Racing Surfaces: Current progress and future challenges to optimize consistency and performance of track surfaces for fewer horse injuries.

Transcription

1 Racing Surfaces: Current progress and future challenges to optimize consistency and performance of track surfaces for fewer horse injuries. White Paper Sponsored by Michael Mick Peterson, PhD, University of Maine, United States Lars Roepstorff, DVM, PhD, Swedish University of Agricultural Sciences, Sweden Jeffrey J. Thomason, PhD, University of Guelph, Canada Christie Mahaffey, MPhil, University of Maine, United States C. Wayne McIlwraith, BVSc, PhD, Colorado State University, United States Updated: April 27, 2012

2 This white paper has been drafted as a collection of published scientific papers and data. It is considered a work in progress and will be updated as new scientific studies and track data become available.

3 PREFACE Racingsurfaceshavereceivedagreatdealofattentioninthepopularandfancoverageofhorse racing(seeforexampleschulman2007,rezendes2007,finley2010).additionally,tracksurfaceshave recentlybeenatopicofdiscussioninthescientificliterature.threegeneralareasofinquiryhave emerged:(1)characterizationoftheinteractionofthehoofandtheground,(2)in situtestingofthe surfaceand(3)specificcharacterizationofthematerialsusedintheracetrack.ageneralunderstanding ofthehoofgroundinteractionhasbeenfacilitatedbydynamicaccelerometry(dallap Schaer2006)and horseshoestudies(setterboetal.2009)overthelastdecade.someofthisinformationissummarizedin reviewsoftheloadingofthegroundandthehoof(johnstonandback2006,thomasonandpeterson 2008).Someworkhasalsolookedatin situtestingofthesurface(petersonetal.2008)including differencesintypesofsurfaces(setterboetal.2008,thomasonetal.2007)andtheeffectsof maintenanceandweatheronthetracksurface(petersonandmcilwraith2008,petersonetal.2010). Morerecentworkwhichhasemergedonthetestingofthematerialsusedinracingsurfacestoboth characterizethematerials(bridgeetal.2010)andtothelaboratorytestingoftheirresponsetoloads thatmimic theloadingofthesurfacebythehoof(bridgeetal.2010a,bridgeetal.2011). Inthesepapersandinthediscussioninthepopularpress,acommonthreadunderliesthe discussion:doesaracingsurfaceexistthatcombinesperformanceandconsistencywithsafety? Technicallypreciseanswerstothisquestionwillrequirethatcommondefinitionsofkeyterminologybe developedregardingtheconditionofthesurface.auniformvocabularycanbeusedtolinktothe epidemiologicalliteraturetodescriptionsofthesurface,whichwillenableinjuriestobelinkedto particularsurfacesandconditions.eventhen,however,therelationshipbetweensurfacesandequine injurieswillcontinuetopresentadditionalspecificchallengesduetothedifferencesintypesofinjuries andtheeffectoffactorssuchasjointdiseaseontherisktoahorseduringaparticularevent. Injury,inparticularcatastrophicinjury,isamulti factorialeventthatinvolvesthecomplex interactionofanumberofriskfactorsincludingbutnotlimitedtomedication,genetics,andtraining. ThefullscopeoftheproblemissummarizedinFigure1,inwhichtrack surfacepropertiesareisolatedas thefocusofthispaperfromamongseveralotherknownriskfactorsforinjury.giventhatthe overwhelmingmajorityofcatastrophicinjuriesshowclearevidenceofpreexistingdisease(norddinetal. 1998,Stover2003),improvedracingsurfaceshavethepotentialtoresultinanimprovementinthe safetyofhorseracingforbothridersandhorses.musculoskeletalinjurieshavealargeadverseeffecton thethoroughbredracehorseindustryduetobothfatalinjuriesthathavelowprevalenceandmilder injuriesthathaveahighprevalence.candidatesforinjurypreventionthathavebeenproposedinclude improvedmanagementpracticestominimizetheincidenceoflowhoofheelangle incorporationofmorefrequent,shorterhighspeedworksorracesinexerciseregimens avoidanceofexcessiveaccumulationofhighspeeddistancesovershortperiodsoftime recognitionandrehabilitationofmildinjuries maintenanceofuniformityofracingsurfacesamongracetrackswithingiven environmentalconditions(riggs2002,stover2003).

4 Anotherspecificallydocumentedriskforinjuryiswhenawell trainedhorsechangesfromone typeofsurfacetoanotherandatthesametimeisexpectedtoperformatmaximumcapacity,for examplegoingfromtrainingonasoftsurfacetocompetitiononahardsurface. Otherthanthequalityofpreraceexaminations,however,noriskfactorhasanimpactonall horsesracingataparticularvenueonasingledaygreaterthanthequalityoftracksurfaceconstruction andpreparation.therefore,thedevelopmentofaconsistentandwell characterizedracingsurfaceisan importantgoaloftheindustry.thisrequiresthatatoolexistthatcanobjectivelyquantifythefunctional propertiesofsurfaces,particularlythosepropertiesinthecausalpathwaytoinjury.infact,theroleof surfacesinthedebateoverthesafetyofracingissufficientlyimportantthatitmaybethatmanyofthe otherchallengesfacingtheindustrywillonlybeaddressedinasystematicmanneraftersignificant progresshasoccurredinunderstandingwhatconstitutesasaferacingsurface.thus,improvedracing surfacesshouldberegardedasasteponthepathtoimprovedsafetyoftheracehorseandresultingina safersportfortheriders. Thisdocumentconsidersonlytheeffectofsurfacesontherisktothehorse.Eventhough optimizationofsurfacesalonewillnevereliminatecatastrophicinjuries,andmaynotevenbeaprimary factorinmostinjuries,itishighlylikelythatachievingwell designed,uniformsurfaceswillbenefitthe horses,theridersandthesport.however,theabsenceofwell acceptedcharacterizationmethodsand basicscienceofracingsurfacesisasignificantobstacletoimprovedperformanceandsafety.inthe effort,toimprovesurfacesitiscriticaltolookatthefactorsthatcontroltheperformanceofracing surfacesinthecontextoftherelevantbiomechanics,thedifferenttypesofsurfaces,andpotential testingandmaintenancestrategies. BACKGROUND Defining the scope of the problem Asafesurfaceisoneforwhichthesurfaceproperties(tobedetailedlaterinthepaper)have beendesignedtopreventinjury.currentevidencesuggeststhatconsistencyofeachsurfaceandlimited variabilityamongsurfacesseenbyeachhorsearemoreimportantthantheexactvaluesofeach property.consistencyallowsforthehorsetoadaptthroughtraining.therefore,agreater understandingoftheroleofthetrackinthecausationofinjuryisaprerequisiteforsafertrackand surfacedesign.historically,theindustryhastakenatrial and errorapproachtobuildingasafesurface, withlittlestudyintotheactualcausesofinjury.ineffect,thesystemsofarhasbeentolaydowna numberofsurfaces,testtheproperties,andcomparefrequenciesofinjuryamongsurfacetypes. Unfortunately,asameansofidentifyingthequalitiesofasafetrack,thissystemiscumbersomeand expensive,bothintermsofthemoneyspentonconstructionandtestingandintermsofthecostto horsewelfare. 2

5 Ascientificallymorerobustapproachistoaimforunderstandingthecombinationsandranges ofpropertiesthatmakeasurfacesafeandwhythosecombinationspreventinjury.thisapproachis complicatedbecausetherearefourinterveningcategories degreesofseparation,ifyoulike between thesurfacepropertiesandknowinghowtopreventthemanyandvariedinjuriesthatoccurinrace horses.figure1showshowoptimumtracksurfaceconstructionandpreparationmustoccurincontext otherkeyfactors:1)horse hoof trackinteraction,2)loadingonspecificanatomicalstructures,3) primarycausesofinjuries,and4)thefeaturesoftheinjuriesthemselves. Risk factors for injury Track-surface properties:! Vertical hardness! Horizontal shear! Rebound timing Other factors:! Nutrition! Training regime! Difference between training and racing surface! Banking and layout of track! Genetics! Conformation! Shoe type Figure1.Apathwayfromtrackpropertiesasariskfactortothedesirableoutcomeofpreventionof injury,viathepostulatedmechanicalunderpinningsofthecausesofinjury,andtherelevantfeaturesof injuriesoncetheyoccur. Horse hoof trackinteraction Energyfromtheshockofcontactwiththegroundandforces owingtochangingthemomentumofthelegsandbodytransferthroughthehoof.theamountof energyandthemagnitudeofforcesdependstronglyonthepropertiesofthetracksurface,butthere areseveralcomplicatingfactors.first,eachsurfacepropertyhasadifferenteffectontheenergyand forcesexperiencedbythehorse.second,theenergyandforcemagnitudeschangethroughoutthe footfall(stance)andswingphase.third,shoesmodifythemechanicsatthehoof trackinterface. Fourth,thehorse sownconformationandanatomicalconstructioncontributetothemannerinwhichit interactswiththetrack,soitisimportanttostudyhowtheinteractionvariesamonghorses. 1. Horse-hooftrack interaction:! Stance! Primary impact! Secondary impact! Support! Breakover 2. Loading on specific anatomical structures:! Bones! Joints! Tendons! Ligaments! Muscles 3. Causes of injury:! Single-event overload! Pathological biological response over time! Muscular fatigue! Repetition failure (material fatigue) 4. Features of injuries:! Location! Severity! Frequency! Ease/difficulty of accurate diagnosis Desirable outcomes:! Prevention of injury Loadingonspecificanatomicalstructures Thestaticanddynamicloadsonthelegstressthe materialsofeveryanatomicalstructureinthelegincludingeachbone,muscle,tendonandligament. Eachstructureexperiencesitsownresultinglevelofstressatanystageofthestanceandswing. Injuriesoccurwhenthesestressesexceedtolerablethresholds.Thespecificthresholdlimitsaredefined 3

