| Change in muscle fascicle length influences the recruitment and discharge rate of motor units during isometric contractions. | |
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MedLine Citation:
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PMID: 16014788 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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This study examines the effect of fascicle length change on motor-unit recruitment and discharge rate in the human tibialis anterior (TA) during isometric contractions of various intensities. The torque produced during dorsiflexion and the surface and intramuscular electromyograms (EMGs) from the TA were recorded in eight subjects. The behavior of the same motor unit (n = 59) was compared at two ankle joint angles (+10 and -10 degrees around the ankle neutral position). Muscle fascicle length of the TA was measured noninvasively using ultrasonography recordings. When the ankle angle was moved from 10 degrees plantarflexion to 10 degrees dorsiflexion, the torque produced during maximal voluntary contraction (MVC) was significantly reduced [35.2 +/- 3.3 vs. 44.3 +/- 4.2 (SD) Nm; P < 0.001] and the average surface EMG increased (0.47 +/- 0.08 vs. 0.43 +/- 0.06 mV; P < 0.05). At reduced ankle joint angle, muscle fascicle length declined by 12.7% (P < 0.01) at rest and by 18.9% (P < 0.001) during MVC. Motor units were activated at a lower recruitment threshold for short compared with long muscle fascicle length, either when expressed in absolute values (2.1 +/- 2.5 vs. 3.6 +/- 3.7 Nm; P < 0.001) or relative to their respective MVC (5.2 +/- 6.1 vs. 8.8 +/- 9.0%). Higher discharge rate and additional motor-unit recruitment were observed at a given absolute or relative torque when muscle fascicles were shortened. However, the data indicate that increased rate coding was mainly present at low torque level (<10% MVC), when the muscle-tendon complex was compliant, whereas recruitment of additional motor units played a dominant role at higher torque level and decreased compliance (10-35% MVC). Taken together, the results suggest that the central command is modulated by the afferent proprioceptive information during submaximal contractions performed at different muscle fascicle lengths. |
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Authors:
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Benjamin Pasquet; Alain Carpentier; Jacques Duchateau |
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Publication Detail:
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Type: Clinical Trial; Journal Article; Research Support, Non-U.S. Gov't Date: 2005-07-13 |
Journal Detail:
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Title: Journal of neurophysiology Volume: 94 ISSN: 0022-3077 ISO Abbreviation: J. Neurophysiol. Publication Date: 2005 Nov |
Date Detail:
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Created Date: 2005-10-13 Completed Date: 2005-12-02 Revised Date: 2008-11-21 |
Medline Journal Info:
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Nlm Unique ID: 0375404 Medline TA: J Neurophysiol Country: United States |
Other Details:
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Languages: eng Pagination: 3126-33 Citation Subset: IM |
Affiliation:
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Laboratory of Applied Biology, Université Libre de Bruxelles, 28 avenue P. Héger, CP 168, 1000 Brussels, Belgium. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Action Potentials
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physiology* Adaptation, Physiological / physiology Adult Ankle Joint / physiology Differential Threshold / physiology Female Humans Isometric Contraction / physiology* Male Middle Aged Motor Neurons / physiology* Muscle Fibers, Skeletal / physiology* Muscle, Skeletal / physiology* Recruitment, Neurophysiological / physiology* |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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