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Central and Peripheral Fatigue During Passive and Exercise-Induced Hyperthermia.
MedLine Citation:
PMID:  21364487     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
PURPOSE:: Hyperthermia was induced during prolonged exercise (ExH) and passive heating (PaH) to isolate the influence of exercise on neuromuscular function during a maximal voluntary isometric contraction (MVC) of the quadriceps under heat stress. The influence of cardiovascular strain in limiting endurance performance in the heatwas also examined. METHODSCOLON;: On separate days,eightmales cycled to exhaustionat 60% maximal oxygen uptake, or were immersed in a water bath (~41°C)until rectal temperature (Tre) increased to 39.5°C.The ExH and PaH interventions were performed in ambient conditions of38°C and 60% relative humidity with Trereaching 39.8°C during exercise. Prior to (control) and following each intervention,voluntary activation and force production capacity were evaluated by superimposing an electrically stimulated tetanusduring a 45 s MVC. RESULTSCOLON;: Force production decreased immediately after PaH and ExH compared with control, with the magnitude of decline being more pronounced after ExH (P < 0.01).Mean voluntary activation was also significantly depressed following both interventions (P < 0.01 vs. control). However, the extent of decline in voluntary activation was maintained at ~90%duringboth PaH and ExH MVCs.This decline accounted for 41.5% (PaH) and 33.1% (ExH)of the decrease in force production.In addition, exhaustion coincided with a marked increase in heart rate (~96% of maximum), and a decline in stroke volume (25%) and mean arterial pressure (10%) (P < 0.05) CONCLUSIONCOLON;: The loss of force production capacity during hyperthermia originated from central and peripheral fatigue factors, with the combination of heat stress and prior contractile activity exacerbating the rate of decline.Thus, theobserved significant rise in thermal strain in ExH and PaH impaired neuromuscular function and was associated with an exercise performance limiting increase in cardiovascular strain.
Authors:
Julien D Périard; Corinne Caillaudand Martin W Thompson
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-2-28
Journal Detail:
Title:  Medicine and science in sports and exercise     Volume:  -     ISSN:  1530-0315     ISO Abbreviation:  -     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2011-3-2     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8005433     Medline TA:  Med Sci Sports Exerc     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Discipline of Exercise and Sport Science, Faculty of Health Sciences, University of Sydney, Lidcombe, Australia.
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