kinematic analysis of peak velocities in the breaststroke ... volume 26... · statistical analysis...

J.SwimmingResearch,Vol.26.1(2018)

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

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

Duringthe2016Olympics,BritishswimmerAdamPeatywonthemen’s100-meterBreaststrokeraceinworld-recordfashionusingakicktechniquethatperformsthekickphaseoftheBreaststrokelaterthanitisconventionallytaught.Toourknowledge,thereiscurrentlynoresearchthatexamineshowthetimingofthe


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initiationofthekick,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.

MethodsParticipants

SubjectswererecruitedfromanNCAADivisionIswimmingteam(4males&5females).Inclusionarycriteria:Breaststrokemustbeoneoftheirprimarycompetitiveevents;theymusthavereachedNCAADivisionIlevelsofcompetitiveexperience.Exclusionarycriteria:Non-experiencedcompetitiveswimmers;injurythatpreventsswimmerfromswimmingwithnormaltechnique;Breaststrokeisnotaprimaryraceeventfortheswimmer.Design

Thisstudyutilizedasingle-subjectdesignbyexaminingtheeffectsonpeakvelocity during the Breaststroke with three different trials of executing the kickduringdifferentphasesof thestroke. The independentvariablewasthetimingofthe kick (conventional, late, or delayed late) and the dependent variables were


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maximalknee flexionangle,peakarmvelocity,peak legvelocity, timetocompletekick,percentageofvelocitydrop-off,andpercentageofvelocityregained.Measures

Threehigh-speeddigitalcameras(BaumerModelHXGwithCMOSsensors),installedincustomhousings(TheSextonCompany,Salem,Oregon)wereusedforfilmingswimtrials.All3housingswereattachedtocustom-designedmountingframesandpositionedsoastoprovidethethreerequiredfieldsofview(Figure1).

Figure1.Synchronizedframesofthethreecameraanglesusedtofilmswimmingtrials.

Camera1wasusedforrecordingthefrontal,orhead-onview,ofthesubject’sprogressandwasmountedonaverticallyorientedframe.Thecamerawaspositionedatadepthof0.48meters(1.57feet).Camera2wasmountedonahorizontalplatformthatrestedonthebottomofthepoolatadepthof2.13meters(7feet).Thecamerawasalignedvertically,i.e.pointingupwardstothesurfaceandprovidedatransverseviewofthesubject’sprogress.Camera3wasmountedonalaterallypositionedframethatwasboltedtotheconcretedeckofthepool.Thecamerawaspositionedatadepthof0.48meters(1.57feet),similartothedepthofCamera1.ThelateralorientationofCamera3providedthedatafortheprogressofthesubjectinthelongitudinalplaneofmotion.Thedistancethesubjectwasrequiredtocoverineachtrialvariedbetween11.89and13.71meters(39to45feet).Thisdistancewasdeterminedbyplacingthecamerathatwasusedforrecordingthefrontal,orhead-onviewofthesubjectatadistanceof13.71meters(45feet)yardsfromthesideofthepoolfromwhichthesubjectwasrequiredtopush-offatthestartofeachtrial.Subjectswereinstructedtoswimdirectlytowardsthiscamera,approachingitascloseaspossiblewithoutcollidingwiththecamera.Thecameraswerecontrolledviadual9.14meter-long(30feet)Gigabit(GigE)Ethernetcablesconnectedtoadesktopcomputerlocatedonthepooldeck.Eachcamerahadtwocables-onecablewasassignedtocameracontrolandanothercablewasusedforframesynchronization.UnlikethelimitationsrelatingtomaximumfunctionallengthsinherentwhenusingFirewirecabling,GigEcablingdoesnothavealengthrestriction,whichallowedforoptimumplacementoftheunderwatercamerasinthepool.Rotationaljointsegmentswereidentifiedusingacustom-designedstringoflightemittingdiodes(LED’s),housedinwaterproofhousings.TheLED’swereducttaped


