ThisistheVOASpecialEnglishEducationReport. 　　Toomucheating.Toomanyunhealthyfoods.Toomanyadvertisementsforfood.Toolittleactivity. 　　DifferentexplanationsareofferedforAmerica'sweightproblem体重问题--aproblemincreasinglysharedbyothercountries.Almostone-fifthofAmericanchildrenandteenagersareoverweight. 　　Schoolshavebeenurgedtoincreasephysicaleducation,animportanttoolforpublichealth.Andmanyhave.Yetnowcomesastudyshowinganincreaseinthenumberofinjuriesin"physed"class.Injuriesincreasedonehundredfiftypercentbetweennineteenninety-sevenandtwothousandseven. 　　Thestudyinvolvedinjuriestreatedinhospitalemergencydepartments急症室.Onlytwopercentwereserious. 　　Theresearchersdidnottrytoidentifythecausesoftheincrease,buttheyhavesometheories. 　　LaraMcKenziefromOhioStateUniversity俄亥俄州立大学wastheleadresearcher.Shesaysonepossibilityisadecreaseinthenumberofschoolnursesduringtheperiodtheystudied.Forexample,atwothousandfourstudyshowedthatthenumberofschoolnursesnationallyfailedtomeetfederalguidelines. 　　Schoolswithoutanurseondutymaybemorelikelytosendaninjuredchildtoahospital. 　　Anotherpossiblereasonformoreinjuriesisachangeinthetraditionalideaofphysicaleducation.This"NewP.E."expandsthekindsofsportsthataretaught.Butactivitiesthatsomeschoolsoffernow,likerockclimbingwallsandskateboarding,canalsoexpandtherisks,saysCherylRichardson.SheiswiththeNationalAssociationforSportandPhysicalEducation全国体育与体育教育协会. 　　Also,shesaysnotallstatesrequireP.E.teacherstobespeciallytrained.Untrainedteacherscouldbelesslikelytorecognizeunsafeconditions. 　　CherylRichardsonalsopointstooneofthestudy'sfindings--thatinjuriesareoftentheresultofcontactwithapersonorastructure.Thistellsherthattheteacherswerenotgivingeachstudentenoughspacetomovearoundsafely. 　　Sixactivitiesproducedseventypercentofallinjuries:running,basketball,football,volleyball,soccerandgymnastics. 　　ThestudyappearedonlinethisweekinPediatrics,thejournaloftheAmericanAcademyofPediatrics美国儿科协会. 　　Theresearcherssaylargerclasssizesareanotherpossiblereasonfortheincreaseininjuries.Largerclassescanmeanlesssupervision.TheNationalAssociationforSportandPhysicalEducationsaystwentytothirtystudentsinaP.E.classshouldbethelimit.