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What is the effect of compression garments on a balance task in female athletes?

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What is the effect of compression garments on a balance task in female athletes?
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  What   isthe   effect   of    compression   garments   on   a   balance   task   infemaleathletes?  JacobS.Michael a ,SeraN.Dogramaci a, *,   KylieA.Steel b ,KennethS.Graham a a  Applied   Research   Program,   New   South   Wales   Institute   of    Sport,   6    Figtree   Drive,   Sydney   Olympic    Park,   NSW     2127,    Australia b School   of    Science   and   Health,   University   of    Western   Sydney,   Penrith   Campus,   Locked   Bag    1797,   Penrith   South,   NSW    1797,    Australia 1.   Introduction Compression   based   garments   have   been   used   in   the   medical   fieldto   optimise   circulatory   dynamics   for   many   years   [1,2].   Compressiongarments   (CGs)   provide   a   means   of    creating   an   external   pressuregradient   at   the   surface   of    the   body   [2],that   demonstrates   improvedvenous   return   [3]   and   a   reduction   in   peripheral   swelling   [4].Although   a   significant   amount   of    research   exists   describing   thesepositive   roles   of    CGs   within   therapeutic   settings,   research   examiningsports-specific   useof    CGs   have   revealedmixed   results,   with   only   afew   reporting   performance   benefits.Research   data   related   to   exercise   and   wearing   CGs   hasdemonstrated   a   decrease   in   blood   lactate   concentrations   duringand   after   maximal   exercise   [5]   and   improvements   in   maximalaerobic   performance   in   repeated   5   min   maximal   cycle   efforts   [6].The   results   suggested   that   the   CGs   were   better   able   to   improverecovery   via   increasing   venous   return   and   aid   in   the   removal   of waste   products.   Moreover,   it   has   been   demonstrated   thatenhanced   repetitive    jump   performance   [7,8]   and   an   increasedvertical    jump   height   [9]   resulted   with   use   of    CGs.   In   addition   tothose   mentioned   above,   possible   mechanisms   may   includeenhanced    joint   proprioception   [7]   and   muscle   coordination   [10],as   well   as   assisting   muscle   contraction   via   the   reduction   in   muscleoscillation   during    jump   landings   [9].Contrary   to   these   reportshowever,   no   improvements   in   maximal   throwing   distance   [1],repeat   sprint   performance   [1,9]   or   prolonged   running/cyclingperformance   times   [3]   were   gained   whilst   wearing   CGs.Recently   Pearce   et   al.   [11]   found   visuomotor   tracking   perfor-mance   improved   while   participants   wore   CGs   during   and   afterrepetitive   eccentric   arm   exercise.   The   CG   is   thought   to   have Gait   &   Posture   39   (2014)   804–809 A   R    T   I   C   L    E   I   N   F   O  Articlehistory: Received   26   March   2013 Receivedinrevisedform24September2013 Accepted   4   November   2013 Keywords: ProprioceptionCompression   garmentMotor   learningFemaleAthlete A   B   S   T   R    A   C   T Objectives:   Toinvestigatetheeffectoflonglegcompressiongarmentsontheposturalswayandbalanceabilityoffemaleathletesatastatesportsinstitute. Design: Alaboratorywassetuptoanalysekineticandkinematicvariablesusingadoubleblind,randomisedcontrolledrepeatedmeasurescrossoverdesign. Method: Participantswererequiredtoperformasinglelegbalancetaskforupto60sacrosssixconditions;includingeyes-openandeyes-closedwhilewearingconventionalshorts(control),loose-fittedcompressiongarmentandwell-fittedcompressiongarments.Simultaneousmeasurementsof groundreactionforcesandfullbodyjointkinematicswererecorded.Posturalstabilitywasassessedbymeasuringtheoverallstabilisationtimeaswellasthemovementofthecentreofpressure(CoP)andcentreofmass(CoM)frombaselinemeasures. Results: Duringonelegstance,significantlygreaterposturalstability(  p < 0.01)wasobservedwitheyesopenvseyesclosed,irrespectiveofcompressiongroup.Asignificantlygreater(  p < 0.05)balancetimewasobservedwitheyesclosedwhenwearingwell-fittedcompressiongarmentscomparedtoconventionalshorts.Differenceswerenotpresentwithuseoftheloose-fittedgarment.Additionally,asignificantinteractioneffectbetweencompressionconditionandvisionwasobservedanalysingthevariationabout   thesway(swaySD)oftheCoPandCoMdata(  p < 0.05).Theinteractioneffectrevealedgreatervariabilityofmovementwitheyesclosedasparticipants’levelofcompressiondecreased.Nosignificantdifferenceswereobservedwitheyesopen. Conclusions: Thedifficultiesofposturalstabilitywhilemaintainingthesinglelegstancewearingconventionalshortswereimprovedwithuseofthewell-fittedcompressiongarments(intheeyes-closedcondition).Properfittedcompressiongarmentsmaybebeneficialforinjurymanagementandinjuryprevention.  