**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.

Glycogen is a form of glucose that our bodies use as fuel. It is stored in the muscles and liver. Athletes bonk when they deplete their muscle glycogen stores. 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. Carbohydrate loading before an event may also make bonking less likely.