6 bothbyeachspecificeventandbythestresshistoryoftheanatomicalstructure.forthisreason,being abletodeterminetherangeofstressexperiencedbyeachstructureisthekeytounderstandinghow injuriesoccur. Causesofinjury Injuriescanprincipallyoccurintwodifferentways,eitherasacatastrophic injuryduetoacuteoverloadorasdegenerativechangesduetorepeatedminoroverload.acute overloadresultsinimmediatetraumaticfailure,usuallyofabone.degenerativechangesoccurbecause bonesandmusclesaremadeoflivingtissuescontainingcellsthataresensitivetolevelsofstress.below athresholdlevelofstress,bothtypesoftissueshownormal,healthyadaptiveresponsestochanges: increasethestressduringexerciseandboneandmusclemassincrease.eventendonsandligaments showthiskindofresponse.however,ifthethresholdstressisexceededrepeatedly(forexample,during everyfootfallatspeed),theresponsecanbecomemaladaptive,causingpathologicaltissue degeneration.thisinappropriateresponseiscommoninthebonesandjointsofracingand performancehorses.thestressisnotenoughtocauseimmediatefailure,butthedamagecausedby degenerationreducesthelevelofstressatwhichabonewillfail. Featuresofinjuries Accuratediagnosisofinjuries,togetherwithinformationontheirlocation, severity,andfrequencyofoccurrence,providevaluableinformationincombinationwiththecategories ofdatadescribedintheprecedingthreesubsections.togethertheyleadtoamodelfordirectlylinking trackpropertieswithinjury. Linkingtrackpropertiestoinjury Achievingthegoalofmakingadirectconnectionbetween trackpropertiesandspecificinjuries(notsimplyinjuriesingeneral)isamajorstepinminimizingthe effectofthetrackontheoccurrenceofinjury.fullunderstandingofthecausesofspecificinjuriesisan elusivegoal.butwehavethewherewithalwithcurrenttechnologytoestablishalinksufficientlywellto reducetheriskofthetrack,i.e.,maketracksassafeaspossible.inconcept,anappropriateprogramof researchcanbedescribedrelativelyeasily.however,thecostandthelogisticsofmountingtheprogram wouldbeverychallenging.simplystated,usingsomeofthemethodsdescribedbelow,itisrelatively easytocombinethemeasurementoftrackpropertieswiththoseofthehooftrackinteractionbydirect measurementfromhorsesonthetrack,atspeed.ifthesedataforasufficientlylargesampleofhorses arecombinedwiththefeaturesofthoseinjuries(accuratediagnosis,location,severityandfrequency),it shouldbepossibletofindconcretelinksbetweentrackpropertiesandoccurrenceofinjury.the challengefacedbysucharesearchprogramistoeffectivelycharacterizebothindividualvariations betweenhorsesandvariationsinsurfacesandconditionstoeffectivelyrepresenttherisktohorses underactualracingandtrainingconditions. Interaction of the horse and hoof with the track Atracingspeedsreaching38mph(17m/s),thehoofhitsthetrackapproximately150timesa minute,remainingonthegroundinthestancephaseforasixthofasecondeachtime.theshort durationofthestancehidesfromoureyesseveralstagesthataredistinctiveintheirmechanical characteristics(figure2)andthathaveverydifferentpotentialforcausinginjury.forthepurposesof thispaper,weidentifyfourstages:primaryimpact,secondaryimpact,support,androllover.the mechanicsofeachstageisdependentonthedesignofthetrack(e.g.,radiusofturns,angleofbanking), 4

7 andthepropertiesofthetrack.thisdependencegivesusthebasisforreducinginjuryratesby modifyingtrackproperties,becausetheshockenergyandforcestransmittedbetweentrackandhoof underliethecausesofinjurytobonesandsofttissuesinthewholeleg. Figure2.Stagesofthestanceshowingthedifferencesamongthestagesinacceleration(red)andground reactionforce(grf)(blue).atiltedgrfarrowindicatesthatbothverticalandhorizontalcomponentsof GRFarepresent.Thearrowshowsthedirectioninwhichthegroundispushingthehorse. Itislikelythatinjuriescausedbytheshockofprimaryimpactareconfinedwithinthehoof e.g., Primaryimpact Whenthehoofimpactstheground,itismovingdownwardatahighrateof speedbutismovingforwardrelativelyslowly(becausethebackwardswingofthelegonthebody almostcancelsouttheforwardspeedofthebody).essentiallythehoofhitsvertically,liketheheadofa droppedhammer.asthehoofmeetstheground,itdeceleratesrapidlytowardszerovelocity(within1 3millisecondsonafirmsurface).Therateofdecelerationisoftheorderof100gonracingsurfaces (Dallap Schaeretal.2006).However,thesofttissuesofthehoofdampentheshockofimpact(Guståset al.2001),asdoesthetracksurfaceifithastheappropriatecushion.forcesonthefootarerelatively low,becauseonlythemassofthehoofandpasternparticipatesinthiscollision.sincethemassislow, forcesareusuallykeptwithinthelimitsofstrengthofthebonesandsofttissuesofthehoofandlimb. Magnitudesofdecelerationandshockenergyduringprimaryimpactareextremelysensitiveto verticalhardnessofthesurface.metalshoesmayexacerbatetheproblemforcertaininterfaces, althoughthereisinsufficientevidencetobesure,collapsedheels,somequartercracks,andotherissues 5

8 havebeenassociatedwithmetalshoes.thisisbecausetheshock absorbingstructuresofthehoof (frog,digitalcushion,heelbulbs,laminarjunction)absorb70%oftheenergy,basedontestingon cadaverlegs(willemenetal.1999,lanovazetal.1998)andinvivoexperiments(guståsetal.2001).by constrainingthehoofmetalshoeshavemayreducetheabilitytoabsorbtheenergyfromtheimpact. Secondaryimpact(slideandstop) Assoonasthehoofisatrestonthesurface,thebodyof thehorse,whichisstillmovingforward,collideswithitsownimplantedandstationaryleg(ruinaetal. 2005).Thebodytendstopushthelegforward,forcingthehooftoslideandthenstop(Pardoeetal. 2001).Forcesactingonthelegnowbegintorisedramatically;asthehoofpushesintotheground,the groundexertsanequalandoppositeforce,knownasthegroundreactionforceorgrf,whichcanbe brokendownintoverticalandhorizontalcomponents.thisforceistransferredbackupthelegandis absorbedbythemusculoskeletalsystemofthehorse(clayton2004). Whilethehoofisslidingandstopping,theGRFhasahorizontalcomponentthattendstoretard orbrakethemotionofthebody,aswellasarapidlyrisingverticalcomponentastheanimal sbody weightcomestobearontheleg(hjerténanddrevemo1994). Secondaryimpacthasthepotentialtohavealargeroleincausinginjury.Duringthenormal slide stopactionofthehoofthatoccursinthisstage,thecoffinbonemaybeforcedforward, compressingthelaminarjunctionbetweenitselfandthecapsule.thisactioniscertainlyplausible, thoughithasnotbeenconclusivelydemonstrated.ifitdoesoccur,itmightbeonecauseofbruising. Ifthefootslipsforwardexcessively,thisactionhasthepossibilityofforcingthedigitalflexor musclesintorapid,unpredictedeccentriccontraction,whichcancausetearswithinamuscle.ifthefoot comestotoorapidahalt,itwouldexacerbateanyforwardmotionofthecoffinbone,asdescribedin theprecedingparagraph.ofpossiblygreaterconsequence,shorteningthedurationoftheslidewill increasethemagnitudeofthehorizontalcomponentofthegroundreactionforce,exertinglarger thannormalbendingmomentsonthecannonbone(pratt1997).evensmallincrementsinbendinginduce largestressesinlongbonessuchasthecannonbone. Akeyinreducinginjuryduringthisstageismatchingthetractionofshoestotheshear propertiesofthetrack.itis,inprinciple,easytomeasurethegripofgrabsandcaulksofarangeofsizes andshapesonavarietyofsurfaceswithdifferentshearproperties.thesedatacouldpotentiallybe madeintoatablesothatwhentheshearpropertiesofatrackhavebeenmeasured,thetypesof grippingdeviceonashoethatareappropriateforthetrackcouldbereadfromthetable. Support Thisstageoverlapswithsecondaryimpactandextendsthroughmidstanceandinto therolloverstage.thedistinctivemechanicalcharacteristicofthisstageistheriseandfallofthe verticalcomponentofthegrf,asthelimbpreventsthebodyfromfallingduetogravityandaccelerates itupwardintothenextswingphase.theverticalgrfpeaksaroundmidstance,andmayreach2.4times thebodyweightoftheanimalataracinggallop(witteetal.2004). Thesheermagnitudeoftheforcesonthefootmidstanceimplicatethisstageverystronglyin causingtraumaticbonefracturesandtendonandligamentrupturesorstrains.inaddition,joint 6

