Bonking is a term used by cyclists to describe a sudden state of extreme fatigue. It is characterized by heavy legs and a significant drop in energy levels, making pedaling feel nearly impossible. 

What is Bonking in Cycling?

Bonking, commonly referred to as "hitting the wall," is a cyclist's worst nightmare. It happens when the body's glycogen stores (its primary energy source) have been depleted during prolonged or intense exercise. 

This depletion results in a significant drop in energy levels, leaving you feeling weak, shaky, and unable to maintain your performance. 

Symptoms of bonking include:

- Extreme fatigue

- Dizziness and even 

- Confusion, which can make it difficult to continue riding.

Bonking typically happens when you do not adequately fuel your body before or during a ride. 

The Main Symptoms of Bonking

Extreme Fatigue

When you "bonk," your body runs out of glycogen, which is the primary fuel source for muscles during exercise. Without glycogen, muscles cannot generate enough energy, leading to an overwhelming sense of exhaustion and significantly reduced power output.

Dizziness and Lightheadedness

Low glycogen levels often coincide with a drop in blood glucose (hypoglycemia). This deprives the brain of its primary energy source, resulting in dizziness, lightheadedness, and even a feeling of detachment or imbalance.

Muscle Weakness

Without glycogen, your muscles struggle to contract efficiently. Your body attempts to shift to fat oxidation for energy, but this process is slower and less effective, resulting in noticeable weakness and a lack of coordination.

Irritability and Confusion

Your brain relies heavily on glucose to function. When blood sugar drops, cognitive abilities are impaired. You may (as I did) experience mood swings, irritability, and difficulty focusing or making decisions. This "brain fog" can make even simple tasks seem daunting.

Rapid Heart Rate

In response to energy depletion, the body activates the sympathetic nervous system to compensate. This leads to an increased heart rate as the cardiovascular system works harder to deliver oxygen and attempts to mobilize fat stores for energy.

Sweating and Cold Skin

Bonking can disrupt your body's ability to regulate temperature. The combination of low blood sugar and stress hormones, such as adrenaline, may cause sweating and clammy skin, often accompanied by chills or a sensation of being cold.

The science behind bonking

Bonking happens when your body runs out of glycogen stores, which are essential sources of energy found in the liver and muscles. Glycogen acts as a quick-access fuel for high-intensity physical activity. Once these stores are depleted, your body switches to fat oxidation, a slower process that cannot meet the immediate energy demands of intense exercise.

As glycogen levels drop, blood glucose levels also decrease significantly, leading to hypoglycemia. The brain, which relies almost solely on glucose for energy, starts to malfunction. 

This can result in cognitive issues such as:

- Confusion

- Irritability, and

- Poor decision-making.

Hormonal changes also occur during bonking, triggering a series of stress responses. The adrenal glands release cortisol and adrenaline to mobilize energy from fat and protein stores. However, this response is often inadequate to sustain the high energy output needed for activities like cycling, which can intensify the symptoms.

Moreover, the body struggles to maintain homeostasis. Reduced energy availability impacts everything from muscle contractions to temperature regulation, resulting in symptoms such as cold sweats and shaking. 

How to Recover

Following the steps below will help you recover efficiently and prevent prolonged fatigue or reduced performance in future rides.

Stop and Rest: As soon as you experience symptoms of a bonk, such as extreme fatigue, dizziness, or mental fog, stop riding immediately. Continuing will only worsen your condition and delay recovery.

Refuel Quickly: Your body is in urgent need of energy, so focus on consuming fast-digesting carbohydrates that can quickly replenish your blood sugar levels. Ideal options include energy gels, bananas, or sports drinks that provide easily absorbed glucose. Aim to consume 20-40 grams of carbs right away.

Hydrate: Dehydration often accompanies a bonk. Drink water or a sports drink with electrolytes to replace lost fluids and essential minerals like sodium and potassium, which are crucial for muscle function and recovery. 

Eat a Balanced Post-Ride Meal: After your immediate refueling, have a meal rich in carbohydrates, protein, and healthy fats. Carbohydrates help restore glycogen stores, protein aids in muscle repair, and fats provide longer-lasting energy. A good example is rice or pasta with lean protein and vegetables.

Rest and Recover: Your body requires time to fully recover, especially after severely depleting glycogen. Aim to rest for at least 24-48 hours before attempting another intense workout, and prioritize sleep to quicken your recovery.

Can You Bonk While Training?

Bonking, or "hitting the wall," can occur during training, particularly during prolonged or intense workouts when energy expenditures surpass fuel intake. This phenomenon is more likely to happen if you start your training with depleted glycogen levels, miss meals, or do not sufficiently refuel throughout the session. To prevent bonking, it is crucial to prioritize proper nutrition and hydration.