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tothebodyandpoweredbyabatterypackattachedtoabeltwornbythesubjectatthewaist.Templo(Contemplas,Kempten,Germany)motioncapturesoftwarewasusedforcapturingandrecordingthevideodata.Asecondsoftwarepackage,Motus,(Contemplas,Kempten,Germany),wasusedfordigitizing,dataanalysis,andgenerating“reports”.Thissoftwareincludeda“Multi2-D”(M2-D)feature,whichenabledmultiplecamerastobesynchronized.Eachsequencewasdigitizedusingacombinationofauto-trackingandmanualmodes.IBMStatisticalPackagefortheSocialSciences(SPSS)version23wasusedtorunstatisticalanalysis.AfterobtainingapprovalforthestudyfromtheUniversityofHawai‘iatMānoaUniversityInstitutionalReviewBoardfortheStudyofHumanSubjects,BreaststrokesubjectswererecruitedfromtheUniversityofHawai‘iatMānoaIntercollegiateSwimmingTeam.Subjectsreportedtothepoolatascheduledtime,andsignedaconsentform.Priortovideotaping,eachsubjectwasshownapreviouslydigitizedswimtrialsoastofamiliarizethemwiththeoutcomeofthevideotapingandresulting“report.”Followingtherecordingofeachsubject’santhropometricdata,theLEDlightsweretapedontospecificanatomiclandmarks(bilateralfingers,wrists,elbows,shouldersandrighthip).ThesubjectwasprovidedwithsufficienttimetoswimafewwarmuplapstogetaccustomedtoswimmingwiththetapedLEDlightstrings.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.Subjectswereaskedtorepeatatrialiftheydidnotmeetthecriteriaforagivencondition,withamaximumofthreetrialspercondition,andweregiventimetorestbetweentrialsinordertoeliminatefatigueasaconfoundingvariableduringthesecondandthirdtrials.


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Thevideodatawasthenuploadedtothedigitizingsoftware,whereitwasdigitizedandthefootagewassynchronizedtoproducedynamicpeakvelocity-timegraphstoanalyzethefluctuationsinpeakvelocities.Thetrialswerecomparedtoeachothertorecordtheresultingdifferencesbetweenthepeakvelocity,theminimumvelocityrecordedduringtheeffort,andthevelocityregainedasthenextstrokewasinitiated.StatisticalAnalysis

Eachsubject’sstrokewasdigitizedandanalyzedusingtheMotusandTemplosoftware. The percentage drop-off in peak velocity, percentage of the velocityregained,maximumhipvelocitygeneratedbythearms,andmaximumhipvelocitygeneratedbythelegswereseenthroughtheuseoftime-velocitygraphs(Figure2).

Figure2.Time-velocitygraphusedtoanalyzevelocitiesoftheBreaststroke.MaximumkneeflexionangleandtimetocompletekickweremeasuredbyusingTemplo’sanglemeasurefunctiononatime-stampedvideo(Figure3).Duetothesingle-subjectdesignofthisstudy,eachsubject’sowntrialswereanalyzedagainsteachothertonoteanysignificantdifferenceinthetimingoftheBreaststrokekickonpeakvelocity(notedifferenceindrop-off/regained);forexample,subject1’sProtocol1trial,Protocol2trial,andProtocol3trialwereallcomparedagainsteachother,butsubject1’sProtocol1trialwasnotcomparedagainstsubject2’sProtocol1trial.Foreachdependentvariable,allofthedatavarianceforeachsubjectwascomparedagainstrespectivedatavariancefortheothersubjectsforalltrials;forexample,subject1’smaximalkneeflexionangleforProtocol1trialwascomparedtosubject2’smaximalkneeflexionangleforProtocol1trial.ThesignificantdifferenceforeachprotocolwasdeterminedusingANOVArepeatedmeasuresanalysiswithasignificancelevelsettop=0.05(6).


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Figure3.MaximalkneeflexionanglecalculatedinTemplo.