9 loadingsatthistimewillexacerbatechronicjointproblems.aftermidstance,thebrakinghorizontalgrf changestoapropulsiveforce.atthistime,appropriatetractionbetweenshoeandsurfaceiscritical. Rollover Thisstageisthelastphaseofunloading,beginningassoonastheheelsleavethe surface.bothverticalandhorizontalgrfarefallingfrom30 50%oftheirpeakvaluestowardszeroat toeoff.thehoofitselfunrollsthenpushesofffromtheground. Thisstageisimportantinthatalteringthedurationofrolloverstronglyaffectsthekinematicsof thelimbduringtheswingphase,whichinturnaffectsthekineticsofthenextstance.forcingashorter orlongerstanceunderthoseperformanceactivitiesthatinducehigherloadingconditionswillaffectthe forcesandstressesactingonbonesandsofttissues.ifmoremuscularcontrolisnecessarytoperform theactivity,muscularfatiguemaybecomeafactorininjury.ifbreakoverandtoe offaredelayed, residualtensioninthedeepandsuperficialdigitalflexortendonsmayflickthefootbacksufficientlyfast thatrate dependentinjurytothosetendonsispossible.thisspeculativesuggestionissupportedby workthatshowshighermagnitudesofaccelerationofthehoofaftertoeoffingallopingthoroughbreds thanthedecelerationsonimpactwiththesurface(schaeretal.2006). How the track influences hoof forces Theresistanceofthetracktotheimpactandloadingofthehoof(Burnetal.1997)determines therateofloadingofthelegandthustheaccelerationsandforcesencounteredinthejointsofthe horse(ryanetal.2006,setterboetal.2009).earlystudiesontrackandsurfacedesigntopreventinjury introttinghorsesweredoneinsweden(fredricsonetal.1975,drevemoandhjérten1991).the combinedloadingexperiencedbythelegisdependentonboththeverticalandhorizontalresponseof thesurface(zebarthandsheard1985).thesecomplexmovementsofthedistallimbhavebeen elucidatedininvasiveandnon invasivemodelsthatdemonstratesignificantdifferencesintheloadingof thedistallimbasrelatedtosurfaces(chateauetal.2006,spännaretal.2004).hence,boththe horizontalandverticalcomponentsmustbeexaminedwhendeterminingthedynamicresponseofthe surface.intheverticaldirection,thetrackdeceleratesthedownwardtravelinghoofthrough compactionoftheloosetoplayercushiononadirtorsyntheticracingsurface.theprofileofthetop sectionofaturfsurface,however,ismorecomplexandmayincludeatoplayerthatiseitherloosened mechanicallyorthatmaybecoveredbyasurfacelayerofrootsandorganicmaterial.asthesoilortop layeroftheturfcompacts,itbecomesstifferandmoreresistanttofurthercompaction,bringingthe hooftoastop(thomasonandpeterson2008).oncethemotionofthehoofhasbeenslowedorhas stopped,theweightofthehorseisdynamicallytransferredtothehoofandthentothehardersurface materialbeneaththehoof.thisdynamictransferoftheweightofthehorsetothehoofisthesourceof theacceleration,resultinginpeakloadsthatmayapproach2.5timesthebodyweightofthehorse. Thehardnessofthetrackinfluenceshowquicklythefootisdeceleratedandthenthestiffness ofthetrackwhentheloadisbeingapplied.thisrateofdecelerationcontrolsthestrainthatis transferredtotheleg,andstiffersurfacesthereforeresultinhigherpeakloads.repeatedloadingtothe bonecancausebothmicrofracturesandcatastrophicfractures(radinetal.1972).anincreased hardnessofthesurfacealsoincreasespeakloadsandloadrates(goldsmith2001).boththeacuteand therepetitiveimpulsiveandexcessiveloadinghavebeenproposedtobebiomechanicalriskfactors 7

10 (Radinetal.1972,Johnstonetal.1995).Therefore,itisreasonabletoexpectthataboveacriticalstrain andstrainrate,thereliesthepotentialforthepropagationofcracksinthebonematrixwhichcanresult incatastrophicfailureofthebonesintheleg.thisisadynamicprocessthatisnotdependentstrictlyon theloading,butalsoonthedegenerationandremodelingofthebone(ehrlichandlanyon2002). Hard tracksgeneratealargeimpactforceandhighfrequencyvibrationsduetotherapiddecelerationofthe hoofoveraveryshorttimeperiod(barreyetal.1991).ona soft track,thedecelerationoccursovera longertime,reducingthepeakimpactforceandreducingtherateatwhichthestraininthehoofis applied.however,withtoosoftofacushion,thesoilcancontinuetocollapseasthehorsetriestopush off,resultinginalossofforwardmomentumandspeedwiththeassociatedincreaseinenergy expenditureandresultingfatigue(whichisanimportantcausalfactorininjury).however,itis importanttorecallthatmovementandloadingofthelowerlimbisalsoaffectedbyfactorssuchaslimb conformation,shoematerialandtypeofshoeaswellasthegroundsurfacecharacter(barreyetal. 1991,Willemenetal.1999,Roepstorffetal.1999,Pardoeetal.2001). Thehorizontalresponseofthesurfacealsoplaysakeyroleindeterminingtheloadingoftheleg. Duringthefirstportionofthestancephase,thehoofslidesforwardbeforecomingtorest(Pratt1985). Howquicklythefootisbroughttoahaltandhencethepeakdecelerationexperiencedisdependent uponthehorizontalshearcharacteristicsofthesurface.asinthecaseoftheverticalloading,arapid decelerationincreasestheriskofexcessivestrainandtherateofstrainapplicationandthusthe potentialinjurytotheleg(johnstonetal.1994).ifthereisapartialshearfailureofthetrackmaterialas thehoofisbroughttorest(i.e.thereissomeslippageofparticlesacrossoneanother),thedeceleration willoccuroveralongertime,reducingthemagnitudeofthedeceleration.thesebrakingshear requirementsmustbebalancedwiththoserequiredforforwardpropulsionafterthemid stancepoint. Optimally,itisexpectedthatthesurfacewouldallowsomeslideduringtheinitialimpact.However, onceloadedverticallybytheweightofthehorse,thesurfacewouldprovideadequatecarryingcapacity andshearresistancetosupportthehoofwithoutfailureduringthepropulsivephase(petersonetal. 2008).Iftheshearresistanceislow,itissometimesreferredtoasatrackcuppingout,sincethehoof willslideandelongatethehoofprintduringpropulsion.duringbreakover,thesurfaceresistanceto sheardeterminestheextentofhoofrotation(cheneyetal.1973,zebarthandsheard1985).thehoof rotatesgraduallyintoalowshearstrengthsurfacesuchassandduringtheloading,compensatingfor thechangingdirectionofforce(riemersmaetal.1996,hoodetal.2001).thelowshearstrengthofa sandsurfacethusalterstheloadingofthejointsandtendonsofthedistallimbduringmaximalloading ofthesestructures(chateauetal.2006,spännaretal.2004).theloadingofthesestructureswhile influencedbythefooting,isalsohighlydependentonindividualbiomechanics.conformationofthe horseisveryimportant,sinceitwillinfluencetheanglesandloadsonthesupportingstructures.in addition,otherfactorssuchasshoeingandeventrainingmayinfluencejointloading. Inadditiontothesemechanicalproperties,rough,deformablesurfacesincreasethevariance bothoftheverticalforcesatthehoofandofthepositioningoftheloadinthehoof(kaietal.1999). Therefore,itiscriticaltounderstandboththeidealsurfacepropertiesandthemaintenancethatis requiredtosustainthem.aproperlypreparedtrackthatisuniformthroughoutitscourseshould positivelyinfluencetheperformanceandorthopaedichealthofthehorse. 8

11 TYPES OF RACING SURFACES Design Todate,littleformaldiscussionhasbeengiventodesignoftheracingsurface.Thedesignof racetrackshasgenerallybeenthepurviewofexpertswhohavedevelopedstrategiesthatare appropriatetoparticularclimatesandmaterials.however,becausetheapproachesofdifferentexperts whohavecontractedforspecificjobshavedifferedfromsitetosite,thisapproachhasresultedin drasticallydifferenttrackdesignsincloseproximitytoeachother.thisbeliestheclaimthatthedesign mustadapttolocalmaterialssinceverydifferentdesignsareoftenlocatedwithincloseproximity.the adaptabilityofthehorsehasallowedthistocontinue,butostensiblythesedifferentdesignsshouldhave advantageswithrespecttosafety,andifsafetyisnotsignificantlydifferentforthesesurfaces,thenease ofmaintenanceandotherconsiderationsmayresultinanoptimaldesignforalocation. Cushion and Base Perhapsthemostnotabledifferencebetweentypesofracingsurfacesistheconfigurationofthe cushion,thepad(whenapplicable)andthebase.threebasicconfigurationsofaracingsurfaceexist: 1.ashallowsandtrackwithasolidbase 2.asandandclaytrackwithapadthatismaintainedonaregularbasis 3.atrackwithadevelopedbasethathasashallowsandorsand and claytrackmaterial laidoverabasewhichisnotdisturbedonaregularbasis. Thesethreebasicdesignspredominateregardlessofthetypeofmaterialusedforthetrack. Traditionally,thedesignofthecushionandbasehasbeenassumedtodependontheclimateand materialsofaregion.however,numerousexamplesexistoftrackswithclosegeographicalproximity withdifferentdesigns,soitislikelythatthedesignofagiventrackisasdependentontheexperienceof thedesignerasitisontheclimateandmaterialusedinthetrack. Shallowsandtracksoverahardbasearetypicallyusedwithverylowclayandsiltcontent.The mechanicsofthehoofinteractionwiththistypeoftrackarecharacterizedbyahoofprintwhichisin verycloseproximitytothebaseduringnormalusage.thecushionistypicallyontheorderof3½to4½ inchesdeep,andthehoofprintduringbreakoverisnearlyincontactwiththebase.thelowclayandsilt contentresultsinatrackthatmustmaintainhighermoisturecontentinordertoretaintheeffectiveness ofthecushioningofthesandoverthehardbase.theseshallowsandtracksarealsotypicallyveryfast drainingandthuscanbeusedwhenheavyrainfalliscommon.whilerequiringhighmoisturecontentto retainthecushioningofthesurface,thetrackwillrapidlyrecoverfromheavyrainsincethesurfaceis permeableandthewaterwillflowbothacrossthetopofthecompactedtracksurfaceandthoughthe permeablematerialtowardthelowerelevationattheinsiderailofthetrack.thehardbasecanbe composedoflimestonescreenings,soilcementedsand,compactedclay,porousasphaltoreven concrete. Thesecondcommondesignofadirtracingsurfaceusesthesamematerialatadepthinthe trackthatgreatlyexceedsthedepthofthehoofprintinnormaloperation.inthistypeoftrack,a 9

