REVISTA
BRASILEIRA
DE
REUMATOLOGIA
ww w . r e u m a t o l o g i a . c o m . b r
Review
article
Possible
changes
in
energy-minimizer
mechanisms
of
locomotion
due
to
chronic
low
back
pain
-
a
literature
review
Alberito
Rodrigo
de
Carvalho
a,b,∗,
Alexandro
Andrade
c,
Leonardo
Alexandre
Peyré-Tartaruga
aaUniversidadeFederaldoRioGrandedoSul,PortoAlegre,RS,Brazil bUniversidadeEstadualdoOestedoParaná,Cascavel,PR,Brazil cUniversidadedoEstadodeSantaCatarina,Florianópolis,SC,Brazil
a
r
t
i
c
l
e
i
n
f
o
Articlehistory:
Received23November2013
Accepted28January2014
Availableonline5January2015
Keywords:
Lowerbackpain
Humanlocomotion
Walk Biomechanics
Energyconsumption
a
b
s
t
r
a
c
t
Onegoalofthelocomotionistomovethebodyinthespaceatthemosteconomicalway
possible.However,littleisknownaboutthemechanicalandenergeticaspectsoflocomotion
thatareaffectedbylowbackpain.Andincaseofoccurringsomedamage,littleisknown
abouthowthemechanicalandenergeticcharacteristicsofthelocomotionaremanifestedin
functionalactivities,especiallywithrespecttotheenergy-minimizermechanismsduring
locomotion.Thisstudyaimed:a)todescribethemainenergy-minimizermechanismsof
locomotion;b)tocheckiftherearesignsofdamageonthemechanicalandenergetic
char-acteristicsofthelocomotionduetochroniclowbackpain(CLBP)whichmayendangerthe
energy-minimizermechanisms.Thisstudyischaracterizedasanarrativeliteraturereview.
Themaintheorythatexplainstheminimizationofenergyexpenditureduringthe
loco-motionistheinvertedpendulummechanism,bywhichtheenergy-minimizermechanism
convertskineticenergyintopotentialenergyofthecenterofmassandvice-versaduringthe
step.Thismechanismisstronglyinfluencedbyspatio-temporalgait(locomotion)
parame-terssuchassteplengthandpreferredwalkingspeed,which,inturn,maybeseverelyaltered
inpatientswithchroniclowbackpain.However,muchremainstobeunderstoodaboutthe
effectsofchroniclowbackpainontheindividual’sabilitytopracticeaneconomic
loco-motion,becausefunctionalimpairmentmaycompromisethemechanicalandenergetic
characteristicsofthistypeofgait,makingitmorecostly.Thus,thereareindicationsthat
suchchangesmaycompromisethefunctionalenergy-minimizermechanisms.
©2014ElsevierEditoraLtda.Allrightsreserved.
∗ Correspondingauthor.
E-mail:alberitorodrigo@gmail.com(A.R.d.Carvalho).
