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First published online on November 10, 2006.
Experimental Physiology (2006)
DOI: 10.1113/expphysiol.2006.035972
© The Physiological Society 2006
A more recent version of this article appeared on March 1, 2007
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Received September 29, 2006
Revised October 19, 2006
Accepted after revision November 9, 2006

Human, Environmental & Exercise [250]

Corticomotor excitability contributes to neuromuscular fatigue following marathon running in man

Emma Z Ross 1*, Natalie Middleton 1, Rob Shave 1, Keith George 2, Alexander Nowicky 1

1 Brunel University
2 Liverpool John Moores University

* To whom correspondence should be addressed. E-mail: emma.ross{at}brunel.ac.uk.


  Abstract
It is unknown whether changes in corticomotor excitability follow prolonged exercise in healthy humans. Furthermore the role of supraspinal fatigue in decrements of force production and voluntary activation following prolonged exercise has not been established. This study investigated peripheral and central fatigue after a marathon (42.2 km) on a treadmill. Isometric ankle dorsiflexion force and electromyographic responses of the tibialis anterior in response to magnetic stimulation of the peroneal nerve (PNMS), and the motor cortex (TMS) were measured before, immediately, 4 h and 24 h post marathon (MAR) in 9 volunteers (mean completion time, 208 ± 22 min [mean ± SD]). Maximal voluntary contraction (MVC) decreased by 18 ± 7% after MAR (P = 0.009), and remained significantly decreased after 4 h. Amplitude of the evoked response to TMS, but not to PNMS, was depressed immediately post MAR by 57 ± 25% (P = 0.04). Potentiated resting twitch force was reduced in response to both TMS and PNMS post MAR (71 ± 8% and 35 ± 2% decrease, P = 0.035 and 0.037, respectively) and voluntary activation was reduced to 61.9 ± 18% immediately post MAR (P<0.05). All measures had returned to baseline values after 24 h. These results suggest that fatigue was attributable to both a disturbance of the contractile apparatus within the muscle, and submaximal output from the motor cortex.

Key Words: Exercise, Skeletal muscle, Transcranial stimulation




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