Do you remember Cadel Evans’ dramatic crack at Passo Coe on the last climb of the Giro d’Italia 2002? The stage was quite long (222 km) with 5 dolomitic climbs and Evans was wearing the Pink Jersey, the symbol of the leader of the general classification. He was riding brilliantly until 10 km to go and his leading position seemed to be very solid. Then, he started slowing down his pace and was overtaken by many riders. By the end of the stage, he was about 15 minutes away from the best cyclists and lost the Giro and even a place in the final Top Ten. Why did he drop so dramatically? This happened because of the famous “bonk”. Evans admitted he had not eaten properly before and during the race, so he was out of energy in the last climb.
This episode is paradigmatic for the importance of proper nutrition for long lasting cycling events. The bonk is not something related to elite cycling only, but almost every amateur cyclist has experienced it at least once in their life. It happens when a cyclist does not eat enough before and during the bike ride and at a certain point he suddenly feels out of energy and becomes incapable of sustaining even a trivial pace. Moreover, during the bonk, the cyclist experiences a reduced ability of driving the bike properly and this results in an increased risk of a bike crash.
The physiological cause of the bonk relies on the reduction of carbohydrates resources for both the exercising muscles and the central nervous system. In a prolonged exercise such as cycling, the reduction of the muscular glycogen stores becomes critical if it is not counteracted by the ingestion of further carbohydrates through diet. Indeed, it is understood that the muscular glycogen stores become a limiting factor for endurance performances lasting more than 30 minutes. Therefore, it is fundamental to have high carbohydrate meals before and during the race in order to furnish additional energy to the body.
What and how should we eat before and during the race, in order to optimize the performance and to avoid the bonk? At first, it is fundamental to start the race with fully replete glycogen stores. To do this, it is recommended to ingest from 7 to 12 gr. of carbohydrates per kg of body mass in the two days preceding the race. The day of the race the cyclist should ingest from 1 to 4 gr. of carbohydrates per kg 1- 4 hours before the start. It has been suggested to have a low fiber diet (e.g. reduced vegetables and fruit content) in the days preceding the race, in order to avoid gastrointestinal discomfort (e.g. nausea, diarrhea, vomiting) during the effort, related to a delayed gastrointestinal emptying. During the race the athlete needs to take some fast-absorption carbohydrates (e.g. sports drink and/or sports gels) in order to have available glucose rapidly for the exercising muscles, then allowing a sparing of the glycogen stores and to maintain an adequate blood glucose level. It is recommended to take from 60 to 90 gr. of carbohydrates per hour of effort. A lesser dose would not furnish enough energy, whereas a bigger dose would not be fully absorbed in the gastrointestinal tract, potentially causing the above-mentioned side effects.
Another important determinant of fatigue is dehydration, which is related to heat dissipation adaptions occurring during exercise, such as perspiration and sweating. Thus, it is very important to keep a good hydration state during prolonged exercise. The recommendation is not to lose more than the 2% of the body mass during the event, because the performance starts impairing and dehydration could occur above this limit. In order to optimize the fluid intake during a race, it is suggested to simulate the sport event in the days preceding it to have a proper calculation of the fluid loss. Moreover, it is recommended to associate electrolytes with water consumption during the race, so as to avoid electrolyte imbalance.