http://dx.doi.org/10.1016/j.rbre.2014.01.005
Possíveis
alterac¸ões
no
mecanismo
minimizador
de
energia
da
caminhada
em
decorrência
da
dor
lombar
crônica
-
revisão
de
literatura
Palavras-chave:
Dorlombar
Locomoc¸ãohumana
Caminhada Biomecânica
Consumodeenergia
r
e
s
u
m
o
Umdosobjetivosdamarchaédeslocarocorponoespac¸odaformamaiseconômica
pos-sível.Porém,poucosesabecomoosaspectosmecânicoseenergéticosdacaminhadasão
afetadospeladorlombar.Ainda,casohajaprejuízos,épequenooconhecimentodecomo
ascaracterísticasmecânicaseenergéticasdacaminhadasemanifestamnasatividades
funcionais,principalmentenosmecanismosminimizadoresdeenergiadalocomoc¸ão.Este
estudoteveporobjetivos:a)descreverosprincipaismecanismosminimizadoresdeenergia
dalocomoc¸ão;eb)verificarseháindicativosdeprejuízosnascaracterísticasmecânicas
eenergéticasdacaminhadadecorrentesda dorlombarcrônica(DLC)quepossam
com-prometerosmecanismosminimizadores.Estudocaracterizadocomorevisãonarrativade
literatura.Aprincipalteoriaqueexplicaaminimizac¸ãododispêndioenergéticodurantea
caminhadaéadopênduloinvertidopeloqualomecanismominimizadorconverte
ener-giacinéticaemenergiapotencialdocentrodemassaevice-versaduranteapassada.Esse
mecanismoéfortementeinfluenciadoporparâmetrosespac¸os-temporaisdamarcha,tais
comocomprimentodepassoevelocidadepreferidadacaminhada,que,porsuavez,podem
estarseveramentealteradosempacientescomdorlombarcrônica.Contudoaindahámuito
queseentendersobreosefeitosdadorlombarcrônicasobreacapacidadedoindivíduode
praticarumamarchaeconômica,poisosprejuízosfuncionaispodemcomprometer
carac-terísticasmecânicaseenergéticasdessamodalidadedemarchaetorná-lamaisdispendiosa.
Desta forma,háindicativosde quetaismudanc¸asfuncionaispossamcomprometeros
mecanismosminimizadoresdeenergia.
©2014ElsevierEditoraLtda.Todososdireitosreservados.
Introduction
The adoption of locomotion on two legs as an exclusive
formofmarchwas animportantmarker ofhuman
evolu-tion,and energysaving, inthis type oflocomotion,is one
ofthemainreasonsfortheestablishmentofbipedalism.1–3
However,the bipedallocomotioncannotalways be
consid-eredasasimpletask.Thetrunk,essentiallyunstableforits
multijointcharacteristics,maintainsits stabilityby
muscu-laractionthatconstantlymodifiesitselftoensuretheneeded
posturetomovements.4Therefore,theabilityoflocomotion
depends on a complex interaction of patterns of
coordi-natedmovementsofthehip,pelvisandlumbarspine,which,
whenharmonic,determinethenormalbiomechan-icalgait
pattern.1,5
Walkingisaformoflocomotionthatstandsoutby
influenc-ingmultipleaspectsinthephysical,socialandevolutionary
spheresofhumanexistence.6Ananthropologicaland
evolu-tionaryvisionmakesusthinkthat, ifthemodernmancan
walkquietlyandusethisabilitytoperformhisdailyactivities,
inthepastperhapsthiswasnotsosimpleforourancestors
-probablybipedallocomotionwasusedforescape,producing
tirednessandfatigue.Bipedallocomotionwasusedtopermit
man’sflight,causinggreaterexhaustionandfatigue.
Through-outtheevolutionaryperiod,certainanatomicalchangeswere
occurringslowly over thousandsof years,toallowthe
fix-ationofthis modeofmarchandpromotingadaptationsof
humanlocomotorsystemthatprovideuswithperspectives
on musculoskeletal disorders found in the current clinical
scenario.7
The biped march encompasses many aspects that go
beyondasimpleactofplacingoneleginfrontoftheother.
It can be understood as a cyclic movement with loss and
recoveryofthebalance,duetotheconstantchangeof
posi-tion ofthe bodycenterofmasspromotingbody instability.
