jsr - ward - coaching appl. - 46 volume 26... · j. swimming research, vol. 26.1 (2018) 25 during...

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CoachingApplicationsKinematicAnalysisofPeakVelocitiesintheBreaststrokeasaFunctionoftheTimingoftheKickSusanM.Ward1,JanPrins1,andBretG.Freemyer11DepartmentofKinesiologyandRehabilitationScienceAquaticResearchLaboratoryTheUniversityofHawai'iatMānoa 2500CampusRoadHonolulu,HI96822ABSTRACTThepurposeofthisstudywastodeterminetheeffectsofthetimingoftheBreaststrokekickonintra-cyclicvelocityfluctuations.ResearchersexaminedpeakhipvelocitiesofBreaststrokeswimmerstodetermineanysignificantvelocitydrop-offsandmagnitudeofvelocityregainedbetweendifferentkickingtechniques.Subjectsperformedswimmingtrialswiththreedifferentkickprotocols:aconventionalkick,alatekick,andadelayedlatekick.VideoanalysiswasusedtoanalyzepeakandminimumhipvelocitieswithinoneBreaststrokecycleforeachtrial.DatawasanalyzedusingANOVArepeatedmeasuresanalysis.Majorfindingsofthisstudywerethatduetosmallerpercentagesofhipvelocitydrop-off,greaterswimmingefficiencymaybeachievedwhenthekickisinitiatedduringtheinsweeporearlyrecoveryarmphasesandthatvideoanalysisandverbalcueingareviabletoolstohelpswimmersimprovetheirregularstroketechnique.

Introduction

TheBreaststrokecanbebrokendownintothreephases,theKick,thePull,andtheGlide.Whenthesethreephasesarecompletedinsuccession,aswimmerhascompletedonefullcycleoftheBreaststroke.ThevariationsintheoverallswimmingvelocitythroughoutoneBreaststrokecycleareagoodindicatoroftheswimmer’sstrokeefficiency;themoreefficientaswimmer’sstrokeis,thebettertheywillperform(17).AnumberofcurrentstudieshaveexaminedthecoordinationofthearmsandthelegsduringtheBreaststrokecycle(4,8,19).Theearlierstudiesmainlyfocusonperiodsofpropulsionprovidedbyeachphaseandhowtheyaffecttheaccelerationanddecelerationoftheentirecycle.ThemostrecentstudybyvanHouwelingenetal.notedswimmersarecapableofmanipulatingtheirarm-legcoordinationresultinginintra-cyclicvelocityvariations.However,theirresultswereinconclusive.

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Duringthe2016Olympics,BritishswimmerAdamPeatywonthemen’s100-meterBreaststrokeraceinworld-recordfashionusingakicktechniquethatperformsthekickphaseoftheBreaststrokelaterthanitisconventionallytaught.Toourknowledge,thereiscurrentlynoresearchthatexamineshowthetimingoftheinitiationofthekick,whenoccurringduringdifferentphasesofarmpullcanaffectthepropulsion,acceleration,andconsequentlyintra-cyclicvelocityoftheBreaststroke.ThelackofresearchregardinganalysisofthetimingoftheBreaststrokekickislikelyduetherelativelynewnatureofthistechnique.However,giventhesurprisingeffectthistechniquehashadonAdamPeaty’sgold-medal,world-recordperformanceatthe2016Olympicgames,itisclearthatthistechniqueshouldbeinvestigatedtodetermineifhisperformancesweretheresultoftraining,orimprovedtechnique.Kinematicanalysisprovidesinvaluableinformationforbothswimmersandcoaches;videoplaybackallowsthemtoimmediatelyreviewaswimmer’stechniqueandobtainfeedbackformakingcorrections,anddigitalanalysisallowsaswimmer’sstrokeefficiencytobeformallyevaluatedandimproved(3-5,7,16).Thehiphasbeenvalidatedasthemostreliableanatomicallandmarktouseformeasuringintra-cyclicvelocityanditschangeswithinastroke;theframe-by-frameanalysisthatcanbeutilizedinaccompanimentwiththerecordedintra-cyclicvelocityfluctuationsallowsresearcherstopinpointwhichaspectsofthetechniquearecontributingtothefluctuationsinordertomakeimprovements(3-5,7,16,19).CurrentlytherearenopublishedstudiesthatexaminetheeffectsofthetimingoftheBreaststrokekickduringspecificpullphasesonintra-cyclicvelocityfluctuations.Theexpectationisthatthisresearchcanleadtoimprovedstrokeefficiencyandconsequentlyfasterswimmingtimes.ThepurposeofthestudyistodeterminetheeffectsofthetimingoftheBreaststrokekickonintra-cyclicvelocityfluctuations.Theexpectationisthatthroughthisinvestigationitcanbedeterminedifthetimingassociatedwitha“latekick”canprovidehigheroverallswimmingspeedsthanthe“conventionalkick”technique.