12 materialthatissimilartothetopsurfacemayextendfrom8inchestoasdeepas24inchesabovethe basematerial.withinthistypeofdesign,twodistinctcategoriesexist:trackswithafalsebaseand trackswithamaintainedpad.trackswithafalsebasehaveashallowcushionjustliketheshallowsand tracksthatoverlayahardpanlayer,whichmaybeascompactedanddifficulttopenetrateasthe surfacesontheshallowsandtrack.thehardpanlayerisdevelopedthroughrepeatedharrowingofthe surfaceatthesamedepth.averyhighstressareaexistsundertheteethofaharrow,whichwill compactthematerialbelowtheteethveryeffectively.inareaswithheavyrainfall,thetopsurfacewill graduallylosefinematerialandwillcreateadistinctcushionoverthefalsebasecreatedasahardpan layer.repairoftheunevenportionsofthebasecanbesimplyhandledbyrototillingthematerial followedbyrepeatedharrowingofthesurfacetorecreatethehardpanlayer.thisisnotdoneona regularbasisbutcanbedoneafteraperiodwhenthetrackhasnotbeenusedorwhensomedamageto thetrackhasoccurredovertimefromracingandtrainingmaintenanceorbecauseaheavyrainfallhas washedoutthefinematerialinanarearesultinginaportionofthetrackwhichislessresistanttohoof penetrationandcannoteffectivelysupportthehorse. Thethirddesignisavariationoftheseconddesignofsurface.Asintheseconddesign,the materialisconsistenttoadepthmuchgreaterthanthepenetrationofthehoof,evenduringbreakover. Thisdesign,however,usesaregularlymaintainedpadunderthecushionofthetrack.Thepadisa partiallycompactedlayerthatistypicallymixedoneormoretimesperweektomaintainalevelof complianceinthelayerbelowthecushion.typicallythispartiallycompactedlayeris2to4inchesthick. Thehardpanlayerthatdevelopsbelowtheharrowteethisintentionallydisturbedduringaweekly maintenanceprocedureconsistingofbreakingandmixingofthelayers.thecompositionofthistypeof dirttrackisdifferentfromthatofotherdirttracks,sinceittypicallyhasclayorothercohesivematerial. Mostofthewax basedsyntheticracingsurfacesarealsomaintainedinthisfashion.thehighclay contentdirttracksaremostcommonindrierclimateswherethetrackcanbeoperatedwithlower moisturecontent,whileretainingthesupportrequiredforthepropulsivephaseofthegait. Thedistinctionsbetweenthetypesoftrackarelessclearinturftracks.Becauseoftheneedto maintainagrowingmediumthroughouttherootzone,aturftrackisgenerallyhomogeneous throughouttheentiredepthoftheportionofthetrackthatthehoofcontacts.aturftrackalsouses aerationandothermechanicalmeanstomaintainasoftertoplayerandtoopenupthesurfaceto increasepermeabilitytotherootzoneandtohelpmaintainthecomplianttopsurfacewhichisneeded toreducethepeakloadonthelegofthehorse.theturffoliageandthatchlayersarebiomechanically analogoustotheharrowedcushiononadirttrack.thissurfaceanditsassociatedrootstructure overlaysthesoil,whichwillberelativelyhomogeneousduetothemaintenanceneedsassociatedwitha healthyturflayer.aprimarydistinctionbetweenturftracksandtypesofturfwillbethedegreeof compactionofthegrowingmediumandthestrengthoftheassociatedrootsystem,whichwillaffect boththehardnessandtheshearstrengthofthesoil.ingeneralthough,choiceofmaterialsthatresist compactionandtheuseofmechanicalmethodstoreducecompactionwillresultinsurfacesthatclosely resemblethedirttrackswithapadintheirmechanicalperformance.theconsistencyofthe maintenanceprotocolforthistypeofsurfacecanbeclearlyseenfromtheconditionoftheturfgrowth. 10

13 Belowthemaintainedlayersofsand,orsandandclay,orturf,theprimaryfunctionofthebase istocreateaconsistentlevelsurface.theroleofabasethatismorethan12inchesbelowthetop surfaceofthetrackislesscritical.inthosecases,maintenanceofthepadorfalsebaseisofprimary importance.however,aconsistentbaseisstillanimportantfactor,sinceitcanbeimportantfor drainageandcanprovideastablelayerforinstallationandheavymaintenanceofthetrack.forshallow sandtracks,thebaseiscriticaltomaintainingasafesurface.sincethetoeoftheshoewillbecloseto thebase,andthebaseprovidesasignificantpercentageofthesupportrequiredforthehoofduringthe loadingphase. Geometrical Configuration Whiletherehasbeenlittlecomparativeresearchonthedifferentdesignsofsurfacesof racetracks,slightlymoreconsiderationhasbeengiventothegeometricalconfigurationofaracing surface.however,mostoftherigorousandsystematicworkhasbeendonewithtrottinghorsesrather thanwiththoroughbreds.understandingthemethodsofdescribingthegeometryofaracetrackis criticaltounderstandingrisktothehorseandrider.typicalareasofinterestincludetheslopeand possibleexistenceofacrownonthestraights;thelengthofthestraightsrelativetotheturns;the bankingorsuper elevationoftheturns;andtheradiusoftheturnsandwhethertheradiusoftheturnis constantorvariesthroughtheturn. Ondirtorothersurfaceswherewaterisshedacrossthesurface,evenstraightsectionsofthe trackwillslopetowardtheinsiderail.whilesometrackshaveaslittleas1%grade,thetypicalgrade towardtheinsiderailismorethan2%.thisallowsthetopsurfaceofthetracktobecompactedwitha floatsothatrainwilldraintotheinsiderail.onwidertracks,acrownisusedsothattheoutsideone quarteroronethirdofthetrackwilldraintotheoutsiderail.whilehardertomaintain,thiscrowningof thetrackreducestheamountofwaterthatmustbemanagedontheinsiderailand,dependingonthe trackmaterial,canreducelossoffinematerialontheinsiderail.thebiomechanicalimpactofrunning onaslopedsurfacehasnotbeenstudiedsystematically.thecommonasymmetryoftheridingposition (acey deucy)withtheleftstirruplowerthantheright,whichistypicallyusedforracingthoroughbreds, furtherexacerbatesasymmetryofloadingontheanimal.incontrast,mostsyntheticracingsurfaces dependonverticaldrainageandmayhaveflatstraightsectionsandmoreflexibilityinthebankingused inthecorners.theimpactofthebankinginturnshasbeenthesubjectofalargeamountofdiscussion butonlyasmallamountofsystematicevaluation.thebestunderstandingoftheissuestobe consideredisinsomearticlesoutsideofthescientificliterature(coons1981).however,thisworkis basedonengineeringconceptsusedinroadbuildingratherthanbiomechanics.inthisandother articles,thedefinitionsandconceptsthatarewellestablishedfromroadandrailroadbuildingare appliedtohorseracing.inparticular,thespiralturnisdefinedandtheapplicabilitytohorseracingis discussed.developingtruespiralturnsinthecurrentracetrackswouldbequitedifficultbecauseofthe requiredchangesinthegeometryofthetrackandthelimitedspacesurroundingmostracetracks. WhileThoroughbredracinghasbeenthesubjectofdiscussionoftheissuestobeconsidered, previousworkwithbankinghasneverlinkedthistoloadingonthelegs.thisisacomplexissuefor thoroughbredsbecausethehorsehasanabilitytoleanintothecornerandtheasymmetricriding positionofthejockeyreduceslateralloadingonthelegsintheturns,whileincreasinglateralloadingin 11

14 thestraights.thesefactorscombinetomakebankingoptimizationspecifictonotonlythespeedand radius,butalsotothepositioningofthejockeyandthegaitofthehorse.themostimportantwork linkedtothebiomechanicsofthegaitandrisktothehorsehasbeendonewithtrottinghorses,andit specificallylinksbankingwithinjuries(fredricsonetal.1975).thisworkhasbeenrepeatedinother racingjurisdictions,butalsowithstandardbredhorses(evansandwalsh1997).nocomparablestudy hasbeenperformedwiththoroughbredhorseswiththedifferencesinloadingandgait,whichmakes extrapolationoftheresultsfromstandardbredhorsesproblematic.thereis,therefore,aneedto understandtheoptimaldesignofaracetrackandtounderstandtheimplicationsofthecurrentdesign forthehealthofthehorse. Composition and Design Nootheraspectofracingisasfirmlyestablishedascharacterizingtheuseofbasiccomposition measurements.atleastabasiccompositiontestisusedatnearlyallracingvenuesandisakeyaspect ofmanagementofthesurface.lesswellunderstoodistheinteractionoftrackdesignandcomposition. Thetypeofmeasurements,frequencyandlocationsforsamplingaredifferentforashallowsandtrack laid over a hard base than for the other track designs. In contrast, surfaces that can be effectively compactedarewellsuitedtobasematerialsandforuseintracksthathaveafalsebaseofcompacted material. Better quantitative methods of characterizing track material are needed. In addition, new developmentsfromsynthetictrackmaterialcharacterizationmustbeextendedtothetestingofdirtand turf track materials, and these characteristics must be linked to the climate and design of particular tracks. TESTING OF RACING SURFACES Surface Material Characterization Thecharacterizationoftheracingsurfacematerialsisthebestunderstoodandmostcommon typeofracingsurfacemonitoring.whileimportanttotheoverallperformanceofthesurface,material isjustoneaspectofdevelopinganappropriateracingortrainingsurface.manyofthediscussionswhich revolvearoundthesurfacematerial,arereallyissuesassociatedwithweatherormaintenance. However,withoutconsistentandappropriatematerial,itcanbedifficultifnotimpossibletohavea goodracingsurface. Composition Testing Mosttracksusesimplesieveandhydrometertesting(ASTMD422,2007)todeterminethesand particlessizeandpercentageofclayandsilt.thebest establishedcharacteristicofthesievedataisthe correlationbetweenbroadparticlesizedistributionandthecompactabilityofthematerial.however,a numberofothercharacteristicsofthesieveandhydrometerdataarelesswellestablished,suchas relativepercentagesofclayandsiltandtheeffectoffinematerialmixedinwithcoarsersand.serious concernshavealsoarisenregardingthesuitabilityofthetraditionalhydrometertestingforthe determinationofclaycontent(luetal.2000),whichisacriticalfactorinthedesignoftracksinmore aridregions.inaddition,theintroductionofsyntheticsurfacesinnorthamericawasnotinitially accompaniedbyextensivenewmethods,butsomepartsoftheindustryhaveworkedtodevelopthese methodsasthesurfaceshavebeeninuseovertime.ingeneral,compositiontestingisusefulfor 12

