Document Detail

Motor units within the normal rat medial gastrocnemius.
MedLine Citation:
PMID:  8329209     Owner:  NLM     Status:  MEDLINE    
The contractile properties, fatiguability and axonal conduction velocity were determined for 118 motor units in the medial gastrocnemius of eighteen rats. Fast-twitch and slow-twitch units could be categorized on the basis of the 'sag' test. For the purposes of statistical comparison the fast-twitch units were classified on the basis of their fatiguability as fast-fatiguable (FF), fast intermediate (FI) and fast fatigue-resistant (FR). As such, FR units tended to have a longer isometric twitch time course than other fast-twitch units. On the basis of peak tetanic force FF units were largest (mean 341 +/- 120 mN) followed by FI (145 +/- 85 mN), FR (87.3 +/- 38) and slow units (40.4 +/- 11.0 mN). There were no differences in motor axonal conduction velocity. Although units were categorized, it is clear that for all characteristics investigated the fast-twitch units exist as a continuum. Some of the largest FF units (peak force 350-500 mN) failed to maintain force with high-frequency stimulation (300 Hz) and this was associated with a failure of the EMG signal.
L J Einsiedel; A R Luff
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Experimental physiology     Volume:  78     ISSN:  0958-0670     ISO Abbreviation:  Exp. Physiol.     Publication Date:  1993 May 
Date Detail:
Created Date:  1993-08-19     Completed Date:  1993-08-19     Revised Date:  2003-11-14    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  371-81     Citation Subset:  IM    
Department of Physiology, Monash University, Clayton, Victoria, Australia.
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MeSH Terms
Electric Stimulation
Motor Neurons / physiology,  ultrastructure*
Muscle Contraction / physiology
Muscles / innervation*,  physiology
Neural Conduction / physiology
Rats, Sprague-Dawley
Time Factors

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