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Assessment of physical exposure in relation to work-related musculoskeletal disorders--what information can be obtained from systematic observations? 2.pdf

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Downloaded from www.sjweh.fi on May 27, 2018 Original article Scand J Work Environ Health 1994;20 :30-45 Assessment of physical exposure in relation to work-related musculoskeletal disorders--what information can be obtained from systematic observations? by Kilbom A
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  Downloaded from www.sjweh.fi on May 27, 2018 This work is licensed under a Creative Commons Attribution 4.0 International License.Print ISSN: 0355-3140 Electronic ISSN: 1795-990X Copyright (c) Scandinavian Journal of Work, Environment & Health Original article Scand J Work Environ Health 1994;20 :30-45 Assessment of physical exposure in relation to work-relatedmusculoskeletal disorders--what information can be obtainedfrom systematic observations? by Kilbom A Affiliation:  National Institute of Occupational Health, Solna, Sweden. The following article refers to this text: 2010;36(1):1-80 This article in PubMed: www.ncbi.nlm.nih.gov/pubmed/7846490  Scand J Work nviron ealth 1994,vol20,specialissue theobservationincreasesbecauseseveralclassesofposturesareincorporated,theconsistencybetweenobserversdecreases 39 .ThisdecreaseconfirmstheresultsofvanderBeekandFransson-Hall.AspointedoutbyKeyserling,differencesbetweenobservers,whenrecordingthepostureofacertainbodyregioninseveralclasses,areduetodisagreementsconcerningtheboundariesofadjacentpostures.Amongthebodyregions,neckpostureappearstobethemostdifficulttoassessaccurately,evenwithonlythreeclasses Fransson-Halletai,unpublishedmanuscript .Intraobserverreliabilityappearstoberelativelyhigh,andhigherthaninterobserverreliability,evenwithseveralmonthsseparatingrepeatedobservationsofavideorecording 39,60,Fransson-Halletai,un publishedmanuscript . Internalvalidity Theinternalvalidityofobservations ie,theextentofagreementbetweenobservationsandother,moreaccuratemeasurements haveonlybeentestedforafewmethods.Keyserlingcomparedresultsobtainedinasimulatedreal-timeobservationwithaframeby-framevideoanalysisandobtainedahighdegreeofagreementfortheproportion   timespentwiththebackinaneutralpositionandinsevereflexion,theshouldersinaneutralpositionandinmildandsevereflexionorabduction 39 .Observationsofbackandleft-rightshouldersweremadeinthreeseparatesessions.Timespentwiththebacktwistedorbentwasoverestimated,probablyduetothedifficul tyoftranslatingatwo-dimensionalvideoobservationintothreedimensions.BurdorfvalidatedOWASobservationsoftrunkflexion  > 20degrees usinginclinometerrecordingsandfoundasignificantcorrelationbetweenthetwomethodsforthetimespentinforwardflexion,duringbothsedentaryanddynamicwork 61 .However,largedifferencesbetweenthetwomethodswereobtainedforindividualsubjects.Especially,theproportionoftimeinforwardflexionofthebackwasvastlyoverestimatedbysedentaryworkers.Inarecentstudy,Leskinenetal unpublishedmanuscript validatedthePEOmethodusingvideorecordingsandanoptoelectronicrecordingsystem sel-spot ,Measuredtrunkflexionsbetween50and60degreesweresystematicallycodedasexceeding60degrees,buttherewasgoodagree mentbetweentheproportionoftimeobservedasexceeding60degrees,butrecordedasexceeding50degrees.Therequirementforrecordingtrunkrotation ie,   45degrees provedunrealistic,asitdidnotoccurintherealisticrangeofthetasksstudied.Observationsofneckpostures  > 20degrees wereunreliablewithregardtobothdurationandfrequency.Theauthorsconcludedthattherewasahighdegreeofagreementbetweenmeasuredandobserveddatafordurationsofsustainedpostures exceptneckflexion andlong-lastingrepetitiveactivities typing . 