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均是精品，欢迎下载学习！！！欢迎下载百度文库资源资料均是本人搜集均是精品，欢迎下载学习！！！Wordcount:2421HeatAcclimatizationLawrenceE.Armstrong,Ph.D.DepartmentofSport,Leisure,andExerciseScienceUniversityofConnecticutStorrs,CT06269-1110USASubsequenttorepeatedboutsofexerciseinahotenvironment,thereisamarkedimprovementinthephysiologicresponsesofhealthyhumans.Thisimprovedtolerancetoexerciseinheatisknownasheatacclimatization(HA).Whenaccomplishedinanartificiallycontrolledenvironmentalchamber,thisprocessisknownasheatacclimation.TheprimarybenefitofHAisimprovedexercise-heattolerance,evidentasareductionoftheincidenceorseverityofheatillnesssymptoms,andincreasedworkoutputconcurrentwithreducedcardiovascular,thermal,andmetabolicstrain.HAisspecifictothestressimposedonthehumanbody.Forexample,passiveexposuretoheatinducessomeresponses,notablyanimprovedabilitytodissipateheat.Incontrast,physicaltraininginacool-dryenvironmentresultsinmetabolic,biochemical,hematologic,andcardiovascularadaptations.HAviastrenuousexerciseinducesresponsesattributedtobothpassiveheatexposureandtrainingincoolenvironments.Table1illustratestheserelationships.CompleteHArequiresupto14days,butthesystemsofthebodyadapttoheatexposureatvaryingrates.Theearlyadaptations(initial1-5days)involveanimprovedcontrolofcardiovascularfunction,includingexpandedplasmavolume,reducedheartrate,andautonomicnervoussystemhabituationwhichredirectscardiacoutputtoskincapillarybedsandactivemuscle.Plasmavolumeexpansionresultingfromincreasedplasmaproteinsandincreasedsodiumchlorideretention,rangesfrom+3to+27%,andisaccompaniedbya15-25%decreaseinheartrate.Thisreductionofcardiovascularstrainreducesratingofperceivedexertion,whichisproportionaltocentralcardiorespiratorystress,alsodecreasesduringthefirstfivedaysofexercise-heatexposure.Plasmavolumeexpansionisatemporaryphenomenon,whichdecaysduringthe8thto14thdaysofHA(asdofluid-regulatoryhormoneresponses,seebelow),andthenisreplacedbyalonger-lastingreductioninskinbloodflowthatservestoincreasecentralbloodvolume.Theregulationof