2013ElsevierB.V.Allrightsreserved. * Corresponding   author.   Tel.:   +612   9763   0267. E-mail   address:   sera.dogramaci@nswis.com.au   (S.N.   Dogramaci). Contents   lists   available   at   ScienceDirect Gait&Posture jo   u   rn   al   h   omep   age:www.els   evier.co   m/loc   ate/g   aitp   ost 0966-6362/$   –   see   front   matter      2013   Elsevier   B.V.   All   rights   reserved.http://dx.doi.org/10.1016/j.gaitpost.2013.11.001  produced   increased   cutaneous   stimulation   allowing   for   improvedproprioceptive   feedback   and    joint   positional   awareness.   Further-more,   Cameron   et   al.   [12]   investigated   the   effect   of    CGs   on   a   legswing   task   in   Australian   Rules   football   players   and   found   highperforming   players   demonstrated   decreased   swing   discriminationscore   compared   to   less   skilled   players   who   improved.   In   contrast   tothe   results   found   by   Pearce   et   al.   [11]   the   increased   feedbackpresented   to   the   elite   players   via   the   cutaneous   sensory   receptorsin   the   skin,   may   have   presented   unfamiliar   feedback   that   wasdifficult   to   ignore   by   the   feedback   system.   Further,   less   skilledplayers   may   have   been   less   attuned   to   their   own   intrinsic   feedbackand   so   profited   from   the   novel   presentation   of    feedback   in   thiscase.   Despite   the   aforementioned   studies   there   is   a   paucity   of research   in   the   application   of    CGs   in   motor   control,   e.g.   balance.Balance   ability   in   sport   ranges   from   maintaining   an   uprightposture   to   executing   complex   sporting   skills,   and   is   required   tokeep   the   vertical   projection   of    the   centre   of    mass   over   the   base   of support   [13].   Constant   adjustments   and   counter-adjustments   of  joint   position   exist   (postural   sway)   which   maintain   equilibriumand   prevent   falling   [14].   Given   control   of    posture   is   maintained   bya   complex   interrelationship   between   sensory   informationobtained   from   the   somatosensory,   visual,   and   vestibular   systemsand   responses   of    the   musculoskeletal   system   regulating   bodyposture   and   movement   [15]   it   is   possible   that   these   systems   maybenefit   from   the   use   of    CGs.   Further,   research   has   shown   thatsuperior   balance   enhances   postural   control   [16]   athletic   perfor-mance   [17],and   is   associated   with   a   reduction   in   injury   rates   [18].Therefore   the   purpose   of    this   study   was   to   assess   the   effectivenessof    wearing   CGs   on   the   balance   ability   of    elite   athletes,   and   toinvestigate   the   effects   of    compression   garment   sizing   on   posturalcontrol.   We   hypothesised   that   greater   conscious   awareness   of    thebody’s   position   would   occur   as   a   result   of    wearing   CGs   during   a60   s   single-leg   balance   task. 2.   Methods Twelve   healthy   and   active   females   (24      7.2   yrs;   57.8      6.1   kg;168.3      6.3   cm)   volunteered   to   participate   in   this   study.   Participantswere   free   of    neurological   illness,   musculoskeletal   injury   or   anydisease/condition   that   would   interfere   with   their   normal   balance.University   Human   Ethics   Committee   (ref.   H8620)   was   provided   priorto   the   commencement   of    the   study   and   participants   gave   informedconsent   before   participating. Kinetic   and   kinematic   variables   were   measured   using   a   doubleblind,   randomised   controlled   repeated   measures   cross   over   designto   assess   the   effects   CGs   had   on   balance   during   single   leg   stance(SLS).   Participants   were   required   to   perform   three   balance   trials:wearing   conventional   shorts   (control);   loose   fitted   CGs   (LF-CG);and   well   fitted   CGs   (WF-CG),   on   two   occasions:   eyes   open   and   eyesclosed   (visual   occlusion).   