Methods

ParticipantsSubjectswererecruitedfromanNCAADivisionIswimmingteam(4males&5females).AllparticipantsswamBreaststrokeasoneoftheirprimarycompetitiveeventsandwerecurrentmembersofanNCAADivisionIswimmingteam.DesignThisstudyexaminedtheeffectsonpeakvelocityduringtheBreaststrokebyhavingtheparticipantsswimthreedifferenttrialsofexecutingthekickduringdifferentarmphasesofthestroke.Thepercentageofvelocitydrop-offandpercentageof

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velocityregained(peronestrokecycle)werethevariablesusedtoassessstrokeefficiencyforeachtrial.MeasuresThreehigh-speeddigitalcameras(BaumerModelHXGwithCMOSsensors),installedincustomhousings(TheSextonCompany,Salem,Oregon)wereusedforfilmingswimtrials.All3housingswereattachedtocustom-designedmountingframesandpositionedsoastoprovidethethreerequiredfieldsofview(Figure1).

Figure1.Synchronizedframesofthethreecameraanglesusedtofilmswimmingtrials.Thesubjectperformedatotalofthreetrialsof3specifiedswimmingprotocols.Thethreeprotocolsconsistedofthefollowing:

ProtocolOne(ConventionalStroke):Thesubject,whileswimmingtheBreaststroke,wasrequiredtousetheirregulartechnique,ataneffortthatcorrespondedtothepacetheywouldcompletea100-yardracesprint.Inallexceptasinglecase,thesubject’s“conventionalstroke”consistedoftheinitiationofthekickcoincidingwiththebeginningstageoftheinsweep,calledthe“earlyinsweep.”ProtocolTwo(LateKick):Thesubject,whileswimmingtheBreaststroke,wasrequiredtotimetheinitialdraw-upofthekicktocoincidewiththeperiodduringwhichthehandswereinthefinalstageofthesecondphaseoftheBreaststrokepullpattern(theinsweep),calledthe“lateinsweep.”ProtocolThree(DelayedLateKick):Thesubject,whileswimmingtheBreaststroke,wasrequiredtotimetheinitialdraw-upofthekicktocoincidewiththeperiodduringwhichthehandswerebeginningthe“recovery”phase,i.e.handsmovingforwards.Thevideodatawasthenuploadedtothedigitizingsoftware,whereitwasdigitizedandthefootagewassynchronizedtoproducedynamicpeakvelocity-timegraphstoanalyzethefluctuationsinpeakvelocities.Thetrialswerecomparedtoeachothertorecordtheresultingdifferencesbetweenthepeakvelocity,theminimumvelocityrecordedduringtheeffort,andthevelocityregainedasthenextstrokewasinitiated.

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Each subject’s stroke was digitized and analyzed using the Motus and Templosoftware. The percentage drop-off in peak velocity, percentage of the velocityregained,maximumhipvelocitygeneratedbythearms,andmaximumhipvelocitygeneratedbythelegswereseenthroughtheuseoftime-velocitygraphs(Figure2).

.Figure2.Velocity-TimegraphusedtoanalyzevelocitiesoftheBreaststrokeMaximumkneeflexionangleandtimetocompletekickweremeasuredbyusingTemplo’sanglemeasurefunctiononatime-stampedvideo(Figure3).

Figure3.Maximalkneeflexionangle. ResultsandDiscussion

ThepurposeofthisstudywastodescribethekinematicsoftheconventionalversusthelateBreaststrokekicktechniqueusingselectedvariablestodetermine

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theefficiencyofeachtechnique.Currently,onlyonestudyexiststhatexaminestheeffectsofthetimingoftheBreaststrokekickonintra-cyclicvelocity.However,thissinglestudybyvanHouwelingenetal.usedsubjectsthatwereof“average”competitiveexperience,andconsequentlynotclassifiedascompetingattheelitelevels.Theirconclusionswerelimitedtostatingthat“average-levelswimmersarecapableofadjustingtheirleg-armcoordinationwithacousticcueingandthatdifferenttimingofthekickdoesaffectintra-cyclicvelocityvariation”(19).Unfortunately,thisstudydoesnotspecificallyaddressleg-armcoordination,howtoreplicatethestudy,norweretheyabletoexplainhowthesefindingscouldbeappliedbycoacheswhentrainingswimmers.Consequently,ourstudyisthefirsttohavedefinedparameterstoclassifyleg-armcoordinationandincorporatethemintoaspecificvariationoftheBreaststrokeswimmingtechnique.Inordertobedesignatedasa“ConventionalStroke”,“LateKick”ora“DelayedLateKick”,thetimeatwhichthekickreached160degreesofflexionwasmatchedwiththephaseatwhichthepullingactionofthehandscoincidedwiththispositionoftheknee.Duringtheprotocolwherethesubjectswererequiredtoswimusingtheir“ConventionalStroke”,thedistinguishingfeaturewasthattheinitiationofkneeflexiontookplaceduringtheearlystagesofthesecondphaseoftheBreaststrokearmpull.Thisphaseistermedthe“earlyinsweep”whichisthelaterstageandconcludingportionofthepropulsivephaseoftheBreaststrokepull(Figures4aand4b).