Suchinstabilityiscompensatedbylegmovements,ranging
fromastancephase,whichcanbesingle-legorbipedal,and
a swingphase, inwhichthe legisfreeintheair. Thus,at
the end ofthe swing phase, the center ofmass lies in a
posteriorrelationtotheanteriorlyextendedlegandbegins
to rise, due to the kinetic energy,at the beginning of the
stance phase, after the heel contact with the ground (i.e.,
heel-strike). During the first half of the step, the kinetic
energy decreases asthe center ofmass gains height,with
consequent increase ofpotential energy which reaches its
peak in the middle of the one-leg support phase. In the
second half ofthe step, theopposite occurs; the centerof
masslosesheightandthepotentialenergyisconvertedinto
kinetic energy. The reconversion between the mechanical
energies connected to the center of mass during walking
plays a crucial role in the individual’s ability to walk as
economicallyaspossible,andisinfluencedbyanumberof
spatio-temporalgaitvariables,suchassteplengthandgait
speed.8–11
Theimpairmentofthenormalgaitcycleandthelossof
characteristicsofenergyconservationbetweentrunkandlimb
movementsresultingreaterenergyexpenditure.Patientswith
diseasesthatcompromisetheabilitytowalktendtodevelop
compensatorygaitpatternstominimizetheadditionalenergy
Lowbackpainisacommonsyndromeworldwide,
generat-ingrelevantsocioeconomiccosts.Accordingtoestimates,80%
ofpeoplewillexperienceanepisodeofthiskind ofpainat
somepointintheirlife.Lowbackdisordersaremultifactorial;
and pathologic, physical, neurophysiological, psychological
andsocialfactors haveadifferentimpacton each
individ-ual,andinabout90%ofcasesitisnotpossibletopinpoint
thecause ofthe dysfunction,whichcharacterizesthe
non-specific low back pain picture. Despite the limitations to
establishtherelationshipamongclinicalcharacteristicsand
theconditionscausinglowbackpainwiththeeffectiveness
oftreatmentprocedures,it is observedthatbiomechanical
andphysiologicallossestendtofollowchroniccasesoflow
backpain.Many oftheselossesare identifiedinthe
litera-ture,suchasdecreasedspeedofacomfortablegait,decreased
steplengthandswingtime,12,13 decreasedmaximalaerobic
capacity,14decreasedresistanceofthelumbarextensorswith
consequentanteriordisplacementofthecenterofmass,poor
posturalcontrol,15,16incoordinationofthepelvicandthoracic
rotations,17 delayintheplanned activationofthe
transver-susabdominis,andimpairedrelaxationphenomenonduring
trunkanteflexion.18,19
Ina study thatidentified the mainactivitiesperformed
withdifficultyintheperceptionofpatientswithchroniclow
backpain,itwasobservedthat56%of101volunteersreported
lowtoleranceto walkingas oneofthe fiveactivities more
poorlyperformed,thisbeingthemostprevalentiteminthat
sample.20However,ourknowledgeitisstilllimitedabouthow
themechanical and energeticaspectsoflocomotion,
espe-ciallywithrespecttogait,areaffectedbylowbackpainand
howthedamagesresultingfromitsoccurrencearemanifested
in functional activities, mainly with regard to the
energy-minimizer mechanisms of locomotion. The understanding
ofthese issueswouldbeanimprovementtoexplainifthe
changesobservedduringwalkinginthispopulationaredue
totheinabilityofthebodytoprovideaneconomicalgait,orif
theyexistpreciselytopreservetheseenergy-minimizer
mech-anisms.
Thus,this studyaimed: a)todescribe themain
energy-minimizermechanismsoflocomotion;b)tocheckifthereare
signsofdamageformechanicalandenergeticcharacteristics
ofgaitduetochroniclowbackpain,whichmayendangerthe
energy-minimizermechanisms.
Method
Thisstudywascharacterizedasanarrativereviewof
litera-ture.Weconductedaliteraturesearchinelectronicdatabases:
Capes,PubMedand SciELOarticles,writteninEnglish,
Por-tugueseandSpanishlanguages,listedfromtheintersection
ofthefollowingkeywordsinEnglish(lowbackpain,human
locomotion, walking,biomechanics, gait, energy
consump-tion)andtheirequivalents inPortugueseidiom(dorlombar;
locomoc¸ãohumana;caminhada,biomecânica,marcha,consumode energia) in a search period delimited from 1998 to March
2013; as well as classic articles related to the subject,
cited in the references of those previously selected
arti-cles.