The   CGs   were   fitted   to   participants   on   thebasis   of    the   company’s   guidelines   using   height   and   weight.   LF-CGwas   classified   as   loose-fitted   compared   to   the   normal   recom-mended   size.   Both   pairs   of    CGs   looked   identical   to   minimise   anyplacebo   effects.   Each   testing   session   began   with   the   conventionalshorts   condition   which   provided   baseline   measurements   forbalance   ability.   The   two   remaining   compression   garment   condi-tions   were   then   randomised   for   each   subject   to   minimise   anylearning   effect   that   may   occur   with   familiarity.   The   CGs   used   werestandard   commercial   sportswear   (itsports,   Sydney,   Australia)which   covered   the   area   from   the   waist   to   the   ankle   with   a   stirrupunder   the   foot.   All   participants   had   worn   compression   garmentsduring   their   sporting   careers;   however,   in   this   instance   the   athleteshad   not   worn   this   brand   of    garment.Prior   to   each   testing   condition,   instructions   were   givendirecting   the   participant   to   stand   in   a   comfortable   stance,balancing   on   their   dominant   leg   (stance   leg)   near   the   centre   of the   force   platform.   Participants   were   instructed   to   keep   their   non-weight   bearing   leg   (swing   leg)   in   approximately   15 8 of    flexion,   sothat   their   foot   was   level   with,   but   not   touching,   the   calf    of    theirstance   leg.   Additionally,   participants’   arms   were   kept   in   a   flexedposition,   with   their   hands   resting   on   their   hips.   Participants   wereallowed   to   move   their   arms   and   swing   leg   during   the   trial   as   astrategy   to   regain   balance   if    required,   but   were   instructed   to   returntheir   arms   and   swing   leg   to   the   initial   position   immediately   aftersway   was   controlled.   This   movement   was   allowed   to   representbalance   strategies   used   during   normal   balance   control.Each   trial   began   once   the   subject   was   in   a   ‘‘ready’’   position   andgave   a   verbal   cue   to   indicate   she   felt   comfortable   in   a   quiet,balanced   stance.   Similar   to   previous   studies   measuring   healthyand   active   participants   [19]   the   participants   in   the   current   studywere   required   to   maintain   this   SLS   for   a   maximum   of    60   s.   If    thesubject   became   unbalanced   during   the   trial   and   touched   the   floorwith   the   swing   leg,   the   test   was   terminated   and   the   total   time   of the   test   was   recorded.An   eight   camera   motion   analysis   system   (Vicon   MX   13;   OxfordMetrics   Ltd.,   Oxford,   United   Kingdom)   and   one   force   plate   (Kistler9281CA,   Winterthur,   Switzerland)   were   used   to   sample   theparticipant’s   kinematic   and   kinetic   motion   data,   respectively.Subjects’   3D   trajectories   and   3D   reaction   forces   were   capturedusing   a   motion   capture,   measurement   and   analysis   software(Vicon   Motion   Systems,   Nexus   v1.6,   Oxford,   United   Kingdom)using   the   plug-in   gait   full   body   model.   Raw   marker   trajectorieswere   filtered   using   Vicon’s   Woltring   quintic   spline   algorithm   witha   MSE   value   of    20.The   motion   analysis   software   enabled   synchronised   recordingof    the   three   dimensional   motion   data   with   the   analogue   forcechannel   simultaneously   recorded   during   each   balance   trial(sampled   at   250   and   500   Hz   respectively).   Thirty-five   sphericalshaped   retro-reflective   markers   were   used   to   define   15   rigid,linked   segments   of    the   participant   (head,   trunk,   upper   arms,forearms,   hand,   pelvis,   thighs,   shanks   and   feet)   during   each   trial(Fig.   1).The   3D   trajectories   of    the   reflective   markers   (14   mmdiameter)   were   computed   with   a   dynamic   accuracy   of    0.5   mm   [20].Centre   of    mass   (CoM)   was   determined   from   the   anthropometricand   kinematic   analysis   of    all   body   segments.   The   position   theparticipant   applied   weight   onto   the   force   platform   was   calculatedas   the   centre   of    pressure   (CoP)   which   was   computed   using   thedigitised   output   signals   of    the   force   platform   amplifiers. Fig.   1.   