15 maintainingdesirablepropertiesofasurfacethathasbeenfoundtowork.thesimplecompositiontests mustinthecaseoftraditionaldirtsurfacesbesupplementedwithtestssuchasclaymineralogy,andin thecaseofsyntheticsurfaces,fullthermo mechanicalandchemicalcharacterizationofthewaxis requiredtomaintainthepropertiesofthesurface.however,beyondthedetailsofsieveandgas chromatographyisthebigpictureofmaterialresponse. Perhapsthemostimportantcharacteristicofallthecushionsurfacesistheshearstrengthofthe material.shearstrengthisafunctionofthecohesionofthematerialandtheshear.thecohesionof thematerialisaresultofbondingbetweenthesandparticles,whichistypicallyinfluencedbyclayindirt surfaces(al Shayea2001)andwaxinsyntheticsurfaces(Bridgeetal.2010a).Inaddition,friction betweenparticlescanbeenhancedbythepresenceoffibersorrootsthatcanfurtherincreasetheshear strength.thefrictionalportionoftheshearstrengthincreasesastheloadonthematerialincreases. Therefore,inordertounderstandachangeintheshearstrengthofasurface,itisnecessaryto understandthedetailsoftheshapeandsizeofthesand,aswellastounderstandtheexactnatureof thecomponentsthatincreasetheshearandcohesion,suchasfibercontent,claymineralogyandwax chemistry.thebasictestsfordirtandsyntheticsurfacesareshownbelow: DirtTracks Sieve separation Hydrometer tests of clay and silt Organic content Bulk density (as a function of moisture) Salt content X-ray diffraction for clay mineralogy Sand microscopy SyntheticTracks Wax percentage Fiber and rubber separation Gas chromatography of wax Differential scanning calorimetry of wax Oil content measurement Bulk density (as a function of moisture) Sand weight percentage Sand particle size distribution Moisture holding capability Laboratory Performance Testing Compositiontestinghasthedistinctlimitationthatitonlydescribesthematerial,nottheresults whichoccurfromthecompositionofthematerial.forsurfacesthatmayhaveuniquelocalsandorclay, thisisparticularlyproblematic,sincetheperformanceofthetrackmaynotbeconsistentwithother sandandclaytracks.asaresult,laboratoryperformancetestingisneededbothtoevaluatethe performanceofthecomponentsofthetrackmaterialandtodetermineifthecompositionproduces 13

16 valuessimilartootherracingsurfaces.inaddition,in situperformancetestingshouldbeusedto describetheoverallperformanceofthematerialwhencombinedwiththedesignofthetrack. ShearStrength:Theshearstrengthofthecushionmaterialisthemostfundamentalcharacteristicof theperformanceofthetrack.amaterialwithhighcohesionwillreducetheslideduringtheimpact phaseofthegait;lowshearstrengthwillkeepthetrackfromsupportingthehoofduringthepropulsion phaseofthegaitresultingincuppingout.finally,duringbreakoveronmanymaterials,thetoeofthe hoofwillpenetrateintothetrack,whichisalsocharacterizedbytheshearstrengthofthematerial. Figure3showstheconfigurationofthetestcellusedfortheshearstrengthtestingwhichisbasedona standardtestmethod(astmd4767,2004).inthecaseoftraditionalmaterials,thetestingisdoneata rangeofmoisturecontents,whereasthetrackmaterialtemperatureiscontrolledforthesynthetic materials. Figure3:Configurationofthetriaxialtestcellusedforthedeterminingthetriaxialshearstrengthof trackcushionmaterials Inthetriaxialshear,thetestisperformedusingacylinderofthetestmaterialthatissurrounded byapressurizedfluid.thetopofthecylindricaltestspecimenisloaded,andthedeflectionofthe sampleismeasured.thepointatwhichthesamplebeginstofailistheshearstrengthataparticular confiningpressure.thetestisrepeatedforarangeofconfiningpressurestoevaluatethecohesion(the strengthwithzeroload)aswellastodeterminetherelationshipbetweenincreasedloadingandthe shearstrengthofthematerial.typically,twelveto15testsareperformedtounderstandtheeffectof moistureortemperatureonthecohesionandthefrictionalcomponentsoftheshearstrength.thelink betweenthesemeasurementsandkeyaspectsofthewaxcompositionhasbeendemonstratedfor materialsfromanumberofdifferentsyntheticracingsurfaces(bridgeetal.2010,bridgeetal.2010a). Compaction:Thecompactabilityofthesurfacematerialdeterminesboththeeffectofhorsetraffic betweenmaintenanceofthematerialaswellastheabilityofamaterialtoformasolidbaseunderthe 14

17 track.thesetwogoalsaresomewhatcontradictoryforatrackwherethetopmaterialandthebaseare thesamecomposition.forexample,theidealtrackwouldhavelimiteddifferencesinthesurface regardlessoftheamountofhorsetrafficthathadpassedacrossit.however,agoodbasematerial shouldbeeasytocompact.thisisaddressedinshallowsandtracksbyusingadifferentmaterialforthe baseandthecushion.however,thismeansthatundersomecircumstancesthehorsesmayendup runningonaveryhardsurface,somaintenanceofthebasebecomescritical.ifapartiallycompacted padisused,thenabalanceshouldbemaintainedbetweenconsistencyofthesurfaceandproviding cushioningforthehoof.thecompactionofthesurfaceisafunctionofthemoisturecontentofthe materialwithmaximumcompactionoccurringatparticularmoisturecontent.amodificationofa standardtestisusedthatallowsareasonableamountofmaterialtobeusedfortesting(astmd ,Dı az Zoritaetal.2001).Fromthetests,agraphicalcurverelatingmoisturecontentversusbulk densityisproduced.thisinformationprovidesguidanceregardingtheoptimalamountofmoisturetobe addedtothebasematerialtoallowittobeeffectivelycompacted.thecompactioncurvealsohelpsin understandingtheeffectsofmoistureonthetrackwhenthecushionissealedpriortorainorotherwise maintainingthetrack. ImpactAbsorptionandEnergyReturn:Themannerinwhichenergyisabsorbedinthetrackmaterial hasnotbeenpreviouslyinvestigatedandmustbebetterunderstoodtodevelopasystemthattracks boththesafetyandspeedofsurfaces.ingeneral,fromthehumanliteratureitisknownthatdeepand absorbingsurfacesaretiringandmaybeassociatedwithparticulartypesofinjuries(kerdoketal.2002, Barrettetal.1997).Atthesametime,itisclearthatthepropertuningofasurfaceforhumanscan resultinbothafastandasafesurface(mcmahonandgreene,1979).understandingthesedynamics forhorseracingcanbedonetoacertaindegreewithlabtestsbutislikelytoalsoinvolvethedesignof thesurfaceandthuswillprobablyrequirein situmeasurements.theimpactabsorptionduringthe initialimpactstageisafunctionofthedynamicresponseofthehooforthehardnessoftheimpactor,as wellasthemodulusofthesurface(referredtoasthetargetinimpactmechanics)(abrate1994, Goldsmith2001).Thissameeffecthasbeenclearlyobservedinmeasurementsonhorseswherethe effectofsurfacesisrelatedinacomplexfashiontotheanatomyofthehoof(burn,2006).atthistime nostandardtestisavailable,butthepotentialexistsfortestsdevelopedforotherpurposestobeused tocharacterizetheenergyreturnandtheimpactabsorptionofthesurfaces(astmd3763,2010). However,aswiththetriaxialandothertests,thetestwillneedtoberunwithcarefulcontrolofthe moisturecontentandtemperaturefordirtandsyntheticsurfacesrespectively.likemostofthe laboratoryperformancetests,thesetestsarepoorlysuitedtoturftracksandareprimarilyapplicableto dirtandsyntheticsurfaces. MoistureSensitivity:Forbothdirtandturfsurfacesthereisaneedtounderstandtherelationship betweenthewatercontentandthesurfaceperformance.forthesesurfaces,moistureisthesingle mostimportantvariableinthemaintenanceofthesurface.forshallowsandsurfaces,aspectsofthe trackdesignsuchasthetypeandconsistencyofthedrainagealongtheinsiderailisalsoimportant.for turfsurfaces,thewetabilityofthematerialandthedesignandmaintenanceoftheirrigationsystemare criticalissues.assyntheticsurfaceswear,itisalsolikelythatthesensitivitytomoisturewillincreaseas thehydrophobiccoatingislostfromthesurface.therelationshipbetweenmoisturecontentandshear 15

