What is Bonking? And How To Avoid It While Cycling

What is Bonking? And How To Avoid It While Cycling

Have you ever been enjoying a ride until, without much warning, you feel weighed down, without any energy to keep pedaling? This abrupt energy drain is termed “bonking” in the cycling world due to the body depleting its stored glycogen. Replenishing glycogen levels by fueling with a carbohydrate-rich diet is essential, especially for extended or repeated training. Proper fueling before, during, and after exercise ensures optimal performance and safety. In this article, we'll explore the intricacies of bonking–what triggers it, how it manifests, and strategies to prevent it so you can enjoy long, uninterrupted rides.

What is bonking?

Bonking describes feeling completely drained or “hitting a wall” when strenuous exercise depletes the body’s glycogen stores. Muscles require fuel for performance, and cyclists on long rides risk bonking without adequate carbohydrate intake. Bonking can drastically impact your performance, but it can be prevented with proper nutrition for the energy your body expends. 

The science behind bonking

Carbohydrates are the primary energy source during high-intensity (> 60% VO2 max) or prolonged exercise because they are 7% more efficient than energy from fats. When you ingest carbohydrates, your body turns them into glucose, which circulates in the bloodstream. This prompts the pancreas to release insulin, a hormone that transports glucose to your muscle cells for energy. 

The liver and muscles store unused glucose as glycogen. During intense or prolonged exercise, muscle contraction requires a steady energy supply. Stored glycogen is converted into glucose that muscles can use as energy. 

Muscles use up their glycogen stores quickly during strenuous exercise due to a higher demand for glucose and greater insulin efficiency. When the liver runs out of glycogen and cannot replenish glucose to the muscles fast enough, “bonking” occurs. Bonking describes exercise-induced hypoglycemia (EHI), or low blood sugar caused by exercise. When you enter a hypoglycemic state, performance drastically declines, and cognitive function is impaired.

How to prevent bonking

You can prevent EHI or bonking with proper carbohydrate replenishment before, during, and after exercise. Not only is this critical for performance, but it’s also vital for your health. Your muscles are not the only part of your anatomy dependent on glucose. Your brain requires 130g of carbs per day to function. So, eating enough carbs to fuel your brain and the added demands of exercise is essential. 

All physically active individuals, not just cyclists and other athletes, need sufficient carbohydrate intake to maintain daily energy levels. During intense activity, you must strategically refuel to keep blood glucose steady as muscle glycogen depletes.

Many athletes fall short of the recommended carbohydrate intake, and those on low-carb diets often see a notable drop in performance. For instance, one study revealed that race walkers on a low-carb regimen for three weeks did not improve their 10-km race performance. In contrast, race walkers on a high-carb diet boosted their performance by 6.6% in the same period. 

You don’t have to “bonk” to experience a decline in performance. Once muscle glycogen levels drop to 250-300 mmol∙kg-1dry weight or a 40–50% decrease, performance starts to suffer. To recover, you should ingest enough carbs to elevate glycogen levels above 100mmol/kg wet weight and rest for about 4 hours before continuing any intense activity.

Learn more: How to Get Nutrition Right for Before, During, & After Your Rides

What does bonking feel like?

All cyclists who’ve experienced bonking would agree that it stops you in your tracks, making it impossible to press on. Bonking mirrors the symptoms of low blood sugar (hypoglycemia), such as dizziness, shaking, sweating, weakness, and fatigue. These symptoms can make it difficult for you to continue riding and can lead to injuries. If hypoglycemia progresses, weakness sets in, and you may have difficulty seeing and experience confusion or seizures. 

Bonking or fatigue?

Fatigue is much broader, more common, and less debilitating than bonking. It describes a general sensation of tiredness or lack of energy. Fatigue can be both physical and mental and result from various causes, including overtraining, lack of sleep, stress, illness, or psychological factors.

Unlike bonking, fatigue might not have an immediate or single remedy. Addressing it may require a combination of rest, improved nutrition, stress management, or even medical intervention if the cause is an underlying health issue.

Bonking or dehydration?

Both bonking and dehydration impair performance. But bonking occurs when the body runs out of energy quickly, while dehydration happens when the body doesn't have enough water, leading to an imbalance of salts and sugars in the blood. The main symptoms of dehydration include thirst, dry mouth, headache, and dizziness. Severe dehydration can lead to cramping or heat exhaustion. Hydrate with electrolyte-packed hydration drinks to avoid dehydration while cycling and refuel with carbohydrates to prevent bonking.