Energy-minimizer
mechanisms
of
human
locomotion
Thenormalhumangaitcanbedefinedasthemarchmodality
thathumansusetomoveatlowspeeds.Thegaitcyclecanbe
understoodasthetimeperiodbetweentwoidenticalevents
inthewalkingprocess,andthisfullcycleisdividedintotwo
phases:stanceandswingphases.21
Thestance phasebeginswiththefirst contactofafoot
(usuallytheheel)withtheground,endingwiththelast
con-tactofthesamefootwiththeground,correspondingtohallux
take-off.Theswingphasebeginswiththelastcontactofthe
footwiththeground,endingwiththefirstcontralateralfoot
contactwiththe ground.Duringthefirsthalfofthe stance
phase,thereisadecreaseinthevelocityofthecenterofmass
untilthemidpointisreached;ontheotherhand,inthe
sec-ondhalfthecenterofmassincreasesitsspeedagain.During
thestancephase,thelegremainsextendedandthemidpoint
ofthisphasecoincideswiththehighestpointofthetrajectory
ofthecenterofmass.8–10
Complexphenomena,suchasgait,inwhichmany
vari-ablescontributetotheiroccurrence(someofthemdifficultto
quantify),maynotalwaysbeamenabletostudiesinreal
con-ditions.However,insomefieldssuchasbiomechanics,these
phenomenaaresimplifiedintheformofmodels,whichcanbe
mathematical,physicalorconceptualones;andsuchmodels
allowustounderstandthephenomenonmorebroadly.22,23
Although contradictory, thereare two theories(models)
reportedinstudieswithrespecttomarchthatseektoexplain
themechanismsbywhichthisphenomenoncanbemore
eco-nomical:thetheoryofsixdeterminantsofgaitandthetheory
ofinvertedpendulum.Themaindifferencebetweenthetwo
theoriesresidesinthetrajectoryofthecenterofmass.23
Thelessacceptedisthetheoryofsixdeterminants,which
proposesthatasetofkinematicfeatures,suchaskneeflexion
atthetimeofstanceandpelvicrotations,amongothers,are
usedstrategicallytopermitthatthecenterofmassofthebody
describeastraighttrajectoryduringwalking.Theargument
forsuchbehavioristhattheverticaloscillationsofthecenter
ofmassgenerateanadditionalenergyexpenditure,duetothe
needformusclecontractiontospeeditupandliftitagainst
gravity.Themaincriticismofthismodelisthat,tominimize
theenergyexpenditureassociatedwiththeoscillationsofthe
centerofmass,itcreatesaneedforthelegsremainingbent
inthemostpartofthestep,andthat thishasmorecostly
energeticconsequences,incomparisonwiththeoscillations
ofthecenterofmass.23
On the other hand,the theory ofinverted pendulumis
the more accepted, being usedin the studies.Thehuman
march,onlevelgroundandunderabiomechanical
perspec-tive,resemblesa“rollingegg”oraninvertedpendulum;these
analogiesdescribethebehavioroftheenergychangesrelated
tothecenterofmassofthebody.Mechanicalmodelsthat
rep-resentthebehaviorofthebodycenterofmass,understoodas
theexternalworkdonetoraise/loverandaccelerate/delaythe
centerofmassinrelationtotheenvironment,havebeenused
toexplainhoweachtypeofgaitemploysandsaves
canalso beseen asarigid segment model),when applied
togait, the kineticand potentialenergies change interms
ofphaseopposition(whileoneofthemreachesaminimum
value,theother reachesa maximumvalue) duringcontact
withthe ground in the unipodal phase, allowingan
inter-changebetweenthetwoenergies.Thismodelproposesthat
themasscenterdescribesacurvilineartrajectoryduringthe
step(similartoapendulumpositionedupsidedown)andthat
thelower limbthatsupportstheweightbehavesasarigid
segment.Inaddition,thismechanismofenergyfluctuation
reducesthemechanicalworkimposedbythemuscular
sys-tem,thankstotheenergyconservation;and thisreduction
isproportionaltothebody’sabilitytoreconvertoneenergy
