Bonk
An expression used by cyclists to describe sudden fatigue or loss of energy while exercising. Also known as crashing, blowing up, or running out of steam/gas/fuel, or empty tank. The phenomenon applies to all endurance sports. In running, it may be called hitting the wall. Bonking is distinct from merely being tired due to lack of sleep or from a higher than normal training load. Subjectively, it can be quite unpleasant to bonk! There can be cognitive effects as well as physical ones.
Athletes bonk when they deplete their muscle glycogen stores. Glycogen is a form of glucose (a simple carbohydrate) that our bodies use as fuel. It is stored in the muscles and liver. This can be reversed by eating immediately, preferably foods high in easily-digestible sugars. Water alone will not reverse a bonk. Bonking can be prevented entirely by eating regularly during a race or training, although this is generally not a concern in sessions under 2 hours. Carbohydrate loading before an event may also make bonking less likely. During an event, you can consume carbohydrates in sports drinks, in pre-made energy chews, gels, or bars, or via real food.
