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Titolo:
MYOELECTRIC EVIDENCE OF PERIPHERAL MUSCLE FATIGUE DURING EXERCISE IN SEVERE HYPOXIA - SOME REFERENCES TO M-VASTUS LATERALIS MYOSIN HEAVY-CHAIN COMPOSITION
Autore:
TAYLOR AD; BRONKS R; SMITH P; HUMPHRIES B;
Indirizzi:
SO CROSS UNIV,POB 157 LISMORE NSW 2480 AUSTRALIA
Titolo Testata:
European journal of applied physiology and occupational physiology
fascicolo: 2, volume: 75, anno: 1997,
pagine: 151 - 159
SICI:
0301-5548(1997)75:2<151:MEOPMF>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
FIBER CONDUCTION-VELOCITY; EMG-FREQUENCY-SPECTRUM; SINGLE MOTOR UNITS; SKELETAL-MUSCLE; VOLUNTARY CONTRACTIONS; GLYCOGEN DEPLETION; POWER; ELECTROMYOGRAM; BINDING; TENSION;
Keywords:
HYPOXIA; MUSCLE FATIGUE; ELECTROMYOGRAPHY; CONDUCTION VELOCITY; ELECTROMECHANICAL DELAY;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
43
Recensione:
Indirizzi per estratti:
Citazione:
A.D. Taylor et al., "MYOELECTRIC EVIDENCE OF PERIPHERAL MUSCLE FATIGUE DURING EXERCISE IN SEVERE HYPOXIA - SOME REFERENCES TO M-VASTUS LATERALIS MYOSIN HEAVY-CHAIN COMPOSITION", European journal of applied physiology and occupational physiology, 75(2), 1997, pp. 151-159

Abstract

Integrated electromyography (IEMG) of the m. vastus lateralis was analysed during cycle ergometry in male subjects (n = 8). Two work trialswere conducted, one under normoxia (N), the other under environmentalnormobaric hypoxia (EH in which the oxygen fraction in inspired gas =0.116), each trial lasting 10 min. The absolute power output (180 W) was the same for both trials and was equivalent to 77 (4)% of maximum heart rate in trial N. Maximal voluntary isometric contractions were performed after each trial to assess changes in force, muscle fibre conduction velocity (MFCV), electromechanical delay (EMD), median frequency of EMG (MF) and maximal IEMG (iEMG(max)). Biopy samples of muscle were obtained from the m. vastus medialis before testing. Myosin heavy chain (MHC) differences were determined through sodium dodecyl-polyacrylamide gel electrophoresis followed by densitometric analysis. No differences in submaximal IEMG were observed between EH and N trials during the first minute of work. At the end of both work trials IEMG was significantly elevated compared with starting values, however the IEMG recorded in EH exceeded N values by 15%. At the end of the EH trials the following were observed: a decrease in isometric force, MFCV and MFwith an increase in EMD and the iEMG(max)/force ratio. The iEGM(max) was unchanged. No differences in any of these variables were observed after the N trial. Mean (SD) lactate concentrations following EH and Ntrials were 9.2 (4.4) mmol . l(-1) and 3.5 (1.1) mmol . l(-1), respectively. Results indicate that an increased motor unit recruitment and rate coding was needed in EH to maintain the required power output. The increased motor unit recruitment and rate coding were associated with myoelectric evidence of ''peripheral'' muscle fatigue. Subjects withhigher compositions of type II MHC accumulated more lactate and displayed greater reductions in MF and MFCV during fatigue.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 05/07/20 alle ore 01:12:00