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| Research article summary (published 30 May 2002): |
Central fatigue and motor cortical excitability during repeated shortening and lengthening actions.
Full Abstract
A decline in voluntary muscle activation and adaptations in motor cortical excitability contribute to the progressive decline in voluntary force during sustained isometric contractions. However, the neuronal control of muscle activation differs between isometric and dynamic contractions. This study was designed to investigate voluntary activation, motor cortex excitability, and intracortical inhibition during fatiguing concentric and eccentric actions. Eight subjects performed 143 torque motor-controlled, repeated shortening and lengthening actions of the elbow flexor muscles. Transcranial magnetic stimulation (TMS) was applied three times every 20 cycles. Magnetic evoked motor potentials (MEP), duration of the silent period (SP), and the torque increase due to TMS were analyzed. TMS resulted in a small torque increase in unfatigued actions. With repeated actions, voluntary torque dropped rapidly and the amplitude of the TMS-induced twitches increased, especially during repeated lengthening actions. MEP area of biceps brachii and brachioradialis muscles increased during repeated actions to a similar extent during lengthening and shortening fatigue. The duration of biceps and brachioradialis SP did not change with fatigue. Thus, voluntary activation became suboptimal during fatiguing dynamic actions and motor cortex excitability increased without any changes in intracortical inhibition. The apparent dissociation of voluntary activation and motor cortex excitability suggests that the central fatigue observed, especially during lengthening actions, did not result from changes in motor cortex excitability.Copyright 2002 Wiley Periodicals, Inc.
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Author information
Author/s: Löscher, Wolfgang N (WN); Nordlund, Maria M (MM);
Affiliation: Department of Neurology, University Hospital Innsbruck, Leopold Franzens University, Anichstr. 35, A-6020 Innsbruck, Austria. wolfgang.loescher(-atsign-)uibk.ac.at
Journal and publication information
Publication Type: Clinical Trial; Journal Article
Journal: Muscle & nerve (Muscle Nerve), published in United States. (Language: eng)
Reference: 2002-Jun; vol 25 (issue 6) : pp 864-72
Dates: Created 2002/07/12; Completed 2002/08/02; Revised 2004/11/17;
PMID: 12115976, status: MEDLINE (last retrieval date: 11/6/2008)
Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.
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