简介：Traditionalbiomechanicalanalysesofhumanmovementaregenerallyderivedfromlinearmathematics.Whilethesemethodscanbeusefulinmanysituations,theydonotdescribebehaviorsinhumansystemsthatarepredominatelynonlinear.Forthisreason,nonlinearanalysismethodsbasedonadynamicalsystemsapproachhavebecomemoreprevalentinrecentliterature.Theseanalysistechniqueshaveprovidednewinsightsintohowsystems(1)maintainpatternstability,(2)transitionintonewstates,and(3)aregovernedbyshort-andlong-term(fractal)correlationalprocessesatdifferentspatio-temporalscales.Thesedifferentaspectsofsystemdynamicsaretypicallyinvestigatedusingconceptsrelatedtovariability,stability,complexity,andadaptability.Thepurposeofthispaperistocompareandcontrastthesedifferentconceptsanddemonstratethat,althoughrelated,thesetermsrepresentfundamentallydifferentaspectsofsystemdynamics.Inparticular,wearguethatvariabilityshouldnotuniformlybeequatedwithstabilityorcomplexityofmovement.Inaddition,currentdynamicstabilitymeasuresbasedonnonlinearanalysismethods(suchasthefinitemaximalLyapunovexponent)canreveallocalinstabilitiesinmovementdynamics,butthedegreetowhichtheselocalinstabilitiesrelatetoglobalposturalandgaitstabilityandtheabilitytoresistexternalperturbationsremainstobeexplored.Finally,systematicstudiesareneededtorelateobservedreductionsincomplexitywithaginganddiseasetotheadaptivecapabilitiesofthemovementsystemandhowcomplexitychangesasafunctionofdifferenttaskconstraints.

简介：Purpose:Thepurposeofthisstudywastocompare4techniquesforarrivalatabaseaftersprintingmaximallytoreachit:slidinghead-first,slidingfeet-first,runningthroughthebasewithoutslowing,andstoppingonthebase.Asecondarypurposeofthestudywastodetermineanyadvantagetheremaybetodivingintofirstbasetoarrivesoonerthanrunningthroughthebase.Methods:Twohigh-definitionvideocameraswereusedtocapture3-dimensionalkinematicsofslidingtechniquesof9intercollegiatebaseballplayers.Anothervideocamerawasusedtotimerunsfromfirstbasetosecondin4counterbalancedconditions:runningthroughthebase,slidinghead-first,slidingfeet-first,andrunningtoastop.Mathematicalmodelingwasusedtosimulatedivingtofirstbasesuchthattheslidewouldbeginwhenthehandtouchesthebase.Results:Baseduponoverallresults,thequickestwaytothebaseisbyrunningthroughit,followedbyhead-first,feet-first,andrunningtoastop.Conclusion:Therewasanon-significanttrendtowardanadvantagefordivingintofirstbaseoverrunningthroughit,butmoreresearchisneeded,andeveniftheadvantageisreal,therisksofexecutingthistechniqueprobablyoutweightheminisculegain.