top of page

Guide| Preventing Bonking and Crashing for Triathletes and Cyclists

How to Avoid Bonking or Crashing During Endurance Events
If you are a triathlete or a cyclist endurance athlete, you know how important it is to fuel your body properly before, during, and after your events. Fueling- eating and drinking- is not only essential for optimal performance but also for preventing bonking or crashing, which can ruin your race and your health. "An Ironman's Triathlete’s Bonk Story"

To illustrate how bonking can happen to anyone, and how to learn from it, here is a story from Michael Harvey, a triathlete who bonked at the Ironman World Championship in Kona, Hawaii: I was on track to finish the Ironman World Championship in under 10 hours, until I bonked at mile 20 of the run. I collapsed on the road, dehydrated, hypoglycemic, and heat-stroked.

A volunteer saved me and I was taken to the hospital. I missed the finish line, but I also learned a lot. I learned that bonking is serious and dangerous, that fueling is essential and strategic, and that listening to your body is wise and important.

I also learned that bonking is not a failure, but a challenge and an opportunity. It made me appreciate life, love, and sport more. And it made me want to try again, to prove myself, and to beat the bonk. Avoiding Endurance Disasters: A Guide to Bonking and Crashing What is Bonking?
Bonking is a term for the functional depletion of glycogen, the carbohydrate energy stores by which the body fuels itself . Glycogen is mainly stored in the liver and the muscles, and it can provide energy for up to 90 minutes of moderate to high-intensity exercise. When glycogen runs out, the body has to rely on other sources of energy, such as fat and protein, which are less efficient and slower to metabolize.
Bonking can cause extreme physical weakness, nausea, poor coordination, cognitive impairment, and even muscle loss and immune system damage . Bonking can also affect your mood and motivation, making you feel depressed, irritable, and hopeless. Bonking is not only unpleasant, but also dangerous, as it can increase the risk of injury, dehydration, hypoglycemia, and heat stroke.
For the most part, there are two types of bonking: hypoglycemia (in which your body runs out of fuel, or glucose) and hyponatremia (a loss of key minerals + sodium in the blood). When you hear the word “bonking,” it’s typically the former, but both are terrible fates. Here’s how to distinguish between the two types and what to do about it.
Types of Bonking & Crashes Triathletes & Cyclist Experience 
You only need to experience exercise-induced hypoglycemia once to know it’s bad. Your body—and especially your brain—runs on glucose, and having low blood sugar means your body is out of fuel, often after about two hours of exercise without taking in carbs.
Recognize it: It starts as a headache and can also include nausea, fatigue and a slowed pace. Once you have a hypoglycemia “attack,” it usually takes about a half hour or more to cure—more than enough time to spoil any race or event.
Fix it: When you experience this type of bonk, ingest carbs. Sports drinks and gels are usually readily available, but a sectioned piece of an orange is a revitalizing, pure sugar injection for your system.
Avoid it: Prevention is key. During long exercise sessions, your body needs fuel, period. Gels and drinks are the easiest ways to keep your blood sugar from dropping. Pre-race nutrition is important as well: Make sure you’re getting in the calories your body needs.
Hyponatremia, a loss of sodium in the blood, is common during endurance events, especially those lasting more than four or five hours. The symptoms are often not apparent while they’re happening. When athletes sweat in hot and humid conditions, they lose both water and electrolytes like sodium and potassium.

Read more on dehydration and  heatstrokes .  Recognize it: The symptoms of hyponatremia are different from those of hypoglycemia. The main difference is the changes in mental status that are the hallmarks of hyponatremia: confusion and an inability to focus on where you are. Muscle cramping and swelling of the fingers and toes can also occur.
Fix it: Replace the salt you’ve lost. In the middle of a race, this could mean pretzels, potato chips or other salty snacks—even most sports drinks act as a quickly digestible source of sodium. If hyponatremia gets bad enough, you’ll need a physician-administered saline drip via an IV to bring you back from this bonk. Avoid it: Take in sodium. Prevent hyponatremia by downing sodium in electrolyte drinks and gels instead of water during the race, especially during the second half of your event. As for how much, everyone is different, so go by how you feel, and test it out in training.
What Does Bonking Look Like?
A true bonk is not just a empty lifeless feeling or having tired legs. It’s a total inability to continue, marked by nausea, extreme physical weakness, poor coordination, and a profoundly awful feeling.  Typically, bonking is preceded by waves of progressively worsening symptoms.
Some of the common bonking/crashing symptoms are:
Extreme physical weakness Nausea Poor coordination Shaking hands Dizziness Cognitive impairment Some folks can feel cold
It’s essential to recognize what bonking feels like, not only for your health and safety, because the sooner you realize the problem, the quicker you apply the solution.