Mauchly’stestofsphericitywasruntovalidatetheparametersoftheANOVArepeatedmeasuresanalysiswithasignificancelevelsetatp=0.05(6).Greenhouse-GeisserandHuynh-FeldtcorrectionswereusedwiththeMauchly’stest;Huynh-Feldtcorrectionwasusedforpeakhipvelocitygeneratedbythelegs,andGreenhouse-Geissercorrectionwasusedforallotherdependentvariables(6).ResultsSubjectsinthisstudyweren=9NCAADivisionIswimmers.Anthropometricdatacollectedforthesesubjectsincluded:age,height,weight,bodymassindex,andwingspan.Thedataisdisplayedintable1.Followingthestatisticalanalysisoftheirtrials,themeans,standarddeviations,and95%confidenceintervalsforallvariableswerecalculatedandarereportedintable2.Alsocalculatedintable2arepairwisecomparisonsofdatatodemonstratesignificancebetweenthethreedifferentkicktechniquesforeachdependentvariable

Table1.Anthropometricmeasurements

Variable Mean SDAge,years 20.67 1.32Height,in. 70.34 3.81Weight,lb. 158.34 16.96Bodymassindex,kg/m2 22.49 1.56Wingspan,in. 71.11 5.73SD=StandardDeviation


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. Table2.ComparisonofBreaststrokeBiomechanicswithDifferentKickTechniques.

Measure

C100 DU1 DU2

Mean±SD CIp-value

Mean±SD CIp-value

Mean±SD CIp-value

DU1 DU2 C100 DU2 C100 DU1%VDO 91.2±4.9 91.3±3.8 0.02 0.01 86.8±5.0 86.8±3.8 0.02 0.03 82.5±5.2 82.5±4.0 0.01 0.03%VR 91.1±11.8 91.1±9.1 0.02 0.01 96.3±11.6 96.4±9.0 0.02 0.39 97.3±10.2 97.3±7.9 0.01 0.39MKF,O 36.1±5.1 36.1±4.0 0.22 0.03 33.7±6.8 33.7±5.2 0.22 0.03 31.6±6.1 31.6±4.7 0.03 0.03PAV,m/s 2.2±0.5 2.2±0.4 0.10 0.06 1.9±0.3 2.0±0.3 0.10 0.23 1.9±0.4 1.9±0.4 0.06 0.23PLV,m/s 2.0±0.4 2.0±0.3 0.42 0.27 1.9±0.3 1.9±0.3 0.42 0.43 1.8±0.4 1.8±0.3 0.27 0.43TCK,s 0.6±0.1 0.7±0.1 0.02 0.05 0.7±0.1 0.7±0.1 0.02 0.36 0.7±0.1 0.7±0.1 0.05 0.36

%VDO=PercentageVelocityDrop-off;%VR=PercentageofVelocityRegained;MKF=MaximumKneeFlexionAngle;PAV=PeakHipVelocityGeneratedbytheArms;PLV=PeakHipVelocityGeneratedbytheLegs;TCK=TimetoCompleteKick;C100=ConventionalStroke100-ydsprintpace;DU1=LateKick;DU2=DelayedLateKick;SD=StandardDeviation;CI=ConfidenceInterval


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ComparativeSignificantDifferences

Whencomparing“ConventionalStroke”andthe“LateKick,”significantdifferenceswereseeninthefollowingparameters:

a) Timetakentocompletekick.b) Percentageofhipvelocitydrop-off.c) Percentageofvelocityregained.

Whencomparing“ConventionalStroke”andthe“DelayedLateKick,”significantdifferenceswereseeninthefollowingparameters:

a) Maximalkneeflexionangle.b) Timetakentocompletekick.c) Percentageofhipvelocitydrop-off.d) Percentageofvelocityregained.

Whencomparingthe“LateKick”tothe“DelayedLateKick,significantdifferenceswereseeninthefollowingparameters:

a) Maximalkneeflexionangle.b) Percentageofhipvelocitydrop-off.

ToensurethevalidityofthesignificancefoundintheANOVArepeatedmeasuresanalysis,Mauchly’stestofnon-sphericitywasrun.Huynh-Feldtcorrectionwasusedforpeakhipvelocitygeneratedbythelegs,andGreenhouse-Geissercorrectionwasusedforallotherdependentvariables.Partialetasquaredwasalsocalculatedtodeterminehowmuchofthechangeseenineachvariablecouldbeattributedtotheconditionalone.Changesinkickprotocolaccountfor11-56%ofthedifferenceseenforeachdependentvariable.Thisdataisshownintable3.

