Review ARTICLE

Front. Physiol., 11 April 2012 | doi: 10.3389/fphys.2012.00082

Fatigue is a brain-derived emotion that regulates the exercise behavior to ensure the protection of whole body homeostasis

  • UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Cape Town, South Africa

An influential book written by A. Mosso in the late nineteenth century proposed that fatigue that “at first sight might appear an imperfection of our body, is on the contrary one of its most marvelous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism” so that “muscular fatigue also is at bottom an exhaustion of the nervous system.” It has taken more than a century to confirm Mosso’s idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso’s ideas were supplanted in the English literature by those of A. V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles – “peripheral fatigue” – to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance. This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops. These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop. The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body’s known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance.

Keywords: fatigue, central nervous system, central governor model, anticipation, feedback, feedforward, brain, skeletal muscle

Citation: Noakes TD (2012) Fatigue is a brain-derived emotion that regulates the exercise behavior to ensure the protection of whole body homeostasis. Front. Physio. 3:82. doi: 10.3389/fphys.2012.00082

Received: 19 December 2011; Paper pending published: 09 January 2012;
Accepted: 20 March 2012; Published online: 11 April 2012.

Edited by:

Christina Karatzaferi, University of Thessaly, Greece

Reviewed by:

Henriette Van Praag, National Institutes of Health, USA
Giorgos K. Sakkas, Center for Research and Technology Thessaly, Greece

Copyright: © 2012 Noakes. This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.

*Correspondence: Timothy David Noakes, UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, University of Cape Town, Boundary Road, Newlands, 7700 Cape Town, South Africa. e-mail: timothy.noakes@uct.ac.za

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