Some years ago I wrote a blog post about the importance of pacing during long rides. How cycling too hard at the start of an endurance event leads to a feeling of fatigue, light-headedness, tunnel vision, and confusion. In other words, a bonk.
I hear “bonk” being used to describe muscular tiredness. A bonk is more than that. Runners refer to “hitting the wall.” In German, this is known as “Der mann mit dem hammer.” Likening the sudden drop in performance to being hit with a hammer.
A hallmark of bonking is a sudden and overwhelming feeling of running out of energy. This happens when you have exhausted your body’s glycogen stores, leaving you with abnormally low blood glucose levels. Your muscles have run out of glycogen, and your brain has told your body to stop exerting itself.
Your liver converts glucose into glycogen in a process called glycogenesis. Glycogen is stored in the liver and the muscles and is the primary fuel source for endurance athletes,
How can you tell if you are about to bonk? Sadly humans do not come with the equivalent of a “Low battery” warning. You don’t know that Der Mann mit dem hammer is behind you until he hits you. By then, it is too late to do anything about it.
How can you prevent bonking? Carbo-loading before an endurance event is a common practice. This ensures that your initial glycogen levels are maximized. That means consuming complex carbohydrates. Pasta often comes to mind as a complex carbohydrate. peas, beans, whole grains, and vegetables are also sources of complex carbohydrates.
Carbo-loading can ensure that your glycogen tank is full before you start riding. You need to make sure that your glycogen tank is kept topped-up during the event. This means eating regularly during the event. Some people like energy bars for convenience but foods like fruits, nuts, and potato crisps all work just fine.
What to do if you have let your glycogen tank empty completely, and you are bonking? You need to quickly eat some simple carbohydrates that your body can quickly absorb in order to raise your blood glucose levels again. Simple carbohydrates include energy gels (make sure you drink water with these), kaya sandwiches, sugar cubes, or sweets such as jelly beans. Sugary drinks like Coke, Gatorade, and fruit juice are also good sources of simple carbohydrates.
You need to also rest until you, hopefully, recover enough to continue cycling.
It is possible to train your body to convert glucose to glycogen more efficiently. In other words, to improve aerobic performance or the production of energy from chemical reactions that use oxygen. The aerobic energy system is the primary power source for endurance athletes.
Producing energy anaerobically, in other words, without using oxygen, is impossible to sustain for more than one to two minutes.
You may also hear about producing glucose from fat via a process called gluconeogenesis. This appeals to endurance athletes because the human body stores orders of magnitude more fat than glycogen. Being able to convert stored fat into glucose would mean the end of bonking.
The debate between proponents and detractors of Keto diets and being keto-adapted to take advantage of gluconeogenesis is fierce. I won’t enter that debate. You’ll have to research that topic yourself.