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Hangry for Brain-Aid : Endurance Athletes and Brain Bonk

We've all hit the wall sometime, crumbling part way through an epic run or ride. There were Hanger issues. It wasn't pretty. Your brain. just. bonked. Why does this melt-down happen during tests of physical endurance?

What is "Hitting the Wall" and why do brains bonk when fuel has fizzled?

When endurance athletes hit the wall it means that the brain has detected dwindling sources of glycogen fuel in the body. It can be a harsh mental prompt that wills you to stop.

The 'Central Governor Theory' given by Tim Noakes explains that … central “fatigue is a protective mechanism [by the brain] to ensure you do not reach those physical limits...”(2).

Our central governor may force us to slow down even if our muscles are capable of maintaining a pace and will allow us to speed up at the end of a grueling workout when we would most expect to be crashing. (3)

J. Mark Davis, Professor of Exercise Science at U of South Carolina says the best strategy for delaying both muscle and Central Nervous System fatigue is eating or drinking carbohydrates in order to blunt "the increase in free fatty acids,” that unleash the serotonin that initiate bonk.

Davis explains: "carbohydrates cannot only delay glycogen depletion, but they also delay central fatigue.”

In addition, brain function in general is highly dependent upon blood glucose, as anyone who tries to calculate mile splits at mile 23 probably knows. …” (4) Nom nom nom.

But, not so fast. Dr. Phil Maffetone, author of "Beat the Bonk" reminds us that hitting the wall is not normal, and he points out that fat-burning efficiency is where to look.

“Bonking is caused by an inability to burn sufficient fat for energy.

This source of sustained, long-term energy and stamina has deteriorated and without it one must rely mostly on sugar and its strict limitation to provide energy.

In the process, one uses up too much of one’s glycogen stores and now the blood sugar becomes too low, depriving not just the muscles but the brain of fuel... Many times, an athlete will bonk because more than one problem exists. “ (5)


Metabolism in sport has been likened to a powerful muscle car speeding along. When it's fuel becomes low, a signal lights up to indicate more fuel is needed soon. If the signal is heeded in time, mechanical shut-down, is prevented.

So too, our brain signals the needs of our mechanical body. Ignoring the signal for fueling increases the intensity of that psychological message. A pit stop becomes unavoidable.

On a race track, stressors that would otherwise zap fuel economy, are narrowed down in favor of reserving fuel for speed. There are certainties like: an obvious end point, regular pit stops, and consistent terrain. ​​

But, when energy is limited by uncontrolled variables, what functions does the brain sacrifice, in order to conserve energy?

The Ultra Sacrifice

In a small, stand-alone study of 12 ultra-marathoners who ran nearly 3,000 miles over 64 days without rest, their ability to withstand extreme stress, but remain 'healthy', was examined. Because of this challenge, were there healthy changes to the brain?

MRIs before, during and many months after the race showed that grey matter temporarily decreases in many regions …[the areas responsible for external monitoring functions, sensory and attention]​​

… Thus, we might conclude that under duress, the brain prioritizes internal functions over sensory intake and attention. (12) Heeding the signal or preventing it, extreme physical stress, results in shrinkage.

Speaking of shrinkage, remember writing college papers? Things were going great, you were in the zone of genius, then suddenly it felt like your brain turned into a pile of unproductive raisins...

So, can racing brains bonk during intellectual ultras?


The brain makes up 2% of body weight, yet,
uses around 20% of the oxygen and calories consumed. (1)

Why does it seem you need more food, when studying something new?

Can an active mind get hangry just from it’s unrelenting inner race-pace?

Would a day-glow electrolyte drink prevent brain bonks, too?


©️2017 Lana Brown.

Reference citings below.

Input from credentialed Human Science researchers & specialists most appreciated.

(1) Tremblay, Sylvie. MSc.. Electrolytes & the Brain. Retrieved from:

(2) Noakes, Timothy D. MB ChB, MD. (Sept 2000). Hyponatremia in Distance Athletes - Pulling the IV on the ‘Dehydration Myth’. The Physician and Sportsmedicine. Vol. 28 - No. 9. Retrieved from journal URL:

(3) Sheard, Erin. (Apr 2010). Can your brain hit the wall? Retrieved from journal URL:

(4) Davis, Mark J., Central Nervous System Fatigue. Retrieved from journal: Latta, Sara (2003). The Wall. URL:

(5) Dr. Maffetone, Phil. (April 30, 2015) Beat the Bonk with your Brain: an exerpt from “The Big Book of Endurance Training and Racing”. Retrieved from URL:

(6) Ferris, Jabr. (July 18, 2012). Does Thinking Really Hard Burn More Calories?. Scientific American. Retrieved from journal URL:

(7) Larsen, Gerald E, et al., (Nov-Dec 1995). Evaluation of a “mental effort” hypothesis for correlations between cortical metabolism and intelligence. Intelligence. Vol. 21, Iss. 3. Retrieved from journal URL:

(8) Messier, Claude. Glucose improvement of memory: a review. European Journal of Pharmacology. Retrieved from journal URL:

(9) Chaput JP, et al., (2008 Sep) Glycemic instability and spontaneous energy intake: association with knowledge-based work. 70(7):797-804. DOI: 10.1097/PSY.0b013e31818426fa. Epub 2008 Aug 25. Retrieved from journal URL:

(10) Raichle, Marcus E and Gusnard, Debra A. Appraising the Brain’a Energy Budget. Retrieved from journal URL:

(11) Ferris, Jabr. (July 18, 2012). Does Thinking Really Hard Burn More Calories?. Scientific American. Retrieved from journal URL:

(12) Lee, Ada of Neuwrite West Blog. (May 28, 2014).Does the brain have an energy budget? Under duress: How the Brian Conserves Energy. Stanford Neurosciences Institute: Ask a Neuroscientist. Retrieved from journal URL: https:

(13) Photo credit:

First published Feb 22/17

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