Hitting the wall

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.

Ten minutes is approximately the time that it takes for free fatty acids to sufficiently produce ATP in response to increased demand.

[3] The lack of glycogen causes a low ATP reservoir within the exercising muscle cells.

[6] Amino acids are vital to the purine nucleotide cycle as they are precursors for purines, nucleotides, and nucleosides; as well as branch-chained amino acids are converted into glutamate and aspartate for use in the cycle (see Aspartate and glutamate synthesis).

[4][5] The term bonk for fatigue is presumably derived from the original meaning "to hit", and dates back at least half a century.

One may also hear "avoir un coup de barre" (getting smacked by a bar), which means experiencing sudden, incredible fatigue.

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 and may not be available for any specific type of exercise.