Although two different things, bonking and dehydration can occur simultaneously, especially since refueling and rehydrating go hand-in-hand. Dehydration decreases blood plasma volume, essential in transporting nutrients like carbohydrates to the muscles. If you get dehydrated, your body won’t be able to replenish glycogen stores fast enough, which could lead to bonking. 

Learn more: The Best Cycling Hydration Drinks

How to recover from bonking

After bonking, it’s essential that you not continue exercising immediately, even if you start to feel better. Rest and replenishment are essential to recovering from bonking. Bonking may interfere with your training, which makes proper fueling before, during, and after rides a must. Here are a few immediate actions to take after bonking on a ride or during any other activity: 

  1. Immediate carbohydrate intake: Consume fast-acting carbohydrates like sports gels, drinks, or sugary foods. These will help raise blood sugar levels quickly.
  1. Hydration: Dehydration can exacerbate the symptoms of bonking. Drink water or sports drinks that contain electrolytes to help restore fluid balance.
  1. Rest: Resting and letting your body recover is crucial. Adequate rest may take a few days, depending on how depleted your glycogen stores are. 
  1. Eat a balanced meal: Once you've stabilized, eat a balanced meal containing carbohydrates, proteins, and fats. This will help replenish glycogen stores and aid recovery.
  1. Evaluate and adjust: After recovering, take some time to evaluate your nutrition and hydration strategies and plan for more frequent or larger carbohydrate intakes on rides.

How to avoid bonking while cycling

Eat enough carbohydrates to match your training load. 

The amount of carbohydrates you need depends on the duration and intensity of your training. For instance, a grueling three-hour mountain ascent demands significantly greater carb intake than a moderately intense one-hour ride. Ensuring that your carbohydrate intake matches your training load provides your muscles with the necessary fuel to perform and prevent bonking.

Pre-fuel and re-fuel adequately. 

Your body's ability to perform and recover is significantly influenced by what you consume before and after a ride. Pre-fueling ensures you start with full glycogen stores, giving you a solid energy base–fueling with carbs 2-3 hours before your ride is ideal. Then, post-ride re-fueling helps restore those depleted energy stores. This habit helps in immediate recovery and prepares you for subsequent rides.

Consume high-GI carbohydrates before and after exercising. 

The Glycemic Index (GI) measures how quickly a food raises blood sugar levels. High-GI carbohydrates, such as white bread, most breakfast cereals, and sugary drinks, provide a rapid energy source. When cycling, especially during longer rides, these carbohydrates can be beneficial as they deliver quick energy, helping to delay the onset of fatigue and preventing bonking.

Replenish carbs within 30–60 minutes after exercising.

The period right after exercise is often termed the "golden window" for recovery. This is when your muscles are most receptive to refueling. Consuming carbohydrates within this time frame ensures that the glycogen stores are replenished efficiently, speeding up overall recovery and reducing the risk of bonking in future sessions.

After a strenuous ride, your muscles are primed to absorb and store carbohydrates efficiently, but this prime state is time-sensitive. If you wait too long post-exercise (beyond that 30-60 minute window), you’ll miss out on this optimal replenishment period, making your recovery less effective. So make the most of your body's natural recovery mechanisms and aim to consume carbohydrates within this critical window.

Between training sessions, consume a high-carb diet. 

Research demonstrates that supercompensation of glycogen stores with a diet consisting of greater than 60% of total calories as carbs or at least enough carbs to offset those burned during rest and training leads to a boost in muscle glycogen stores.

Don’t choose a low-carb diet.

Low-carb diets are not ideal for endurance cyclists. These diets can deplete the glycogen stores more quickly, leading to an earlier onset of fatigue and increasing the risk of bonking. For those who spend extended hours on the saddle, a diet rich in carbohydrates ensures a more sustained energy release, helping to maintain performance throughout the ride.


Bonking underscores the importance of strategic nutrition before, during, and after strenuous activities like cycling. By understanding the body's reliance on carbohydrates as its primary fuel source, you can take proactive measures to prevent this abrupt energy depletion. Bonking is daunting but entirely avoidable with the proper knowledge and preparation. Whether you're a casual rider or an avid cyclist, fueling your body well is key to pushing boundaries and achieving new milestones.

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