38 Thefrequencyofclearlydistinguishableactionslikeliftscouldalsoberecordedaccurately.Evenreducingthenumberofexposuretypesbyhalfdidnotsubstantiallyimprovetheagreementbetweentheobservationsandmeasurements,andthisresultwasinterpretedasindicatingthatdemandsonthedataprocessingcapacity   theobserverduringsimultaneousmeasurementsofseveralfactorsweretoohigh.Fordetailedobservationsofpostures,itappearsthattheabilityoftheobservertodistinguishbetweenadjacentangularsectors eg,moreorlessthan60 degreesofflexion isthecrucialproblem.Inanexperimentalstudy,Ericsonetal 62 comparedtheobservationsobtainedbyexperiencedergonomists, directobservations,andobservationsfromvideorecordingstothoseobtainedbyavideopositionanalyzer.Theobservationsweremadeinthesagittalplane.Observationsofthetrunk,neck,andupperarminclinationscouldbemadewithanaccuracyofaboutfivedegreesduringstaticconditionsandwithsomewhathigheraccuracyduringdynamicconditions,anddirectobservationsdidnotdifferfromthoseobtainedfromvideorecordings.Theaccuracywassomewhatbetterclosetohorizontalandverticalthanintheintermediaterange.SimilarresultswereobtainedbyvanderBeeketal 47 whentheycomparedobservationsfromaphotographwithoptoelectronicrecordings.Obviouslytheseresultswereobtainedunderoptimalconditions,andinamorecomplexenvironmentaccuracyislikelytobelower.Nevertheless,systematicallytrainedobserversshouldbeabletoobserveangularsectorsandthusachievemorethanameredichotomousobservationofposture.  xternalvalidityandapplicability Forthepurposeofthisreview,externalvalidityis definedastheabilityofanobservationmethodto identifyphysicalexposuresassociatedwithanincreasedriskofmusculoskeletaldisorders.Prerequi sitesforhighexternalvalidityare i acorrectunderlyinghypothesis ie,arelationshipbetweencertainphysicalexposuresandmusculoskeletaldisordersexists and ii anexposureobservationmethoddesigned operationalized topermitexposurestobeassessedwithsufficientaccuracy.Eventhoughtheunderlyinghypothesismaybe correct,thelatencytimebetweenexposureandtheovertsymptomordiseasemaybetoolongtopermitanassociation to bedemonstratedinacross-sectionalstudy.Thishoweverisaprobleminherentforanymethodusedtoassesscurrentphysicalexposure,beitbydirectmeasurement,observation,orquestionnaire.Table2summarizessomeepidemiologicstudiesinwhichobservationmethodshavebeenusedtoquantifyexposure.Thetablecontainstwostudiesinwhichneckflexion,shoulderelevation,andabductionareassociatedwithshoulder-neckdisorders.In fourstudiesrepetitivity,force,andspeedofhand-  armmovementshavebeenassociatedwithforearm wrist-handdisorders,andintwostudiesabentor twistedbackhasbeenassociatedwithlow-backdis orders.Onestudyhasdemonstratedarelationship betweenthedurationofstandingandback,lower limbandfootsymptoms,andanotherhasshownan associationbetweenaccidentsandbackpostureor lifting.ConsideringthattableIcontains19observation methodsforposturalassessment,towhichcanbe addedNIOSH sprocedureforevaluatingliftingand themethodofSilversteinetalforrepetitivework, theapplicationofobservationmethodsformuscu loskeletalepidemiologyiscertainlyverysparse. Theirapplicationforergonomicpurposesismore common,buteventheneachgroup of researchersappearstofavorthedevel opment ofanewmethodratherthantheuse of onedevelopedbyothers.As amatter of fact,onlytheOWASmethodhasbeen appliedwidelyforepidemiologicandergonomic purposes.   