An   example   of    the   anatomical   landmark   locations   used   in   the   biomechanicalanalysis   of    the   participants   in   this   study.  J.S.   Michael   et    al.    /    Gait    &    Posture    39   (2014)   804–809   805  Each   balance   trial   was   analysed   for   all   participants.   The   mainoutcome   measures   for   this   study   included   the   overall   stabilisationtime   and   measurements   of    CoM/CoP   path   lengths.   Path   lengthmeasurements   include   CoM   and   CoP   range   differences   within   thesagittal   plane   (antero-posterior   axis)   and   the   frontal   plane   (medio-lateral   axis);   average   sway   within   the   CoM   and   CoP   time   series   andstandard   deviations   of    this   range   of    movement.   All   computationswere   based   on   the   total   stabilisation   time   acquired.The   antero-posterior   (AP)   and   medio-lateral   (ML)   coordinatesthat   define   the   CoM   and   CoP   path   were   computed   using   thedigitised   output   signals   of    the   force   platform   amplifiers.   Theparticipant   was   positioned   on   the   force   platform   facing   the   positiveAP   direction.   Thus   the   location   and   movements   of    the   CoM   and   CoPin   the   AP   and   ML    axis   during   SLS   were   recorded.   The   range   referredto   the   maximum   movement   of    the   CoM   and   CoP,   in   both   the   AP   andML    directions.   Range   was   calculated   as   the   maximum   distancebetween   any   two   points   on   the   time   series   path.   The   CoP   range   inthe   AP   direction   for   example,   was   the   absolute   value   of    thedifference   between   the   smallest   and   largest   values   in   the   AP   timeseries   for   CoP   data.   Similarly,   ML    range   was   calculated.   The   abilityto   keep   the   CoM   above   the   CoP   is   reflected   in   the   absolutedifference   between   the   two   variables   in   both   the   AP   and   ML directions   (the   CoM–CoP   range   difference).   This   measurement   of path   lengths   has   been   used   in   previous   research   [21]   and   shown   tobe   a   valid   and   reliable   measure   of    standing   balance   [21–23].Furthermore,   postural   sway   was   also   calculated,   and   defined   asthe   average   displacement   spent   away   from   the   central   point   of srcin   in   both   the   CoM   and   CoP   coordinate   time   series.   The   srcin   of the   CoM   and   CoP   path   was    X  – Y  coordinate   recorded   at   thebeginning   of    each   trial.   The   resultant   distance   was   calculated   as   thevector   distance   from   the   CoM   and   CoP   srcin   to   each   consecutivepoint   on   the   CoM   and   CoP   path   respectively.   Average   posturalsway,   the   mean   of    the   resultant   distance   time   series,   was   recorded,along   with   the   variability   (standard   deviations)   of    the   posturalsway   in   the   CoM   and   CoP   time   series.   The   swaySD   has   beensuccessfully   used   as   an   indicator   of    postural   sway   by   previousresearchers   [24].All   statistical   procedures   were   conducted   with   SYSTAT   (SYSTAT,Inc.,   Evanston,   IL).   A   two-way   analysis   of    variance   (compressioncondition      vision)   with   repeated   measures   was   used   to   test   thesignificance   of    any   observed   differences   in   the   means   of    theprimary   variables   and   to   determine   any   interaction   effects.   Aprobability   level   of     p   <   0.05   was   accepted   to   indicate   a   statisticallysignificant   difference   in   the   individual   comparisons.   Wheresignificance   was   reached,   a   Student–Newman–Keuls   post   hocanalysis   was   used   to   isolate   differences   among   conditions   [10].Alldata   are   presented   as   mean      standard   deviation   (SD). 3.   Results The   results   for   the   overall   stabilisation   time   are   presented   inFig.   2.A   significant   main   effect   was   observed   when   analysing   theeffect   of    vision   ( F  [1,11]   =   21.40,    p   <   0.05)   and   compressioncondition   ( F  [2,22]   =   5.34,    p   <   0.05).   A   significant   interaction   effectwas   also   observed   between   compression   condition   and   vision   fortotal   stabilisation   time   ( F  [2,22]   =   4.94,    p   <   0.05).   