AccessibilityforscreenreaderHealthScienceTheheatofhotyogacanbeverygood—butalsoriskyforsomepeopleAddtolistOnmylist(iStock)(Juanmonino/GettyImages/iStockphoto)ByEmilySohnDecember30,2017BrianTracyfirstheardaboutBikramyogain2005,whenagraduatestudentapproachedtheexercisescientistwithanideaforstudyingtheclasses,whichlastfor90minutesinaroomheatedtoabout105degrees.Toinvestigate,Tracytriedit.Morethanadecadelater,theresearcherstillpracticesBikramyogasometimes—andnotalwaysforscience."It'soneofthethingsIdoforexercise,anditmakesmefeelreallygood,"saysTracy,whostudiesneuromuscularphysiologyatColoradoStateUniversityinFortCollins.CaseyMaceFirebaughhadtheoppositereaction.ApublichealthresearcheratCentralWashingtonUniversityinEllensburg,MaceFirebaughhaslongpracticedmore-traditionalformsofyoga.Althoughshegavehotyogaachance,itoftenmadeherfeellightheaded."I'marelativelyfitandactiveperson,"MaceFirebaughsays."ButhotyogamademefeelterriblewhenIdidit."Morethan36millionAmericanspracticeyoga,accordingtoa2016survey.Andalthoughtherearenofirmstatisticsonhowmanydotheirposesinheatedspaces,anecdotalevidencesuggeststhathotyogahasgrowninpopularitysinceitwasintroducedtotheUnitedStatesinthe1970s.ThehealthclaimsFranchisesthatofferhotyogasayitsbenefitsincludestrengtheningtheheart,cleaningouttheveins,cleansingimpuritiesfromthebodyandregulatingmetabolismandtheimmunesystem,andtheyoftensuggestthatthosebenefitsaregreaterthanfromunheatedyoga.Butmoststudieshavebeensmall,shortorlimitedinotherways:relyingonpeople'sperceptions,forinstance,orincludingonlypeoplewhowerehealthytobeginwith.Moststudieslackcontrolgroups,makingithardtodetectorexplaineffects.Overallresearchsuggeststhathotyogaisprobablysafeformostpeopleandmighthelpimprovebalance,strengthandotherhealthmeasures,expertssay.Butrisksexist,particularlyforpeoplewithcertainconditions.Andplentyofquestionsremain."I'mayogaloverbyheart,"MaceFirebaughsays."Butmyskepticalscientificselfsays,'Let'sputsomedataonthis.' "TheprojectthatTracydidwithhisgraduatestudentturnedintooneo