Purpose:Thisstudywasdesignedtocharacterizeandcomparethevertical(kvert)andleg(kleg)stiffnessmeasuredduringrunningintwodifferentfootwearconditionsonnegative,level,andpositiveslopes,usingkinematicdataonly.Methods:Fourteenmalerecreationalrunners(age23.44.4years,height177.55.2cm,andbodymass69.55.3kg)weretestedon2separatedayswithin1week.Ateachsession,subjectsranseven5-mintrialsonatreadmillat10km/h,interspersedwith5minofsittingpassiverecovery.Eachtrialwasperformedonadifferentslopegradient,rangingfrom8%(downhill)tot8%(uphill),assignedinarandomorder.Furthermore,eachsubjectranone5-mintrialwearingminimalshoes(MS)andthesubsequenttrialwearingtraditionalshoes(TS)inacounterbalancedrandomizedorderensuringthateachslopewasranonceinMSandonceinTS.Kinematicdatawerecollectedusingaphotocellmeasuringsystemandhigh-speedvideocamera,withkvertandklegstiffnessbeingcalculatedfromthesedata.Results:Legcompression,contacttimes,andverticaldisplacementofthecenterofmassduringrunningweresignificantlysmallerinMScomparedtoTSacrossallslopes.Inthetwofootwearconditions,stepfrequencysignificantlyincreasedwitha(positive)increaseinslope.KinematicanalysesindicatedthatklegwasgreaterwhenrunninginMSthanTSandthisbetween-footweardifferenceremainedsimilaracrossslopes.Onthecontrary,kvertdidnotchangeonthebasisoffootwear,butincreasedwithpositiveincreasesinslope.Conclusion:Thisstudyshowedthatkvertandklegduringrunningresponddifferentlytochangeinfootwearand/orslope.Thesetwostiffnessmeasurescanhenceprovideauniqueinsightonthebiomechanicaladaptationsofrunningundervaryingconditionsandtheirrespectivequantificationmayassistinfurtheringourunderstandingoftraining,performance,and/orinjuryinthissport.
