Document Detail

Human motor unit recruitment and derecruitment during long lasting intermittent contractions.
MedLine Citation:
PMID:  11335149     Owner:  NLM     Status:  MEDLINE    
Seven healthy subjects were investigated in cyclic ramp-and-hold long lasting isometric contractions. Wire branched electrodes were used for selective recording of single motor unit (MU) potentials from m. biceps brachii. MU behaviour was defined in terms of recruitment/derecruitment thresholds (RT and DT) and the duration of interspike intervals (ISI). A total of 63 MUs was investigated: 40 units were active from the beginning of the task performance and another 23 were recruited later. There were no changes in the recruitment pattern of MUs with fatigue development - a short first ISI followed by a very long second one and an almost constant firing rate after this transient phase. The tendency of RT to gradually decrease dominates the results. Thus, the required constant rate of force increase with fatigue development was maintained mostly by the mechanisms of space coding (i.e., decrease of RT and recruitment of additional MUs). Oppositely, the time behaviour of the DT changes was not uniform and rate coding was an essential mechanism in the adaptation of MU activity to muscle fatigue during relaxation phases. The recruitment pattern and fatigue related behaviour of the additionally recruited MUs were similar to those of MUs active from the first cycle of the motor task performance.
P Christova; A Kossev
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology     Volume:  11     ISSN:  1050-6411     ISO Abbreviation:  J Electromyogr Kinesiol     Publication Date:  2001 Jun 
Date Detail:
Created Date:  2001-05-03     Completed Date:  2001-08-02     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9109125     Medline TA:  J Electromyogr Kinesiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  189-96     Citation Subset:  IM    
Institute of Biophysics of Bulgarian Academy of Sciences, Acad. G. Bontchev St. Bl. 21, 1113, Sofia, Bulgaria.
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MeSH Terms
Action Potentials
Isometric Contraction / physiology*
Middle Aged
Motor Neurons / physiology*
Muscle Fatigue / physiology
Muscle, Skeletal / innervation*,  physiology
Recruitment, Neurophysiological*

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