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Titolo:
The role of motor unit rate modulation versus recruitment in repeated submaximal voluntary contractions performed by control and spinal cord injured subjects
Autore:
Thomas, CK; del Valle, A;
Indirizzi:
Univ Miami, Sch Med, Miami Project Cure Paralysis, Miami, FL 33101 USA Univ Miami Miami FL USA 33101 Project Cure Paralysis, Miami, FL 33101 USA Univ Miami, Sch Med, Dept Neurol Surg, Miami, FL 33101 USA Univ Miami Miami FL USA 33101 Med, Dept Neurol Surg, Miami, FL 33101 USA Univ Miami, Sch Med, Dept Physiol & Biophys, Miami, FL 33101 USA Univ Miami Miami FL USA 33101 Dept Physiol & Biophys, Miami, FL 33101 USA
Titolo Testata:
JOURNAL OF ELECTROMYOGRAPHY AND KINESIOLOGY
fascicolo: 3, volume: 11, anno: 2001,
pagine: 217 - 229
SICI:
1050-6411(200106)11:3<217:TROMUR>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
ISOMETRIC CONTRACTIONS; MUSCLE CONTRACTIONS; FATIGUE; HUMANS; ELECTROMYOGRAM; STIMULATION; ACTIVATION; FREQUENCY; BEHAVIOR; PATTERNS;
Keywords:
peripheral fatigue; central fatigue; triceps brachii; surface EMG; axon branch point failure; unit force;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Clinical Medicine
Citazioni:
42
Recensione:
Indirizzi per estratti:
Indirizzo: Thomas, CK Univ Miami, Sch Med, Miami Project Cure Paralysis, POB 01690 R-48,1600 NW 10th Ave,R-48, Miami, FL 33101 USA Univ Miami POB 01690 R-48,1600 NW 10th Ave,R-48 Miami FL USA 33101
Citazione:
C.K. Thomas e A. del Valle, "The role of motor unit rate modulation versus recruitment in repeated submaximal voluntary contractions performed by control and spinal cord injured subjects", J ELECTROMY, 11(3), 2001, pp. 217-229

Abstract

The relative roles of motor unit firing rate modulation and recruitment were evaluated when individuals with cervical spinal cord injury (SCI) and able-bodied controls performed a brief (6 s), 50% maximal voluntary contraction (50% MVC; target contraction) of triceps brachii every 10 s until it required maximal effort to achieve the target force. Mean (+/- SD) endurance times for SCI and control subjects were 34 +/- 26 and 15 +/-5 min, respectively, at which point significant reductions in maximal triceps force had occurred. Twitch occlusion analysis in controls indicated that force declines resulted largely from peripheral contractile failure. In SCI subjects, triceps surface EMG and motor unit potential amplitude declined in parallel suggesting failure at axon branch points and/or alterations in muscle membraneproperties. The force of low threshold units, measured by spike-triggered averaging, declined in SCI but not control subjects, suggesting that higherthreshold units fatigued in controls. Central fatigue was also obvious after SCI. Mean (+/- SD) MVC motor unit firing rates declined significantly with fatigue for control (24.6 +/-7.1 to 17.3 +/-5.1 Hz), but not: SCI subjects (25.9 +/- 12.7 to 20.1 +/-9.7 Hz). Unit firing rates were unchanged during target contractions for each subject group, but with the MVC rate decreases, units of SCI and control subjects were activated intensely at endurance time (88% and 99% MVC rates, respectively). New unit recruitment also maintained the target contractions although it was limited after SCI because many descending inputs to triceps motoneurons were disrupted. This resulted in sparse EMG, even during MVCs, but allowed the same unit to be recorded throughout. These EMG data showed that both unit recruitment and rate modulation were important for maintaining force during repeated submaximal intermittent contractions of triceps brachii muscles performed by SCI subjects. Similar results were found for control subjects. Muscles weakened by SCI maytherefore provide a useful model in which to directly study motor unit rate modulation and recruitment during weak or strong voluntary contractions. (C) 2001 Elsevier Science Ltd. All rights reserved.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 30/03/20 alle ore 19:37:36