Post   hoc   testsrevealed   that   with   eyes   closed,   total   balance   time   wearing   WF-GGwas   significantly   greater   than   wearing   shorts   (Fig.   2).   Nosignificant   differences   among   the   three   compression   conditionswere   observed   in   the   eyes   open   condition,   with   all   subjectsmaintaining   the   60   s   stance   balanced   on   one   leg.Representative   graphs   for   the   maximum   displacement   of    theCoM   and   CoP   within   the   AP   and   ML    directions   are   presented   inFig.   3.Analysis   of    the   CoM   and   CoP   range   allowed   for   the   CoM–CoPrange   differences.   No   significant   main   effects   were   observedbetween   compression   conditions   when   analysing   the   CoM   and   CoPrange   in   the   AP   direction   ( F  [2,22]   =   1.58,    p   =   0.23   and F  [2,22]   =   0.75,    p   =   0.48   respectively)   or   ML    direction( F  [2,22]   =   3.40,    p   =   0.05,   and   F  [2,22]   =   1.93,    p   =   0.17   respectively).Furthermore,   no   significant   main   effect   was   found   analysing   theCoM–CoP   range   differences   in   the   AP   ( F  [2,22]   =   0.72,    p   =   0.50)   andML    directions   ( F  [2,22]   =   2.57,    p   =   0.10).   Post   hoc   tests   showed   thatwith   vision   and   compression   conditions   grouped,   a   significantlygreater   CoP   displacement   was   found   in   the   AP   direction   comparedto   the   ML    direction   (  p   <   0.05)   (Fig.   3B).   Alternatively,   analysis   of the   CoM   data   revealed   greater,   but   not   significant,   movement   inthe   ML    direction   compared   to   the   AP   direction   (  p   =   0.09).CoM   and   CoP   plots   for   average   sway   and   swaySD   are   presentedin   Fig.   4.   A   significant   main   effect   was   observed   when   analysing   theeffect   of    vision   for   all   variables   measured   ( F  [1,11]   =   28.27,  p   <   0.01;   F  [1,11]   =   17.83,    p   <   0.01;   F  [1,11]   =   19.03,    p   <   0.01   and F  [1,11]   =   17.50,    p   <   0.01,   respectively)   with   greater   balance   controlobserved   with   eyes   open   compared   to   eyes   closed.   Examination   of the   average   postural   sway   measured   from   the   CoM   and   CoP   timeseries   indicated   no   significant   differences   between   compressionconditions   ( F  [2,22]   =   0.18,    p   =   0.84   and   F  [2,22]   =   0.54,    p   =   0.59,respectively)   (Fig   4A).   Similarly,   no   significant   differences   wereobserved   when   analysing   the   CoM   and   CoP   swaySD   ( F  [2,22]   =   1.33,  p   =   0.28   and   F  [2,22]   =   1.63,    p   =   0.22,   respectively)   (Fig.   4B).   Asignificant   interaction   effect   was   observed   however,   betweencompression   condition   and   vision   when   analysing   the   CoM   andCoP   swaySD   ( F  [2,22]   =   3.92,    p   <   0.05   and   F  [2,22]   =   4.03,    p   <   0.05respectively).   The   interaction   effect   revealed   greater   variability   of movement   with   eyes   closed   as   participants’   level   of    compressiondecreased   (Fig.   4B). 4.   Discussion The   aim   of    this   study   was   to   assess   the   effects   of    CGs   comparedto   conventional   shorts   on   stability   during   one   leg   stance   for   60   swith   eyes   open   and   eyes   closed.   The   assessment   of    stabilityincorporated   total   balance   time   as   well   as   measurement   of    theCoM/CoP   and   deviations   from   these   points.   The   results   gatheredindicate   that   wearing   WF-CGs   significantly   improved   balance   timeand   significantly   decreased   postural   sway   variability   comparedwith   conventional   shorts   in   the   eyes   closed   condition.   However,wearing   LF-CGs   revealed   no   significant   differences,   highlightingthe   importance   of    correct   sizing   control.   Furthermore,   CGs   had   noeffect   on   static   balance   and   postural   control   when   vision   waspresent.The   removal   of    vision   demonstrated   a   significant   negative   effecton   balance   time   and   postural   sway,   which   is   consistent   with Fig.   2.   Total   stabilisation   time   (s)   for   each   compression   condition   with   eyes   openand   eyes   closed   with   their   respective   SD   values.   *Significant   difference   betweenshorts   and   well   fitted   compression   garments   (  p   <   0.05).  J.S.   Michael   et    al.    /    Gait    &    Posture    39   (2014)   804–809 806  previous   research   examining   unperturbed   stance.   It   has   beensuggested   that   vision,   as   well   as   proprioceptive   (somatosensory)inputs,   dominate   the   control   of    orientation   and   balance   [25].   Anumber   of    studies   have   also   isolated   specific   sensory   inputs   byaltering   either   vision   or   the   support   surface,   which   has   resulted   indata   that   can   be   used   as   a   baseline   for   balance   assessment   [16,25].Further,   the   reduction   of    the   base   of    support   present   in   a   one   legbalance   task   significantly   increases   body   sway   by   up   to   8   times[16]   compared   to   bipedal   stance   [14,25].This   suggests   that   theproprioceptive   feedback   extracted   when   performing   a   one   limbtask   is   not   sufficient   to   overcome   the   effect   of    visual   occlusionduring   balance   and   posture   tasks   [14].   The   results   of    the   currentstudy   support   this,   as   vision   enabled   all   participants   to   maintainbalance   on   one   leg,   irrespective   of    compression   condition,   for   theentire   60   s   time   period   with   minimal   differences   in   posturalmovement   observed.   However,   with   visual   occlusion,   the   control‘‘shorts’’   condition   demonstrated   a   significant   reduction   in   balancetime   and   significantly   greater   body   movement   variability   com-pared   to   eyes   open.   Furthermore,   wearing   the   CGs   with   visualocclusion   resulted   in   a   insignificant   reduction   in   balance   time,   withthese   values   found   closer   to   those   observed   with   eyes   open.   Thiswas   particularly   evident   when   wearing   WF-CG,   where   participantssignificantly   improved   the   total   time   they   were   able   to   balance   onone   leg   compared   to   the   control   condition.Data   analysis   of    the   maximum   absolute   CoM   movement   andCoP   displacement   in   the   AP   and   ML    directions   when   vision   wasoccluded   indicated   a   concomitant,   though   not   significant,   trend.Results   revealed   that   as   surface   compression   increased   (fromshorts   to   WF-CG),   maximum   amount   of    CoM   and   CoP   movement   inboth   the   AP   and   ML    directions   decreased   to   values   closer   to   thoseobserved   with   eyes   open   (Fig.   3Aand   B).   Although   the   largevariability   limited   the   significance   of    individual   comparisons,   asignificant   interaction   effect   was   found   between   vision   andcompression   when   analysing   the   movement   of    the   CoP.   Theresults   highlighted   the   decreased   movement   of    the   CoP   with   use   of CGs   when   vision   was   occluded.   Research   examining   CoM   and   CoPmeasures   have   found   increased   movement   with   eyes   closed   [24].This   was   suggested   to   be   due   to   greater   body   movements   in   anygiven   direction   before   movement   was   counteracted   by   correctivemuscle   action   [24].Considering   the   reduced   body   movementfound   with   use   of    CGs,   it   may   be   suggested   that   CG   use   mayimprove    joint   positional   sense   to   accommodate   for   visualocclusion,   and   thus   allowing   participants   to   improve   posturalcontrol   while   maintaining   SLS.Similarly,   following   fatiguing   exercise,   where   proprioceptionand   sensory   awareness   would   be   expected   to   decline   [26],Pearceet   al.   [11]   found   significantly   better   results   when   participantsperformed   post   exercise   visuomotor   tracking   tasks   when   wearingCGs.   This   supports   the   current   findings   that   the   compressionprovided   may   support   the   active   muscles   in   a   way   that   decreasesdependency   upon   the   visual   input   [11]   and   enhances   propriocep-tion   [27].   It   can   be   suggested   that   surface   compression   may   act   oncutaneous   mechanoreceptors   to   provide   an   additional   sensoryinput,   which   in   turn,   may   improve   sensation,   and   thus   lead   toimproved   muscle   coordination   [9]   and    joint   stability   [11].   Recentstudies   have   also   observed   improvements   in   the   stabilisation   of  Fig.   3.   