even harder.

Anyways, at this point, your glycogen is way down and you are already burning fat. If you are close to home, pull yourself together and plow through the bonk. If not- try to stop and have some time off the bike, maybe you are on a long-distance ride? If that is the case, try to find a place to grab a decent meal, bonk is rarely reverted by eating energy bars. If you are in a race, time to pull out a broom wagon card, you are done for.

How to avoid bonking in cycling

Bonking when cycling is caused not only by pushing yourself too much on a bike or undernutrition. Not fueling properly beforehand or not replenishing what you burned afterward also play a big part in your future performance. There are 3 stages that you should focus on and I guarantee you will greatly reduce the risk of bonking- before a workout, during training, and after/recovery.

If you experience bonk more often than others, I created a simple sheet example in which you can track your past rides. I suggest cloning it and logging every ride which felt close to the bonk or when you bonked and looking at it the following day to pinpoint what might have caused it. Hopefully, this will speed up the learning process and you will be able to prevent it during future rides.

Take me to bonk sheet

You can clone this sheet into your drive, by clicking on File -> Make a copy.

Most cycling bonks are caused by workouts that are uncommon for an athlete. If you have never cycled 100 kilometers and signed up for a 300-kilometer Gran Fondo, your body is not used to such a load, and no matter how well you fuel before and during, the chances of you experiencing bonk are way up. If that is not the case, let’s pick every stage apart.

Bonking might also be caused by a weak core. If you have been neglecting core strength sessions your lower back, upper back, and abdomen are probably overworked during hard cycling workouts. This causes extreme fatigue and discomfort on the bike, if you would like to avoid that, try these 5 cycling-specific core exercises that can be completed in your living room.

Bonking prevention before a workout

Most endurance athletes have heard of the term carb loading. Carb loading is a process in which you store a lot of carbohydrates before a workout. Although there are different types of it, I will only focus on what I have done in the past and what works for me.

I have also written a short post on cyclists’ breakfast suggestions, if you are out of ideas and not sure what to eat before a ride, give it a read afterward.

  • Carb and electrolytes loading before the hard rides
    Will you be riding a fast ~3 hours group ride which is more taxing than your usual effort? Maybe a race? Even if a new workout with intervals that you have never done before is upcoming, increase carbohydrate consumption 1-2 days before an event and consume electrolytes and whole foods on the day of the event. You will have to find what amount and what food works for you, but don’t go easy on it, better safe than sorry. **Also, adjust based on the weather**. Is it mid-summer and you are sweating like a pig on your big day? Down those pints of electrolytes like crazy, all the surplus will be flushed out of your system, so there is no risk of consuming too much. Remember that you most likely will only be carrying 2 bottles if you don’t have a team/support car following you, so load up beforehand.

There is no need to overdo it, but start to experiment whenever you have a hard day in the saddle coming up. As time goes on, you will learn a thing or two about your own body and how it reacts to different conditions or challenges. Prevention is the best way to fight the cycling bonk and proper nutrition beforehand will definitely help you to reduce your chances of experiencing it.

Bonking prevention during a workout

A general rule of thumb is that to avoid bonking, cyclists should eat in small portions often on a bike. This is a timetable that I follow based on the intensity of a workout and which works for me, by no means it will fit you like a glove, but it might be a good starting point to determine one for yourself.

  • Long easy rides

    Typically 2-4 hours, Zone 2 effort. I consume carbs every 35-40 minutes and avoid gels to prevent myself from bonking. Anything solid and even better- whole food works fine. Examples of such food: dates, bananas, oat biscuits, oat bars with some nuts&chocolate, homemade rice cake (although usually too lazy for that). Reason for avoiding gels- there is no need to consume them and missing a feeding interval on gels might cause cramps due to high sugar levels in the product. If I have a Gran Fondo that extends well over 4 hours, I’d usually look for opportunities to stop and grab a proper lunch, because it is hard to survive 5 or more hours on snacks.