18 strengthiswellestablished(al Shayea,2001),evenformaterialssimilartothoseusedinracingsurfaces (Ratzlaffetal.1997).Ingeneral,theshearstrength,likethecompactability,reachesamaximumata particularwatercontentwithlowershearstrengthatbothlowerandhighermoisturecontents. However,thepercentageofmoistureatwhichthemaximumoccursishighlydependentonthe material.further,thesensitivityofthemoisturecontentaroundthepeakisalsohighlymaterial dependent.thesecharacteristicsmustbedevelopedforeachmaterialandthenmonitoredforchange overtime.theuseofthetriaxialsheartestasafunctionofmoisturecontentisusefulfordirttrack materialmuchasithasbeenusedforsyntheticsurfacematerials(bridgeetal.2010). Permeabilitymustalsobeconsiderediftheflowofwaterthoughthesurfaceisanimportant aspectofthedesignofthesurface.again,thepermeabilitycanbemeasuredusingstandardtest methods(astmd5856,2007).forsyntheticracingsurfacesandturftracks,thewatermustbeableto penetratethesurfacefordrainageandforturfhealth.mostsandtracksdonothavesignificant permeabilitythroughthedepth.however,onthesesurfacesaportionofthedrainagetowardtherail mayoccurwithinthetracksurface,andamorepermeabletrackwillquicklyrecoverfromrainandwill bemoredifficulttokeepwetduringdryperiods.generally,withtheexceptionofthedrainagetoward therailforshallowsandtracks,permeabilityofthesurfaceisnotamajorfactorfordirtracingtracks, sincethesurfaceissealedbeforerain,andtheprimaryflowofwaterisacrossthetopofthetrack towardtherail. In-Situ Testing Regardlessoftheutilityofthelaboratorytests,thesetestsareessentiallylimitedtoensuring thatatrackstaysthesameovertime.inadditiontotheselaboratorymeasurements,theconsistencyof thetrackisdeterminedbyhowthedesignisimplementedandbyhoweffectivethemaintenanceisin keepingaconsistentsurfacethatiswithintheoriginaldesignparameters.however,eventhese measurementsarenotacompletepictureofthetrack.thecomplexinteractionofclimate, maintenance,usage,anddesignoccursonlyattheracetrackwhereallaspectsofthesurfaceinteractto providearacingsurfaceforthehorses.understandingacompleteinteractionofthesefactorsrequires in situperformancemeasurementsthatdonotpresupposeaparticulartrackdesign.in situ performancemeasurementscanbequitecomplex.furthermore,itisclearfromlookingatdifferent designsindifferentlocations,thatasinglesolutionisnotpossibleandthatatrackdesignwhichworksin onelocationmaynotbeidealinallapplications.therefore,eventuallyonlyperformancemeasurements thatdonotpresupposethedesignofthesurfacecanbeusedforevaluatingthecharacteristicsofa racingsurface. Operational Measurements Basicoperationalmeasurementsofthesurfacedependonthedesignofthesurfaceandthe climate.veryfewracetrackshaveasystematicapproachtothesemeasurements,eventhoughtheyare criticaltomaintainingaconsistentsurface.thesebasicmeasurementshavethepotentialto significantlyimprovetheconsistencyofracingsurfacesatthosetracksthatdonotcurrentlyperform thesemeasurements.caremustbetakentomakethemeasurementsinamannerconsistentwiththe typeofsurface. 16

19 MoistureContent:Thesinglemostimportantvariableondirtorturfsurfacesismoisturecontent.For turfsurfaces,themoisturecontentofthesurfacebothcontrolshealthoftheturfandthemechanical propertiesofthesurface.fordirtsurfaces,themechanicalpropertiesareafunctionofthemoisture contentandcanvarydramaticallywithevensmallchangesinmoisturecontent,dependingonthe material.moistureischallengingsinceitcanchangedramaticallyoverashorttime.inashallowsand track,thebiggestchallengeisgettingenoughwateronthetrackduringadryperiod,sincemanyof thesetrackscantakealotofrainfallandwillshedthewaterveryeffectively.ontracksthatarecapable ofoperatingeffectivelyduringdryperiods,thechallengeistokeepenoughwateronthetrackto maintaintheshearstrengthandtomanagethetrackduringperiodsofrain.twoseparatefactorsneed tobeaddressed:variationofmoistureoverthetotaltrackbetweendays,andvariationinthemoisture contentaroundthetrackor,moreformally,thetemporalandspatialvariationofthemoisturecontent ofthetrack. Inordertocompleteaspatialmaptomonitorthevariationinmoisturecontentaroundthe track,asimple,fastreadingprobeisneeded.thisisnotsimpleforaracetrackbecauseracingsurfaces operateoverawiderrangeofmoisturecontentsthanseeninmosttypesofagriculture.also,onatrack whichexperiencesheavyrain,thesaltandclaycompositioncanchangeovertimeaswaterpasses throughthesurface.bothsaltandclaycompositionwillaffectthemoisturereadingsfrommost moistureprobes.thebestprobefortheconditionsoftheracingsurfaceisatimedomain Reflectometry(TDR)probe.TheTDRprobeisaffectedbybothsaltandclaybutcanbecalibrated,andit effectivelyaveragesthroughthedepthofthecushionofthetrack.severaldevicesareavailable,anda numberofcompaniessellthesameunit.theseunitsarealsoavailableinaconfigurationthatallows themtobeusedwithalowcostcommercialgpssystem.currentlythecommunicationtothegpsisnot reliableandisnotworththebotheruntilthecommunicationwiththegpsbecomesmorereliable. WithouttheGPS,datacanbeeitherwrittendownordownloadedtoacomputerandmanuallymapped. Typicallyitisbestifthemoisturecontentofthetrackismappedaftertrainingandafterracing. Thisgivesanideaofwetanddryspotsandcanbesharedwiththemaintenanceteamtoidentify approachesthatcanbeusedtoavoidwetanddryspots.inparticular,attentioncanbebroughtto issueswithtrackdrainage,shadingofthetrackfromfoliageandthegrandstand,andoverwateringthe insideoftheturnsduetotheshorterdistancetraveledbytheinsidenozzleonthetruck. Temporalmoisturemeasurementismoredifficultbecausetheweathercanchangeduring trainingandracing,andthisshouldbeconsideredinthewaterapplicationandothermaintenancesuch asfloatingofthetrack.mostexperiencedsuperintendentsaregoodatobservingthesechangesand respondinginrealtimeespeciallytorainfall.evaporationismuchmoredifficult.insomecases,the evaporationrateisevidentfromthecolorofthetrack,butalightsprayofwateronthetopcanmaska graduallydryingtrack.inprecisionframingthisishandledwithevapo transpirationmodels.theseare modelsthatdescribethelossofwaterfromtheleavesandsoilinfarming.usingaspeciallydesigned weatherstation,theseevapo transpirationmodelscanguidefarmersintheirrigationofcrops.while horseracingissimilar,themodelsdonotworkforthemaintrack.sincethetrackisharrowedbetween racesanddoesnothavecropcover,theevaporationrateforthedirtismuchhigher.whileacademic workhasaddressedsomeoftheissueswithevaporationfromharroweddirtsurfaces,thesemodels 17

20 havenotbeenimplementedfortheuniqueconditionsofhorseracing(stroosnijder1987,mutzigeretal. 2005).Factorssuchasthedepthoftheharrowneedtobeaddedtothemodelfortheracingsurface weatherstation.thesemodelsdonotcurrentlyexist,butweatherstationsthathavebeendeveloped forprecisionagriculturecanbeadaptedforuseontheracetrack. Depth:Depthofthecushionisacriticalandrelativelystraightforwardmeasurementonshallowsand tracksurfaces.requiringnothingmorethanamarkedprobe,thesurfaceonashallowsandtrackcanbe probedregularlyatevenlyspacedintervalstoensurethataconsistentamountofcushioncoversthe hardbase.thiscanalsobedoneatmorecloselyspacedintervalsandwithhigheraccuracyusingground penetratingradar.thebestcaseisacombinationofregularprobingofareaswithknownissuesand periodicevaluationwithradartoensurethattheoverallsurfaceconsistencyisgood. Fortrackswithapadorfalsebasedesign,thedepthisamorecomplexcharacteristic.For surfaceswithafalsebase,thedepthofthecushionusuallyisreferencedtothetopofthetrack,andas longasthebaseisfirmcanbemeasuredinthesamemanneraswithashallowsandtrack.however,if thebaseisnotwelldevelopedorifapadisused,judgmentisrequiredtodetermineifthecushionisthe samedepth.inthatcase,therelevantdepthisbasedonthedepthofthematerialafterperiodic rototillingandonanassumptionofaccurategradesonthesurfacesofthetrack.alternatively,ground penetratingradarcaninmanycasesbeusedtoshowthedepthofthecushionandthedepthofthepad ifthedifferenceinthedensityofthematerialissufficient. MaterialConsistency:Oneofthecontinuingchallengesforsurfacesisdifferencesinwearand movementofmaterialinthesurface.foraturftrack,thisismitigatedbymovingtheinsiderailonthe trackandspreadingoutthewearonthesurface.however,fordirtandsyntheticsurfacesthisisnot done.severalfactorswillalterthematerialcompositionacrossthewidthofthetrack,includingheavy horsetrafficalongtherail,lossoffinematerialalongtherailtothedrainagesystem,drainagefrom chutesacrossthemainovalofthetrack,andphysicalmovementofmaterialduetothebankingofthe turns.aroundthetrackvariationinthecompositioncanalsooccurduetomovementofequipmentand horsesontothetrack,moreheavilytraffickedportionofthetrackfromthe6furlongpoletothewire, andtrafficonthetrackunrelatedtoracing.inbothcasesmeasurementsareneededthatcanbeusedto comparethetrackontheinsiderailwithmaterialfurtheroutfromtheracingsurface.sampling protocolsforlaboratorytestingcanincludesamplesfromlocationsthataretwodistancesoutfromthe railaswellassamplingfromlocationswithknownissuessuchastheclosetotherailonthetrackwhere waterfromthechutewillflowtowardthedrainagesystem.themostbasicsamplingprotocolusedis formaterialtobetakenfromthetrackatthe⅛,½and¾polesatalocation2metersfromtherail, alongwithtwosamplesatthewireandthe¼poletakenatdistancesof1meterand3metersfromthe rail.thissamplingmethodgivesinsightintothevariationofthematerialattwodistancesfromtherail aswellasprovinginsightintoanyvariabilityaroundthetrack. Temperature:Forsyntheticsurfacesthatoperatewithminimalmaintenanceandhavenotworn significantly,temperatureessentiallytakestheplaceofmoistureforturfanddirttracksinthediscussion ofkeyvariablesforthesurface.withpropermaintenance,thiseffectcanbemoderatedifnot 18

