In endurance sports such as road cycling and long-distance running, hitting the wall or the bonk is a condition of sudden fatigue and loss of energy which is caused by the depletion of glycogen stores in the liver and muscles. Milder instances can be remedied by brief rest and the ingestion of food or drinks containing carbohydrates. The condition can usually be avoided by ensuring that glycogen levels are high when the exercise begins, maintaining glucose levels during exercise by eating or drinking carbohydrate-rich substances, or by reducing exercise intensity. Etymology, usage, and synonyms The term bonk for fatigue is presumably derived from the original meaning "to hit", and dates back at least half a century. Its earliest citation in the Oxford English Dictionary is a 1952 article in the Daily Mail. The term is used colloquially as a noun ("hitting the bonk") and as a verb ("to bonk halfway through the race"). The condition is also known to long-distance (marathon) runners, who usually refer to it as "hitting the wall". The British may refer to it as "hunger knock," while "hunger bonk" was used by South African cyclists in the 1960s. It can also be referred to as "blowing up" or a "weak attack". In other languages In German, hitting the wall is known as "der Mann mit dem Hammer" ("the man with the hammer"); the phenomenon is thus likened to a man with the hammer coming after the athlete, catching up, and eventually hitting the athlete, causing a sudden drop in performance. In French, marathoners in particular use "frapper le mur (du marathon)", literally hitting the (marathon) wall, just like in English. One may also hear "avoir un coup de barre" (getting smacked by a bar), which means experiencing sudden, incredible fatigue. This expression is used in a wider set of contexts. Mechanisms Athletes engaged in exercise over a long period of time produce energy via two mechanisms, both facilitated by oxygen: via fat metabolism and via breakdown of glycogen into glucose, followed by glycolysis. How much energy comes from either source depends on the intensity of the exercise. During intense exercise that approaches one's VO2 max, most of the energy comes from glycogen. A typical untrained individual on an average diet is able to store about 380 grams of glycogen, or 1500 kcal, in the body, though much of that amount is spread throughout the muscular system