  • Moderate rides

    Typically up to 2 hours, Zone 2- Zone 3 effort, maybe a steady ride with some intervals or a fast group ride. I start to squeeze feeding intervals to 25-35 minutes. During a workout like this efficiency and quick hands are key. You usually have less time to unpack bars, your focus is on following the wheel or maintaining constant effort. Food that I use for such rides: dates (singly packed in foil), energy bars (make sure to tear packaging before training for easy access), and a single banana to not upset the stomach with refined products, such as bars.

  • Hard rides

    2-3.5 hours, typically race-like workouts or proper races. I eat every 20 minutes, food of choice- gels and energy bars with a couple of dates in between. There is no time to unpack or chew something whole, so downing gels are the best bang for the buck. On the other hand, during a couple of years of racing, I noticed that due to high sugar and carbohydrate levels in gels, you might get cramps if you miss a feeding window, so make sure to keep an eye on that.

On top of that, don’t forget to put electrolytes in your drinks. These products restore electrolytes that are lost when sweating and provide carbohydrates to fuel activity. I use Science in Sport GO Electrolyte because the price is acceptable and it tastes better than any other product I tried. Drinking water is only acceptable if you are doing a 1-hour recovery spin, but even on days like this, if you had a hard effort a day before, don’t skip on nutrition. Better safe than sorry.

If you read other articles, people tend to go mental about this and start calculating carbs per hour, reading labels of products in stores like maniacs, and then calculating the exact amounts they need to consume in a given period of time. This only causes faster energy consumption because of the pressure it creates. If you are not a professional athlete or not competing in any ultra bike race, keep it simple. Bonking prevention when cycling comes naturally once you start to push yourself over the edge more often and learn from mistakes you did in the past.

Bonking prevention afterward (recovery)

So you just came back from a super hard or long ride and you didn’t bonk, time to celebrate! Well, not yet. Recently together with Kaunas cycling, a continental cycling team, we created an easy and cheap cycling recovery strategy. I suggest you give it a read, we did go in-depth there.

Back on the topic. Good job on nailing down that nutrition, but you have just dragged your body through an unusual amount of stress and fatigue, you need to help it repair itself. First of all, the glycogen window is real, according to Dr. Gary Huber:

The first 30 minutes after a workout is KEY to your recovery. After working those muscles give the right fuel in the right time frame to optimize recovery and next performance.

Therefore you must consume some fuel even before taking off those bibs. My favorite candidate for a post-workout drink is chocolate milk. Although store-bought stuff works fine, make sure that the one you are buying is in 4:1 carbs to protein ratio. If you feel like whipping your own chocolate milk that will also feed your soul, here is my favorite, borrowed from Harry Sweeny’s, a professional bike rider from Lotto-Soudal, video on pro cyclist nutrition. The recipe is really easy and you can blend it in 2 minutes:

  • 2 frozen bananas
  • 3 tablespoons of Nesquik cacao powder
  • 1 scoop of protein powder
  • A couple of cracks of salt
  • Milk (I like 1.5-2%) to bring it to my preferred consistency

After consuming a well-deserved recovery drink and taking a shower, make sure to restore lost nutrients with a proper meal, once again try to consume more carbs, such as rice or pasta, to prevent sleeping problems, especially if you finished a workout later in the evening. Another tip if your workout was in the evening- try to go for a short walk before hitting the bed, this will help you fall asleep faster by unwinding steadily. If you have cramps during the night, try magnesium tablets and consume more liquids.

Foam rolling works wonders too. Try to follow a 10-15 minute guided workout on youtube which focuses on reducing tense muscles in the legs and tension in the lower back.

If you have a lot of days of cycling in succession, for example participating in the Rapha 500 challenge, you might be interested in my article on it as well, I share the preparation process, gear, and most importantly- stats. If you are interested in numbers, you will like it. Other than that, that’s it! Now you know everything you need to know to prevent bonking when cycling.

Let me know your worst bonk in the comments down below and make sure to check out other articles on BigBonkTour!


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