maybethatmostmethodshavebeen documentedonlyinthelastsixorsevenyearsand thatmoreapplicationscanbeexpectedastheimpor tanceofexposureassessmentbecomesmoreevi dent.Eventhoughtable2demonstratesthatobser vationmethodscanbeusedtostudytherelationship betweenphysicalexposures and musculoskeletaldisorders,morestudiesneedtobeperformedbefore theexternalvalidityofobservationmethodshas beenproved. Operationalization Thedesign of scales,thenumber of exposurefactorsrecordedsimultaneously,themodeofobserva tion(film-videoordirect),themodeoftimemoni toring(continuousortimesampling),andtherecord ingsystem(pencilandpaperorcomputer)allcon stituteaspects of theoperationalizationofanobser vationmethod.Allofthesefactorsp rof oundlyinfluencethereliabilityandvalidityofthemethod. Pencil and paperorcomputerizedregistration  Mostobservationmethodsofrecentyearsarecom puterized(ie,theinternalclockofthecomputeris usedforkeepingtimeandautomaticallyrecording thedurations),andeachexposurefactorisassigned onekeyoracombinationofkeysonthecomputer keyboard.Therecordingscaneitherbeperformed directlyattheworkplace,byuseofaportableor hand-heldcomputer,orfromvideorecordingssub sequentlyanalyzedinthelaboratory.Themostwide lyusedobservationmethod,OWAS,hasnowalso beencomputerized (33). Thegainsofcomputeriza tionaretwofold.Thetimeneededforrecordingis reduced,andtheentirecognitivecapacityoftheob serverismadeavailableforobservationratherthan forkeepingtime.Uscofaportablecomputerhasthe advantageofenablingdirectfeedbackofdetailedin formationfromthescreentotheobserver.Thereby Scand   WorkEnvironHealth 1994,vol20,specialissue errorsinregistrationcanbedetectedimmediately. Moreover,forteachingandtrainingpurposesthis feedbackisvaluable.Asmallhand-heldcomputer provideslessdetailedfeedbacktotheobserverbut is,ontheotherhand,easiertocarryattheworkplace. ExperiencewiththePEOmethodshowsthatintra andinterobserverreliabilityisnotnegativelyaffected bytheuseofhand-heldcomputersversusportable computers,providedtheobserversaretrained(Frans son-Halletai,unpublishedmanuscript). Directorfilm videoregistration The advantage of directobservationisthatposturesarelikelytobere cordedmoreaccurately,sincehumanvisionisthree dimensionalwhereasafilm-videorecordingisre ducedtoatwo-dimensionalimage.Inanexperimen talstudy,Ericsonetal(62)didnotfindanydiffer encesbetweenobservationsregistereddirectlyand viavideorecordings,providedtheobservationswere performedinthesagittalplane.Paul Douwes(64) comparedatwo-dimensionalassessmentofpostures fromphotographswithathree-dimensionalevalua tionusinganoptoelectronicsystem.Theirresultsin dicatethattwo-dimensionalrecordingsgivesuffi cientaccuracy,aslongassomeguidelinesforthe reduction of perspectiveerrorsarefollowed.Keyser lingnotedhoweverthattheobserversmisjudgedthe proportionoftimespentwithatwistedbackwhen theassessmentwasdonefromavideorecording, whileadirectassessmentwasmoreaccurate (39). Stetsonetal (45), comparingdirectobservationswith avideoanalysisofhandandwristposturesandgrip types,concludedthatdirectobservationsweremore accurate.Inaddition,itiseasiertomovearounda workplaceandsecureoptimalviewingangleswhen theobservercarriesonlyahand-heldcomputerrather thanavideocamera,whichrequiresadditionalat tentionandadjustments.Ontheotherhand,avideo recordingcanbeanalyzedrepeatedly,andthisabil ityisnecessarywhentasksdoneatahighworkpace arebeingobserved,andalsowhenmanyexposure factorsarerecordedsimultaneously.Therefore,di