How Can Athletes Prevent Bonking?
Bonking can be prevented by consuming adequate and continuous supplies of calories  and electrolytes during long-distance exercise, such as sports drinks, energy bars, fruit, honey, or chocolate milk . Calories are the simplest form of carbohydrate, and they can be quickly absorbed and used by the muscles and the brain. Calories can also spare glycogen, which means that they can extend the time before glycogen depletion occurs .
Triathletes and cyclist endurance athletes need to consume enough calories before, during, and after their events to replenish their glycogen stores and avoid bonking . The recommended calorie intake for endurance athletes varies depending on the duration and intensity of the exercise, but a general guideline is  60 to 120 calories per hour during the event.

These values are based on the assumption that the athlete is consuming mostly carbohydrates , which are the main source of energy for endurance exercise. However, the exact calorie and carbohydrate needs may vary depending on the individual’s body composition, metabolism, and preferences. Therefore, it is important to work with a sports nutritionist or dietitian to determine the optimal fueling plan for each athlete’s needs.
Fueling and hydration strategies should be practiced and fine-tuned during training rides, and followed consistently during races . It is important to find out what works best for you, as different athletes may have different preferences and tolerances for different types of calories and fluids. Some factors to consider are the taste, texture, temperature, concentration, and timing of your fueling and hydration.
If you are looking for some samples of nutrition products to try, you can check out the , a great online platform that offers a curated collection of top brands in nutrition, supplements, and training gear. You can also customize your own box of products based on your sport, goals, and preferences.

Another option is , which makes great custom liquid nutrition and hydration blends tailored to your needs. You can create your own personal performance fuel hydration or protein powder with your choice of flavor, electrolytes, calories, BCAAs, caffeine, and more.
When and Where Do Triathletes and Cyclists Typically Bonk?
Bonking can happen to anyone, regardless of their fitness level or experience. However, some factors can increase the likelihood and severity of bonking, such as:
The duration and intensity of the exercise. Bonking typically occurs during endurance events or long workouts that last more than two hours and require a moderate to high intensity of effort. The longer and harder you go, the more glycogen you use and the faster you deplete your stores.
The environmental conditions. Bonking can be exacerbated by hot, humid, or windy weather, which can increase your sweat rate, fluid loss, and core temperature. These factors can impair your ability to absorb and utilize calories and fluids, and also increase your energy expenditure and perceived exertion.
The nutritional status. Bonking can be influenced by your diet and hydration before, during, and after the exercise. If you start with low glycogen stores, skip breakfast, or eat too little or too late, you are more likely to bonk. If you don’t consume enough calories and fluids during the exercise, or if you consume the wrong types or amounts, you are also more likely to bonk.

If you don’t replenish your glycogen stores after the exercise, you are more likely to bonk in your next session.
Some common scenarios where triathletes and cyclists typically bonk are:
On the bike leg of a long-distance triathlon, such as an Ironman or a half-Ironman. This is because the bike leg is usually the longest and most demanding part of the race, and it requires a steady and high output of power.

Many triathletes underestimate their calorie and fluid needs on the bike, or they forget to eat and drink regularly. They may also experience gastrointestinal issues or cramps that prevent them from consuming enough calories and fluids. By the time they get to the run, they are already bonked or close to it.
On a long and hilly ride , such as a century or a gran fondo. This is because the hills can increase the intensity and variability of the effort, and also the energy expenditure and glycogen use. Many cyclists struggle to maintain a consistent and adequate intake of calories and fluids on the hills, or they overestimate their ability and push too hard.

They may also neglect to eat and drink enough on the flats or the descents, where they should take advantage of the lower intensity and higher speed. By the time they reach the final climb or the finish line, they are bonked or close to it.
On a fast group ride or a race, such as a criterium or a road race. This is because the fast pace and the frequent surges and attacks can create a high and variable demand on the muscles and the glycogen stores.

Many cyclists fail to match their calorie and fluid intake to their energy output, or they have difficulty eating and drinking in the pack or on the move. They may also get dropped or left behind by the faster riders, which can demoralize them and make them bonk mentally as well as physically.
Fueling  is the fast track to success for triathletes and cyclist endurance athletes, as it can prevent bonking or crashing, which can have serious consequences for your health and performance. By consuming enough electrolytes and calories before, during, and after your events, you can ensure that your body has enough glycogen to power your muscles and your brain, and that you can enjoy your sport without suffering. Remember to test and refine your fueling and hydration strategies  during training, and to follow them consistently during races. And don’t forget to have fun!

Guide| Preventing Bonking and Crashing for Triathletes and Cyclists
bottom of page