21 completelyeliminated.liketheeffectofmoisture,theeffectoftemperatureisnotsimplylinearbutwill resultinmaximumvaluesfortheshearstrengthaswellasothereffectssuchashighcohesionofthe materialleadinguptoballingofthematerialinthefrog.monitoringtheeffectoftemperatureonthe surfaceallowstheuseofmaintenancemethodssuchasharrowdepthvariationandtheadditionof watertoreducetheseeffects. Geometry:Asdiscussedabove,thegeometryoftheracetrackincludingtheradiusoftheturns, banking,andtransitionsfromthestraighttothebankedturnshavebeendemonstratedtobeimportant instandardbredracing.whilescientificevidencedoesnotexisttodemonstratetheoptimaldesignof theturnforathoroughbred,logicsuggeststhatthetransitionsshouldbesmoothandconsistent. Epidemiologicalworksuggeststhatthegeometryoftheturnswouldbeconsideredasapossiblesource ofriskforthehorse.thusitisimportanttoconsistentlymeasurethebankingandtoensurethatthe transitionsaremaintained.thiscanbedonewithlaserorgps,andthepositionscanbeeither programmeddirectlyintoagpscontrolledgraderorcanbebasedonmonumentsplacedonthe perimeterofthetrackforreferencepurposes.thistechnologyiswellestablished;however,the precisionrequiredforhorseracingsurfacesismuchhigherthanthatofmanyapplicationsandthus suggeststhatcarebetakenwhenusingoff the shelftechnology. In-situ Performance Testing Regardlessofhowcarefullythevariousaspectsofracetrackdesignandmaintenanceare performed,thesefactorsmustbecombinedintherealworldtoproduceconsistentresults.these resultscanonlybemeasuredin situsothatthecombinedaspectsofthesurfacecharacteristicscanbe understood.theidealmeasurementmethodwouldreplicatethehorsemovingonthesurface.direct measurementsofpeopleorhorsesarenottypicallyusedtocharacterizethesurfacebecauseof individualvariationingaitandotherfactorssuchasfatigueorinjury(shorten,2008).inaddition, testingtheinteractionofspecifichorseswithspecifictractconfigurationscanbecomplexandexpensive forananimalthesizeandspeedofaracehorse.therefore,theotheroptionsforin situtestingoftracks shouldalsobeconsidered. SimpleIn SituTestingDevices:Severalsimpledeviceshavebeenproposedforthetestingofracing surfacesandsomeofthesedevicesarecurrentlyinuse,suchastheclegghammer,thedynamic penetrometer,andtheagriculturalpenetrometer.however,withoneexception,thesedeviceshave beenadaptedfromotherapplicationsandtypicallyrequireasignificantamountoftechniqueinorderto producerepeatableresults.thelongtermgoalshouldbetodevelopmonitoringmethodsthatcanbe consistentlyappliedandwhichcannotbeeasilyinfluencedbytheoperator. TheCleggHammerisprobablythemostcommonlyusedmeasureofsurfaceperformancein NorthAmerica.TheCleggHammerwasdevelopedprimarilyforlookingatthecompactionofbase courselayersforroadways.becauseoftheinitialuseofanalogelectronicsintheearlysystem,onlythe peakaccelerationwasdisplayedontheunit.thepeakaccelerationafterfourimpactsofthemasson thesurfacewasusedinthisunittoreplicatetheeffectofequipmentusedtocompactsurfacesover whicharoadwaywouldbeconstructed.asignificantbodyofworkexistsintheliteraturethatrelated theclegghammerreadingstoparametersofinterest,includingsomemorerecentworkthateven 19

22 proposesthereplacementofthenucleardensitymeterforsomeapplications(farrag2006).theclegg hammerhasbeenshowninthisworkaswellasothereffortstobecapableofmeasuringthe compactabilityofasurfaceifthemoisturecontentisalsomeasured.clearly,however,the compactabilityrequiresthatthemoisturecontentbemeasuredaswell,sincethemoisturecontenthas afirstordereffectonthecompactionofmaterials(al Shayea2001,Ohuetal.1989,andothers). Thistypeofmeasurementisusefulforracingsurfacesfortheevaluationoftheconditionofthe baseandinmeasurementsthatmatchthosethatarerelevanttoroadbuilding.ifthemaximum compactabilityofasurfaceisimportant,suchaswiththosesurfacesthatdependonafalsebaseor hardpanlayertosupportthecushion,thentheclegghammerisausefultoolfordeterminationofthis characteristicofthesurface.inthisapplicationthecushionshouldbescrapedawayfromanareaofthe trackandthepadorfalsebaseshouldbetested.byusingtheaverageandmaximumvaluesthecurrent andpotentialcompactionofthepadorfalsebasecanbedetermined.theclegghammer,however, doesnotprovideusefulinformationregardingthepeakloadonthehoofbecauseofthesmallweight andtherepeatedimpactonasurface.therepeatedimpactofthesurfacewiththeclegghammer, whichisnecessaryforinfluencingthesurfacebelowthetopcushion,eliminatestheinfluenceofthetop harrowedlayerontheloadingofthehoof.iftheinitialdropisevaluated,themeasurementdoesnot includeanythingexceptthetopcushionlayer.thestandardclegghammeris2.25kg,whichmeansthat atthemodestheightfromwhichitisdropped,itunderestimatestheloadingonthesurfacefroma runninghumanoracanine.ultimately,theclegghammermayhavelimitedusesoutsideof compactabilitymeasurementsforcivilengineeringapplications,asrelevantstudiesinballsportsand humanathleticshaverecentlybeguntocastdoubtonthesimpleanalysisusedwiththeclegghammer electronicsforcharacterizingsportssurfaces(carréandhaake2004).indeedtheclegghammer measurementisnotapartofthestandardsusedfortennis,soccer,orothersports.instead,systemsof measurementthataremorecloselybasedonthebiomechanicalmotionofinterestarepreferredovera simpletestliketheclegghammer,whichiseasytoperform,butwhichyieldsone dimensionaldata. (BarryandMilburn2000andCawleyetal.2003). Thedynamicpenetrometeristhemostwidelyusedtoolforthecharacterizingofracingsurfaces. ThisdeviceismadebyGillEngineeringinAustraliaamongothercompanies.Unlikethebluntweightof theclegghammer,thisdevicepenetratesthesurfacewithasmalltoolsurfacethatmeasuresthedepth ofpenetrationintothesurface.thedynamicpenetrometerhasbeenusedprimarilyinareaswhereturf racingoverwhelminglypredominates.thisisbecausethistypeofdevicepresupposesthattothedepth ofpenetrationintothesurface,thesurfaceishomogeneous.thestronglayeringcommoninanytypeof dirtandmostsyntheticsurfaceswillmeanthatthecharacteristicsofrecentmaintenancewillcontrolthe depthofpenetration.however,forthetypesofhomogeneoussurfacesthatarepreferredforturf healthandforcertainaspectsofsurfacedesign,thisisawell establishedtool,whichissupportedinthe literature(murphyetal.1996).however,itisnecessarytocorrectthesemeasurementsforsoiltype andmoistureinordertocreateusefuldatathatwillhelptoprovideanunderstandingofthe performanceofahorseonasurface.theweightofthedeviceissmallandthemeasurementprobably relatesmostcloselytotheresponseofthesurfacetothehoofduringbreakover.modelingofthe 20

23 surfaceinteractionofthepenetrometermakesitpossibletocreateageneralratingofturfconditions thatcanbecomparedbetweenlocations(thomasetal.1996). Theprimarylimitationstothedynamicpenetrometeraretheinabilitytodealeffectivelywitha layeredsurface,suchasmostdirtandsyntheticracingsurfaces.littlediscussionhasalsooccurred regardingtheapplicabilityofthetooltosomewarmweathergrassesthatcancreatealayeredroot zone.theexistenceofahorizontalrootsystemandperhapseventheexistenceofreinforcingfibersor gridsinthesurfacecanresultinerroneousandhighlyvariablereadingsfromthepenetrometer.in general,thecharacteristiclengthofanyoftheconstituentmaterialsinthesurfaceshouldbeseveral timessmallerthanthemeasurementdevice.forexample,turfgridsthatareofthesamesizeasthe penetratingprobeofthepenetrometerwillresultinameasurementoftheexistenceorabsenceofa turfgridundertheprobe,notameasurementofthestrengthofthesoil.however,recognizingthe limitationsofthemeasurementandassumingpropercalibrationofthepenetrometertothesoiltype, alongwithsimultaneousmeasurementofmoisture,thedynamicpenetrometerisagoodtoolforin situ measurementofturfsurfacesandisoneofthefewmethodswithsolidsupportinthepublished literature.ifthepenetrometerdataacquisitionprocesswerebeautomatedtoeliminatetheoperator judgmentthatiscurrentlyrequired,andifthecollecteddatawerelinkedtogpscoordinates,the resultingdynamicpenetrometersystemwouldprovideaverypromisingtoolforcharacterizingturf racingsurfaces. InNorthAmerica,thetermpenetrometerisgenerallyusedtorefertoapointedprobethatis pressedintothesoilwhilethepenetrationforceismeasured.foragriculturalapplications,thisisan importantmeasurement,sincecropyieldisrelatedtothecompactionofthesoilintherootzone,and theprofileofthesoilcompactioncanbemeasured.dependingonthecroptobegrowninasoil,the allowablecompactionorpenetrationresistanceatadepthmaybewellcharacterized.becausethe speedofpenetrationisnotcontrolled,indampsoiltheoperatormusttakegreatcaretoensurethatthe speedoftheprobeissufficientlyslowthatthepropermeasurementofpenetrationwhichisrelevantfor rootsisobtained.liketheclegghammer,theagriculturalpenetrometerisausefultoolforitsintended purpose.inthecaseoftheagriculturalpenetrometer,thequasi staticpenetrationresistanceofsoil mayberelatedtothepenetrationresistanceofahoofonasurface,oritmaybeindependent. Certainly,atthehighspeedsatwhichahoofpenetratesthesurface,themoisturecontentandthusthe dynamicpropertiesareofcriticalimportance.liketheclegghammer,thepenetrometercanalsomake itpossibletodetermineifafalsebasetypesurfacehassetupsufficiently,orifatrackwhichusesapad hassetupexcessively.whilebothofthesemeasurementsmaybeusefulfordailymaintenancesupport forthetracksurfaceandforidentifyingintervalsatwhichthetrackshouldbehavedeepermaintenance, thesemeasurementtoolsarenotlikelytobewellsuitedforpredictingeithertheperformanceorthe risktothehorse. TheGoingStick:Atanintermediatelevelofcomplexityforin situcharacterizationofracingsurfacesis thegoingstick(turftraxltd,cambridgeshire,uk).thisdevicehastwoloadcellsandisusedmanually inacombinedtwoaxesofmotiontomeasuretheracingsurfaces.thesystemsarebestsuitedforuse ontheturf,whichisconsistentwiththeoriginsofthedeviceintheukwheremostracingisheldonturf. Likethedynamicpenetrometer,theGoingStickassumesthatthetrackconsistsofahomogenoustop 21