rectregistrationattheworkplacecanonlyberec ommendedwhenonlyafewvariablesarebeingas sessedorwhentheworkpaceisslow. Realtimeortimesampling  Acertainexposurecan beregisteredwhenanewsituationarises,forexam ple,whenaposturechangesoramanualhandling activityisperformed (19, 39 44 45 47 65, Fransson-HalletaI,unpublishedmanuscript).Thisisan event-drivenprocedure,inrealtimeorsimulatedreal time,anditenablesthecomputerprogramtoassess thesequence,duration,andfrequencyofeachevent andeachseparateexposurefactor.Alternatively,reg istrationscanbeperformedatcertainintervals (whichmayberegularorirregular,dependingonthe regularityofthe job .Suchatime-samplingproce dure,withsamplingintervalsof 10  3 sbasbeen 39  Scand   Work nviron ealth 1994.vol20.specialissue  ble   Associationsbetweenobservedphysicalexposuresand mus ulo skeletaldisordersinsomeepidemio logi studies.(OR = oddsratio)AuthorFeuerstein   Fizgerald1992(19)Fransson-Halletal (unpublishedmanuscript)Jonssonetal1988(21) Typeof stu y Case-referentCross-sectionalOne-andtwo-year follow-upOccupationalgroupSignlanguageinterpreters, 16withand13withoutpain Automobileassembly-line workers,11fromlowand9fromhigh-symptomdivisions69electronicsassembly workersExposureassessmentObservationofstandardinterpretationtaskHandPEO,seetable1; observationofrepresentativeworktasksVIRAatstartofstudy;seetable1. Karhuetal1977(30)Cross-sectional120maleworkers(4occu-RandomselectionoftwoorBurdorf1992(69)pationalgroups)versusthreeworkersperjob;52referentsobservationofback,legsand lifti ngbyOWAS,interval20s, allactivitiesrecorded Keyserling1986(39) Case-referentAutomobileassemblySeetable1,some proxy  Punnettetal1991(63) workers:workersalsoanalyzedwhen 95casesreportingobservationofcasewasnot backpain,124referentspossiblewithoutbackbainKilbometal1986(44) Cross-sectional96femaleelectronics VIRA,seetable1, assemblyworkersobservationoftypicalwork tasks,alsoworkhistoryand productivityRyan1989(42) Cross-sectional513supermarketworkersSeetable1;samplingfor 30min,onetotwoworkers perstoreobserved Silversteinetal1986(52)Cross-sectional 574industrialworkersObservationofindividualrepresenting34jobs,jobs,videoandelectro- >20workersperjob myographyoftypicaljobs; highrepetitivitycycletime <30s,highforce>4kg, lowforce<1kg Silversteinetal1987(53)Cross-sectional652industrialworkersSeeabove representing39jobs, >20workersperjob Wickstrometal1985(18)Cross-sectionalConcretereinforcementObservationofallworktasks workandhousepain ting for272hateightworksites; twoobservers,seetable1 used,forexample,inOWAS 30 andposturetar geting 24 andby Baty etal 46 ,Ryan 42 ,Wick strometal 18 ,andvanderBeeketal 48 .Pro videdsamplingintervalsarechosenappropriately withregardtothepaceofthe  o b,timesamplinggivesareasonableapproximation o thedurationandfrequencyofeachexposurefactor.TheROTAmeth oddevelopedbyRiddetalprovidesthepossibility ofusingeitherrealtimeortimesampling 37 . Real-timeproceduresprovidemoreinformation butputverylargecognitivedemandsontheobserver 40 infastjobs.Thesolutionmaybetouserepeatedob servationsofavideorecordinginslowmotionortwo observersinsteadofone,asdonebyWickstromet al 18 andproposedbyvanderBeeketal 48 .So fartheadvantageofreal-timeobservationsovertime samplinghasnotbeenprovedconclusively.Although informationgatheredonthedurationofeach exposureeventislikelytobeoflargepotentialval ueforunderstandingtheetiologyofmusculoskele taldisorders,ithasnotbeenusedinepidemiologic studiessofar.
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