endurance Endurance (also related to sufferance, resilience, constitution, fortitude, and hardiness) is the ability of an organism to exert itself and remain active for a long period of time, as well as its ability to resist, withstand, recover from an ...

sports such as road cycling and

long-distance running Long-distance running, or endurance running, is a form of continuous running over distances of at least . Physiologically, it is largely aerobic in nature and requires stamina as well as mental strength. Within endurance running comes two d ...

, hitting the wall or the bonk is a condition of sudden

fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

and loss of energy which is caused by the depletion of

glycogen Glycogen is a multibranched polysaccharide of glucose that serves as a form of energy storage in animals, fungi, and bacteria. The polysaccharide structure represents the main storage form of glucose in the body. Glycogen functions as one of ...

stores in the

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it i ...

and

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

s. Milder instances can be remedied by brief rest and the ingestion of food or drinks containing

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...

s. 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

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 The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a c ...

'' is a 1952 article in the ''

Daily Mail The ''Daily Mail'' is a British daily middle-market tabloid newspaper and news websitePeter Wilb"Paul Dacre of the Daily Mail: The man who hates liberal Britain", ''New Statesman'', 19 December 2013 (online version: 2 January 2014) publish ...

.'' 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 The marathon is a long-distance foot race with a distance of , usually run as a road race, but the distance can be covered on trail routes. The marathon can be completed by running or with a run/walk strategy. There are also wheelchair div ...

) 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

German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

, 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 French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...

, 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 Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown or storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membranes. In ani ...

and * via breakdown of glycogen into

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...

, followed by

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

. 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 The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of o ...

, 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. Intense cycling or running can easily consume 600–800 or more kcal per hour. Unless glycogen stores are replenished during exercise, glycogen stores in such an individual will be depleted after less than 2 hours of continuous cycling or 15 miles (24 km) of running. Training and

carbohydrate loading Carbohydrate loading, commonly referred to as carb-loading, or carbo-loading, is a strategy used by endurance athletes, such as marathoners and triathletes, to maximize the storage of glycogen (or energy) in the muscles and liver. Carbohydrate l ...

can raise these reserves as high as 880 g (3600 kcal), correspondingly raising the potential for uninterrupted exercise.

Effects

In one study of five male subjects, "reduction in preexercise muscle glycogen from 59.1 to 17.1 µmol × g⁻¹ (n = 3) was associated with a 14% reduction in maximum power output but no change in maximum O₂ intake; at any given power output O₂ intake, heart rate, and ventilation (VE) were significantly higher, CO₂ output (V_CO₂) was similar, and the respiratory exchange ratio was lower during glycogen depletion compared with control."

Avoidance

There are several approaches to prevent glycogen depletion: *

Carbohydrate loading Carbohydrate loading, commonly referred to as carb-loading, or carbo-loading, is a strategy used by endurance athletes, such as marathoners and triathletes, to maximize the storage of glycogen (or energy) in the muscles and liver. Carbohydrate l ...

is used to ensure that the initial glycogen levels are maximized, thus prolonging the exercise. This technique amounts to increasing complex carbohydrate intake during the last few days before the event. * Consuming food or drinks containing carbohydrates during the exercise. This is an absolute must for very long distances; it is estimated that

Tour de France The Tour de France () is an annual men's multiple-stage bicycle race primarily held in France, while also occasionally passing through nearby countries. Like the other Grand Tours (the Giro d'Italia and the Vuelta a España), it consists ...

competitors receive up to 50% of their daily caloric intake from on-the-bike supplements. * Lowering the intensity of the exercise to the so-called 'fat max' level ( aerobic threshold or "AeT") will lower the fraction of the energy that comes from glycogen as well as the amount of energy burned per unit of time.

References