Figure4a.Protocol1:Closeupofhandpositionduringtheearlyinsweep.

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Figure4b.Protocol1:Coincidentkneekick.

The“LateKick”wasthetimethehandswerecompletingthe“lateinsweep”(Figures5aand5b)and“DelayedLateKick”coincidingwiththepositionofthehandswhentheywerestartingtobethrustforwardsintotherecoveryphase(Figures6aand6b).

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Figure5a.Protocol2:Closeupofhandpositionduringthelateinsweep.

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Figure5b.Protocol2:Coincidentkneekick.

Figure6a.Protocol3:Closeupofhandpositionduringtheearlyrecovery.

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Figure6b.Protocol3:Coincidentkneekick.

Allninesubjectsofthisstudywereelite-levelswimmerswhowereallabletoperformeachspecifiedkicktechniquewithonlyverbalcueing.Theanalysisofeachsubject’strialsrevealedthatthesmallestpercentagesofvelocitydrop-offwereseenduringthe“delayedlatekick”technique.Thatis,whenthethreeprotocolswerecompared,thethirdprotocol,whenthesubjectswaiteduntiltheirhandsstartedtobeextendedforwards,weobservedthesmallestdrop-offinoverallhipvelocities.Thesecondphaseof“leastdrop-off”wastheprotocoldesignated“LateKick”,whenthehandswereapproachingthebody,duringthe“insweep”phaseofthearmpull.Thegreatestamountofvelocityregainedwasinthelatekicktechniqueandthedelayedlatekicktechnique.Thisindicatesasmallervelocityvariationwithinonestrokecycle,whichindicatesamoreefficientBreaststroketechniquethanthesubject’snormaltechnique.Thesefindingsareinagreementwiththeconclusionsreachedbytwoearlierpublishedmanuscripts(4,19).Therewerenosignificantdifferencesinpeakhipvelocitygeneratedbythearmsorpeakhipvelocitygeneratedbythelegsbetweenthesubjectswhenusingeitherofthethreeprotocols.However,thefastestoverallswimmingvelocitieswereachievedinthesubjects’regularBreaststroketechniquetrialsbeforetheywereaskedtomakeadjustmentstotheirstrokes.Theseresultswereexpectedbecauseallsubjectstestedwerecurrentlyin,orrecentlyconcluded,intensetraining,andwereinstinctivelyswimmingattheircurrenttrainingvelocities.

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Whatwasobservedwasthatthesubjectstendedtoincreasethedegreeofkneeflexion,thelatertheywereaskedtokickintheirstroke.Inregardstotheresearchquestionsposedforthisexperiment,itcanbeconcludedthattheinitiationofkneeflexiontoperformthekickduringdifferentphasesoftheBreaststrokepulldoesyieldsignificantdifferencesinhipvelocities.Whenthekickisinitiatedduringlaterphasesofthepull,thereislessofadrop-offinhipvelocitiesandhighervaluesforregaininghipvelocities–simplyput,theswimmersloselessvelocity,andarebetterabletoregainvelocitylost(increasingtheiroverallefficiency)whentheydelaytheinitiationofthekick.PracticalApplications

TheconclusionsderivedfromthisstudyareinagreementwiththecurrenttrendincompetitivesprintBreaststroketechnique.Althoughthetimingofthelegdraw-upduringthelongestcompetitivedistance,the200meters,stillshowsrelativelyearlydraw-upofthekick,thefindingsofthisstudyshowscleardifferenceswhenthereisadelaybeforetheinitiationofthekickwhenswimmingtheshortercompetitivedistances.Thisstudyrevealedthatbyvirtueofsmallerdecreasesintheperiodsofvelocity“drop-off”,higherswimmingvelocitiesmaybeachievedwhenthekickisinitiatedduringtheinsweeporearlyrecoveryarmphases.Thisstudyalsoprovesthatvideoanalysisandverbalcueingarebothviablefeedbacktoolsthatcanbeusedtohelpswimmerslearntomakeadjustmentstotheirregulartechniquestobecomemoreefficientinthewater.