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Reduced muscle activation during exercise related to brain oxygenation and metabolism in humans.
Rasmussen P, Nielsen J, Overgaard M, Krogh-Madsen R, Gjedde A, Secher NH, Petersen NC
J Physiol 2010 Jun 1 588(Pt 11):1985-95

Selected by | Frank Nelson and Kevin Conley, University of Washington, United States of America

Brain over brawn: does 'brain fatigue' limit exercise capacity in thin air? Studies of non-exercising muscle reveal the impact of exercising muscle and hypoxia on the ability of the brain to activate muscle to its exercise potential.


The site of fatigue in exercise is much debated, with the muscle cell {1}, the cardiovascular system {2} and even a 'central governor' in the brain {3} all being suggested as the limiting factor. In a clever series of experiments, Rasmussen and colleagues demonstrated that mind matters to maximal exercise. This finding came from studying how non-exercising muscle responds during intense leg exercise in hypoxia. The impact of hypoxia on the brain was estimated from cerebral oxygenation using blood flow and oxygen measurements. First, they found that voluntary activation of arm muscles was reduced by maximum exercise in the legs. Second, they found that external brain stimulation elicited reduced cortical output and muscle activation during maximal exercise in proportion to the degree of cerebral deoxygenation. Thus, the competing impacts of high levels of exercise and low levels of brain oxygenation appear to lead to brain fatigue and reduced activation which prevent the muscle from reaching its exercise potential. Clearly, the brain can set the limit to what muscles can do when exercising in thin air {4}.

References: {1} Allen et al. Physiol Rev 2008, 88:287-332 [PMID:18195089]. {2} Saltin and Strange, Med Sci Sports Exerc 1992, 24:30-7 [PMID:1548993]. {3} Swart et al. Br J Sports Med 2009, 43:782-8 [PMID:19052141]. {4} Amann and Kayser, High Alt Med Biol 2009, 10:149-64 [PMID:1955529].


Evaluated 7 June 2010