24 layer.unlikethedynamicpenetrometer,thegoingstickmeasurestheforcerequiredtopenetrateaflat bladeintothesurface.however,afterthebladeisplacedinthesurface,thetopofthegoingstickis thenrotatedaboutthebasesothatthehandleisata45 degreeangletothevertical.bymeasuringthe peakforceinatwoaxisloadcell,informationaboutnotonlythepenetrationresistancebuttheshear strengthofthesurfaceisobtained.fromabiomechanicalperspectivethismeasurementhassome characteristicsincommonwiththebreakoverandpropulsionphaseofthegait.whilethismaynotbe themostcriticalmeasurementwithrespecttoinjurytothehorse,thepropulsivephaseisvery importantfortheperformanceofthehorse.asaresultoftheoriginsofthisdeviceasatoolfor providingdataforthepublic,theinterpretationofthemeasurementphysicsofthegoingstickseems consistentwiththegoalsofthedevice.whileanarrowlyfocusedstudywaspublishedontheefficacyof someoftherelatedhardwarefordetermininghorseposition(spenceetal.2008),ingeneral,thegoing Stickisnotsupportedbyanydatathatispublishedintheopenliterature.Inspiteoftheabsenceofany scientificsupportfortheirapproach,ofalltherelativelysimpledevicesforcharacterizingasurface,the GoingStickisthedevicewiththegreatestpotential. However,severalcaveatsexistwiththeGoingStick.Whilethepenetratingprobeislargerthan thedynamicpenetrometer,itisstillmuchsmallerthanthefootofthehorse.assuch,anycomponent ofthetrackthatmaybeonthesamescaleastheprobecanbeaproblem.forexample,rootstructures inwarmweathergrassesandtherubberparticlesinsomesyntheticsurfacesareaslargeasthewidthof theprobe.furthermore,thedeviceisinsertedmanuallyintotheground.speedofinsertioniscritical sincesoilisstrainratedependentespeciallyatthehighermoisturecontentsseeninmanydamp surfaces.thismakestheoperatortechniqueverycriticaltotheproperuseofthistool.inthefuture, useofthistoolhasverygoodpotentialforusewithturfsurfaces,especiallyforcoolweathergrasses. Forsometypesofsyntheticsurfacesitmayalsobeuseful.Additionalworkisneededtounderstandthe useofthemeasurementandtosupportanyassociationwithrisktothehorse. BiomechanicalHoofTester:TheBiomechanicalHoofTesterisasystemthathasbeendevelopedmore recentlyprimarilyinresponsetothelimitationsoftheothertestingmethodsdescribedabove.withthe BiomechanicalHoofTester,itispossibletoloadthetrackattherateandloadsthatareappliedbya horseatagallop(petersonetal.2008).thissystemmimicsthepointatwhichtheforelimbcontacts thetrackandtheweightofthehorseistransferredtothehoof.thisistheperiodofthegaitduring whichboththehighestverticalloadsandthehighestshearloadsareappliedtothesoil(biewener, 2003).Thedevicethathasbeendevelopedisatwoaxisdroptowertypeofapparatuswhichimpactsa synthetichoofatanangletothesoilsurface(figure3).twonon orthogonalaxesofmotionallow accelerationduetotheslidingofthehoofincontacttobemeasured,aswellasverticalloadsand verticalacceleration. InFigure3,thetwoaxescanbeseenasalongsetofrailsandashorterlinearbearingapparatus thatisattachedtothehoof.withgravityactingonthefirstaxis(thelongrailsonwhichthehoofand instrumentationslides),theforceisgeneratedbyacceleratingthismassdowntherails.thetotalmass oftheportionofthesystemthatdropsonthelongrailsis30kg,whichprovidesenergyatimpactof approximately540j.thisimpactenergyaccountsfortheenergyofthehoofimpactingthesurfaceas wellasthepartialweightoftheanimalandassociatedmusculature.asecondsetofshorterlinearrails 22

25 movesdownasapartofthemassattachedtotheslide.thissecondaxisispreloadedbyagasspring andonlymovesoncethehoofisincontactwiththesoil.thedifferenceintheanglebetweenthefirst andsecondaxes(5degreesfromthelongrailangle)forcesthehooftoslideforwardtowardsthetoeas itimpactsthesoilandthesecondpreloadedaxisiscompressed.theangleatwhichthehoofimpacts thesoilisadjustedtomatchthepublishedbiomechanicaldataforinitialimpactofthehoof(ratzlaffet al.1993).atotaloffivedatachannelsata4khzsamplingratearerecordedduringthetesting. Attachedtoastiffmassabovethehoofisathree axis100gaccelerometer.loadistransferredintothe gasspringfromthehoofmassusingadynamicloadcellwitha0hz(dc)to36khzbandwidth. Redundantdatafromtheaccelerationandthepositionmeasurementisusedtoestimatethe penetrationintothesoilandtoverifythevelocityofthehoofatimpact.theangleofthehoofwith respecttothesoilisadjustedtosevendegreesfromtheverticaltomatchtreadmilldatafromhorsesat agallop. ThetwoparametersthathavebeenusedfromtheBiomechanicalHoofTesterarethepeakload andtheaccelerationsinthehorizontalandverticalplanes.however,theentiredatasetconsistingof loadsandaccelerationsonthehoofareacquiredwhichprovidesopportunitiestoconsiderother parametersthatmaybebettersuitedtocharacterizingtheperformanceofthesurface,includingimpact injuryscores(dallapetal.2010)andtotalenergyreturn(nigg1995),amongothermeasures.one particularlyimportantparameterthathasnotbeenconsideredistheeffectofthetuningofthetrackon theenergyreturn.aspreviouslymentionedinthediscussionoflaboratoryperformancetests,the potentialexistsbasedonexperiencewithhumanathletestoproduceasurfacethatcanbefastaswell assafe,throughthetuningofthenaturalfrequencyofthesurfacetothestridefrequencyoftheathlete (McMahonandGreene1979).SomedataiscurrentlyavailablefromtheBiomechanicalHoofTester; however,itremainstobeshownthatthedynamicresponseiscorrelatedwiththeresponseofthehorse atagallop. Althoughthemachineislargeandsomewhatcomplex,unliketheothertools,thebiomechanical hooftesterreplicatesthespeedandimpactofoneofthemostcriticalphasesofthegaitforrisktothe horse.whilethetwomeasuredcharacteristics,shearandimpactforce,areexpectedtoberelatedto performanceofthehorse,itisevenmorelikelythattheseparametersmeasuredwiththefullloadand speedofthehooflandingrepresenttherisktothehorseofcatastrophicinjurytotheforelimb.the biomechanicalhooftesterhasbeenshowntobecapableofmeasuringtheeffectoftypicalmaintenance onasurface(petersonandmcilwraith2008).asufficientlylargestudyhasnotyetbeendonethat makesitpossibletolinkthesemeasurementstorisktothehorse.theimmediateeffectofthe availabilityofthistoolistobeabletocharacterizethoseaspectsofthesurfacethatposethegreatest riskofcatastrophicandcareerendinginjury.evenintheabsenceofalargeepidemiologicalstudy, methodsthatarelikelytoresultinmoreconsistentsurfaceswillmoveracingtowardthegoalof providingasafersurface.itisalsolikelythatdatawillbeavailablethatcanalsobeusedtopredict performanceofthehorseonasurface.thislessambitiousgoalcreatesapotentialforthetestingto provideinformationtothepublic,whichcanhelptosupporttheneedtodocontinuedtesting,whichin turnwillprovidethedatathateventuallycanbeusedtoestimatetherisktoahorse. 23

26 Figure3:Biomechanicalhooftesterusedtoreplicatethespeedandloadingbythehoofon theracingsurface. UNDERSTANDING RACING SURFACE SAFETY Beyondthetoolsneededformonitoringofracingsurfaces,thereisaneedtounderstandwhat isdonetothesurfaceandhowthesesurfacesareused.theconditionofaracingortrainingsurfaceisa resultofmaintenance,material,weatherandusage.acompleteunderstandingofthesurfacecanonly beobtainedifthesefactorsareallincludedtounderstandtheoutcomeintermsoftheresultingsurface performance.theperformancecanthenbemeasuredrelativetotheseinputs.inatleastthreecases thishasalreadybeendone:thespeedofasyntheticsurfacerelativetothematerialtemperature (Petersonetal.2008),theeffectofmoistureonperformance(Murphyetal.1996)andtheeffectof maintenanceonthemeasurementsmadewiththebiomechanicalhooftester(petersonandmcilwraith 2008).Thesestudiesalsoshowthecorrelationofinputsonthesurfaceontheperformance,which makesitclearthatcontrolandmeasurementofinputshasthepotentialbothtocreateamore consistentsurfaceandtounderstandtheeffectonthematerialofvariousenvironmentalandother externalcharacteristics. Climate and Design Thefirstaspectofalarge scaleprojectistounderstandtheinteractionofclimateandtrack surfacedesign.whiletoacertainextentthedesignofatracksurfaceisaresponsetolocalmaterials andtradition,itisprimarilyaresponsetothelocalclimate.inaridregions,theretentionofmoisture andtheabilitytooperatewithadriertrackhavebeendominantinthedesignoftracks.conversely,in areaswithfrequentheavyrainfall,thepriorityisonaquickdrainingtrackthatcanretaintheintegrityof 24