PeakhipvelocitygeneratedbythearmswastheonlyvariablefoundsignificantintheMauchly’stestofnon-sphericity(p=0.04);Greenhouse-Geissercorrectionwasusedtodeterminesignificanceforthisvariable(p=0.07).Therefore,allthesignificantvaluesfoundintheANOVArepeatedmeasuresanalysiscanbeconsideredvalid.DiscussionThepurposeofthisstudywastodescribethekinematicsoftheconventionalversusthelateBreaststrokekicktechniqueusingselectedvariablestodeterminetheefficiencyofeachtechnique.Currently,onlyonestudyexiststhatexaminestheeffectsofthetimingoftheBreaststrokekickonintra-cyclicvelocity.However,this

MeasureMauchly’s Greenhouse-Geisser Huynh-Feldt

Sig. W Sig. PartialEtaSq. Sig. PartialEtaSq.%VDO 0.05 0.435 0.01 0.558 0.01 0.558%VR 0.28 0.695 0.01 0.516 0.00 0.516MKF,O 0.08 0.489 0.05 0.354 0.05 0.354PAV,m/s 0.04 0.411 0.07 0.331 0.06 0.331PLV,m/s 0.11 0.531 0.36 0.110 0.36 0.116


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singlestudybyvanHouwelingenetal.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”ascomparedtothe“lateinsweep”whichisthelaterstageandconcludingportionofthepropulsivephaseoftheBreaststrokepull(Figures4aand4b).

Figure4a.Protocol1:Closeupofhandpositionduringtheearlyinsweep.


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Figure4b.Protocol1:Coincidentkneekick.

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

.

Figure5a.Protocol2:Closeupofhandpositionduringthelateinsweep.


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Figure6a.Protocol3:Closeupofhandpositionduringtheearlyrecovery.



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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.Maximalkneeflexionangleandtimetocompletekickaretwovariablesthathavenotyetbeenstudiedasitrelatesarm-legcoordinationoftheBreaststroketechniqueandintra-cyclicvelocityvariations.MaximalkneeflexionwassignificantlydifferentbetweentheregularBreaststroketechniqueandthedelayedlatekicktechnique,butnotbetweentheregularBreaststroketechniqueandthelatekicktechnique.Whatwasobservedwasthatthesubjectstendedtoincreasethedegreeofkneeflexion,thelatertheywereaskedtokickintheirstroke.Thesechangesmaybeattributedtotheperceptionoftheoverallstrokecycletakingmoretime,therebyallocatingmoretimetoincreasetheamountofkneeflexion.Asexpected,thisalsoincreasedthetotaldurationsofthe“LateKick”and“DelayedLateKick”whencomparedtothedurationsofthesubjects’kickwhenswimmingtheir“ConventionalStroke”.Inregardstotheresearchquestionsposedforthisexperiment,itcanbeconcludedthatthereisasignificantdifferencebetweenhipvelocitiesasafunctionoftheinitiationofkneeflexionandhandpositionsduringtheBreaststrokepullphase.Itcanbeconcludedthatthereislessofadrop-offinhipvelocities,andhighervaluesforregaininghipvelocities,accompanyinglaterdurationsofthepullphase.PracticalApplicationsTheconclusionsderivedfromthisstudyareinagreementwiththecurrenttrendincompetitivesprintBreaststroketechnique.Althoughthetimingofthelegdraw-upduringthelongestcompetitivedistance,the200meters,stillshowsrelativelyearlydraw-upofthekick,thefindingsofthisstudyshowscleardifferenceswhenthereis


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adelaybeforetheinitiationofthekickwhenswimmingtheshortercompetitivedistances.Thisstudyrevealedthatbyvirtueofsmallerdecreasesintheperiodsofvelocity“drop-off”,higherswimmingvelocitiesmaybeachievedwhenthekickisinitiatedduringtheinsweeporearlyrecoveryarmphases.Thisstudyalsoprovesthatvideoanalysisandverbalcueingarebothviablefeedbacktoolsthatcanbeusedtohelpswimmerslearntomakeadjustmentstotheirregulartechniquestobecomemoreefficientinthewater.References1. Barbosa,T.M.,Marinho,D.A.,Costa,M.r.J.,&Silva,A.n.J.(2011).Biomechanics

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