Athletes often “bonk” at the end of endurance races mainly because of glycogen depletion, insufficient energy intake during the effort, inadequate hydration, or starting the race at a pace that is too fast.
Many athletes report this drop in performance during the final kilometers of a race, even after a well structured training cycle. In most cases, this does not happen because of lack of fitness, but because of factors related to race strategy, especially nutrition, hydration and pacing.
What does “bonking” mean in a race?
In endurance sports, “bonking” refers to a sudden drop in performance during a race, usually accompanied by intense fatigue, difficulty maintaining the planned pace and loss of muscular strength.
This phenomenon typically appears in the later stages of a race, even when the athlete has completed a solid training cycle.
In most cases, bonking is not only related to physical conditioning, but also to strategic factors such as nutrition, hydration and pacing.
The main cause of bonking
One of the most common causes is glycogen depletion, which refers to the exhaustion of the body’s carbohydrate stores.
During prolonged exercise, carbohydrates are one of the main sources of energy. When these reserves decrease, the body relies more on fat oxidation, which provides energy at a slower rate.
As a result, the ability to sustain exercise intensity decreases, leading to the sensation commonly described as “bonking”. In long distance events, this phenomenon is also known as “hitting the wall”.
Common mistakes that lead to bonking
Insufficient carbohydrate intake
Many athletes consume less carbohydrate than they actually need during a race. In long duration exercise, current recommendations suggest intakes that can reach 60 to 90 g of carbohydrate per hour, depending on the intensity and duration of the event.
When this energy intake is insufficient, the risk of performance decline increases.
Starting the race too fast
Beginning the race at a pace faster than planned increases glycogen use during the early stages of the effort. This can accelerate fatigue and compromise performance in the final kilometers.
Inadequate hydration
Excessive fluid and electrolyte losses can affect plasma volume, body temperature regulation and cardiovascular efficiency, directly impacting performance.
Nutrition strategy not practiced in training
Nutrition strategies should also be practiced during training. The gastrointestinal system adapts to exercise and to carbohydrate intake during prolonged efforts.
When this strategy is not tested in training sessions, athletes may struggle to consume enough energy during the race.
How to avoid bonking at the end of a race
To reduce the risk of performance decline, it is important to plan carbohydrate intake, maintain a consistent hydration strategy and ensure adequate electrolyte consumption during prolonged efforts. It is also essential to practice the nutrition strategy during long training sessions and control pacing in the early stages of the race. These strategies help preserve energy availability throughout the effort and increase the chances of maintaining performance until the end of the race.
Why can well trained athletes still bonk during a race?
Even with good physical conditioning, performance in endurance events depends on energy availability throughout the exercise. When carbohydrate intake, hydration or pacing are not well managed, the body may face energetic limitations that lead to a decline in performance in the final stages of the race.
Scientific reference
Podlogar T, Wallis GA. New Horizons in Carbohydrate Research and Application for Endurance Athletes. Sports Medicine. 2022.
