Background:Manydisease-specificfactorssuchasmuscularweakness,increasedmusclestiffness,varyingposturalstrategies,andchangesinposturalreflexeshavebeenshowntoleadtoposturalinstabilityandfallriskinpeoplewithParkinson'sdisease(PD).Recently,analyticaltechniques,inspiredbythedynamicalsystemsperspectiveonmovementcontrolandcoordination,havebeenusedtoexaminethemechanismsunderlyingthedynamicsofposturaldeclinesandtheemergenceofposturalinstabilitiesinpeoplewithPD.Methods:Awavelet-basedtechniquewasusedtoidentifylimitcycleoscillations(LCOs)intheanterior–posterior(AP)posturalswayofpeoplewithmildPD(n=10)comparedtoage-matchedcontrols(n=10).Participantsstoodonafoamandonarigidsurfacewhilecompletingadualtask(speaking).Results:Therewasnosignificantdifferenceintherootmeansquareofcenterofpressurebetweengroups.Threeoutof10participantswithPDdemonstratedLCOsonthefoamsurface,whilenoneinthecontrolgroupdemonstratedLCOs.AninvertedpendulummodelofbipedalstancewasusedtodemonstratethatLCOsoccurduetodisease-specificchangesassociatedwithPD:time-delayandneuromuscularfeedbackgain.Conclusion:Overall,theLCOanalysisandmathematicalmodelappeartocapturethesubtleposturalinstabilitiesassociatedwithmildPD.Inaddition,thesefindingsprovideinsightsintothemechanismsthatleadtotheemergenceofunstablepostureinpatientswithPD.