Maximum   range   of    the   CoM,   CoP   and   CoM–CoP   range   differences   in   the   AP   and   ML    directions:   (A)   the   effect   of    compression   condition   and   vision   with   standarddeviations   presented   only   for   eyes   closed,   and   (B)   with   compression   condition   and   vision   grouped,   analysing   the   cumulative   effect   of    AP   and   ML    directions.   *Significantdifference   between   AP   and   MLdirections   with   compression   and   vision   grouped   (  p   <   0.05).   AP:   antero-posterior;   CoM:   centre   of    mass;   CoP:   centre   of    pressure;   LF-CG:   loosefitted   compression   garment;   ML:   medio-lateral;   WF-CG:   well   fitted   compression   garment.  J.S.   Michael   et    al.    /    Gait    &    Posture    39   (2014)   804–809   807  upright   posture   by   providing   additional   tactile   sensory   input,particularly,   using   ‘light   touch’   of    the   index   finger   with   a   stationarysurface   [28,29].Jeka   and   Lackner   found   that   contact   of    the   indexfinger   with   a   stationary   bar   attenuated   postural   sway   with   visionoccluded.   In   a   similar   way   to   the   current   study,   the   authors   suggestthat   the   pattern   of    somatosensory   stimulation   from   the   light   touchtriggers   postural   muscles   to   correct   sway.   The   current   findings   of improved   postural   control   with   CGs   together   with   those   examin-ing   light   touch   demonstrate   the   potential   applications   for   injurymanagement/rehabilitation   and   injury   prevention,   where   athleteshave   lost   varying   levels   of    sensorimotor   processes   [30].Additional   data   analysis   revealed   positional   changes   recordedon   the   force   platform   were   not   always   accompanied   by   corre-sponding   movements   of    the   CoM   (Fig.   3B).   Consistent   withprevious   research,   analysis   of    the   CoP   displacement   indicatedmovement   in   the   AP   direction   was   significantly   greater   comparedto   the   ML    direction   (  p   <   0.05)   [23,24].   Interestingly   however,although   not   significant,   analysis   of    the   CoM   data   revealed   theopposite   effect,   with   greater   movement   recorded   in   the   ML direction   compared   to   the   AP   direction   (  p   =   0.09).   To   maintain   abalanced   posture   on   one   leg,   the   postural   control   system   allows   formovements   of    the   body   segments   to   keep   the   CoM   over   the   base   of support   [23,25],which   may   explain   this   factor.   Many   perturba-tions   experienced   by   the   participants   were   accompanied   with   acounterbalancing   of    a   body   segment   in   the   lateral   direction   inorder   to   prevent   falling.   During   SLS   with   eyes   open   all   testingconditions   revealed   that   the   CoP   and   the   vertical   line   of    the   CoMare   very   close   to   alignment,   as   indicated   by   small   differencesmeasured   between   these   two   variables   (Fig.   3).   A   close   alignmentwould   suggest   a   small   sway   path,   thus   was   used   as   an   indication   of good   postural   control.   This   alignment   observation   was   recorded   inboth   the   AP   and   ML    directions.   With   visual   occlusion,   differencesbetween   the   CoM   and   CoP   in   both   directions   were   shown   toincrease.   This   difference   was   reported   as   maximal   during   the   SLSwearing   conventional   shorts,   and   again   showed   a   non-significantdecrease   as   surface   compression   increased.Finally,   the   swaySD   revealed   significant   interaction   effects(Fig.   4B).   Results   revealed   greater   variability   of    movement   witheyes   closed   as   participants’   level   of    compression   decreased.   Thedata   from   the   WF-CG   in   both   eyes   open   and   eyes   closed   were   foundto   lie   close   to   the   mean   values   recorded.   These   results   againindicate   a   greater   musculature   control   combining   with   the   action Fig.   4.   Average   postural   sway   (A)   and   the   respective   standard   deviation   (B)   for   CoP   and   CoM   time   series.   *Significant   interaction   effect   (  p   <   0.05).   CoM:   centre   of    mass;   CoP:centre   of    pressure;   LF-CG:   loose   fitted   compression   garment;   WF-CG:   well   fitted   compression   garment.  J.S.   Michael   et    al.    /    Gait    &    Posture    39   (2014)   804–809 808
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