Thehumanfootisaverycomplexstructurecomprisingnumerousbones,muscles,ligamentsandsynovialjoints.Astheonlycomponentincontactwiththeground,thefootcomplexdeliversavarietyofbiomechanicalfunctionsduringhumanlocomotion,e.g.bodysupportandpropulsion,stabilitymaintenanceandimpactabsorption.Theseneedthehumanfoottoberigidanddampedtotransmitgroundreactionforcestotheupperbodyandmaintainbodystability,andalsotobecompliantandresilienttomoderateriskyimpactsandsaveenergy.Howdoesthehumanfootachievetheseapparentconflictingfunctions?Inthisstudy,weproposeaphase-dependenthypothesisfortheoveralllocomotorfunctionsofthehumanfootcomplexbasedonin-vivomeasurementsofhumannaturalgaitandsimulationresultsofamathematicalfootmodel.Wepropsethatfootfunctionsarehighlydependentongaitphase,whichisamajorcharacteristicsofhumanlocomotion.Inearlystancejustafterheelstrike,thefootmainlyworksasashockabsorberbymoderatinghighimpactsusingtheviscouselasticheelpadinbothverticalandhorizontaldirections.Inmid-stancephase(~80%ofstancephase),thefootcomplexcanbeconsideredasaspringyrocker,reservingexternalmechanicalworkusingthefootarchwhilstmovinggroundcontactpointforwardalongacurvedpathtomaintainbodystability.Inlatestanceafterheeloff,thefootcomplexmainlyservesasaforcemodulatorlikeagearbox,modulatingeffectivemechanicaladvantagesofankleplantiflexormusclesusingmetatarsal-phalangealjoints.Asoundunderstandingofhowpersefunctionsareimplementedinasimplefootsegmentduringhumanlocomotionmightbeusefultogaininsightintotheoverallfootlocomotorfunctionsandhencetofacilitateclinicaldiagnosis,rehabilitationproductdesignandhumanoidrobotdevelopment.