typeintoanother(i.e.,kineticenergyintopotentialenergy,and
vice-versa)–amechanicalfeatureknownasrecovery.8,10,24,25
Thus,the actofwalking withthe kneeextendedinthe
stancephaseappearstoresultintwoadvantages:inaddition
toprovidingtheverticaldisplacementofthecenterofmass,
facilitatingenergyconservationthroughexchangesbetween
kineticandpotentialenergy,alsoallowsthattheactionline
(vector)ofthebodyweightpassnearthelowerlimbjoints,so
thatthereislittleneedformuscleactiontopreventthatthese
jointssufferfromtheirimposedloads.Thesetwoconditions
favorenergyconservation.26
Thependulum transductionbetweenkineticand
poten-tialenergiesreducestheexpenditureofchemicalenergyfrom
both the positive muscle work (that required to increase
potentialandkineticenergy)andnegativemusclework(that
requiredtoreducepotentialandkineticenergy).Thefraction
of reconverted mechanical energy due to pendular
trans-duction (recovery – %R) is defined mathematically as: %
R=100 (W+
f+W+v – W+ext) / (W+f+W+v) whereW+f is the
positiveworkcalculatedfromthesum,throughoutthestep
cycle, of the positive increments promoted by the
previ-ousdisplacementduetohorizontalkineticenergy(CEh=0,5
MVh2,whereM=massofthebodyandVh=theinstantaneous
horizontal velocityof the center of mass); W+
v represents
thepositivework calculatedfrom thesum,throughoutthe
step cycle, of the positive increments promoted by the
verticaldisplacement dueto gravitational potential energy
(PE=Mgh, whereM=body mass,g=the accelerationdue to
gravity and h=the instantaneous height of the center of
mass);+Wextisthepositiveexternalworkcalculatedfrom
the sum, throughoutthe step cycle, ofthe positive
incre-mentspromotedbythetotalmechanicalenergyofthecenter
of mass (Emtot=PE+CEh+CEv, where PE=potential energy,
CEh=horizontal kinetic energy, and CEv=vertical kinetic
energy).CEv(CEv=0,5MVv2,whereMv=instantaneous
verti-calspeed)hasbeenneglectedinthiscalculation,becauseit
doesnotinfluenceW+
v,sincetheverticalvelocityiszeroatthe
topandatthevalleyofthepotentialenergycurve.Thus,the
recoveryrepresentsthemaximumfractionofpositiveenergy
incrementslinkedtothecenterofmassthatarereconverted
bythependulummechanismthroughoutthestepcycle.10,27
Inanidealpendulum,the energyexchangeiscomplete
(energyrecovery=100%).Nevertheless,inthehumangait,the
energyrecoveryismoderatelyhigh(upto60%)anddependson
thesteplengthandwalkingspeed.Recentliteraturesuggests
somecontributionofelasticenergytothemarchmechanisms,
bystoringthisenergyanditsreleasingintheAchillestendon
andpossiblythroughthearchofthefoot.Theparticipation
of elastic energyduring gait isaccepted by someauthors,
althoughthiskindofenergyhasanapparentlymoredecisive
participationintheraceactivity.10,28,29
Duringthelocomotion,thegaitparametersareadjusted
sothattheforce,work,powerand/orenergyexpenditureare
minimized.Thus,duringgaittheaveragemechanicalpower
isminimal,whenthesubjectiswalkingonastepfrequency
closetothatfreelychosen(self-selectedspeed).
Correspond-ingly,theoxygenconsumptionisalsominimizedatthesame
frequency.30
Undernormalconditions,thepowerconsumptionofgait
(metabolicpower–consumptionofoxygenperkilogramof
bodyweightduringagiventime)isrelatedtotheintensityof
effort,andcanbeaffectedbychangesinspeed.Thus,speed
isacrucialmeasure,beingdeterminanttoenergy
expendi-tureinwalkingtests.Theinfluenceofspeedissorelevantto
energyconsumptionthattheoxygencostpermeterwalked
(aconceptcalledthetransportationcost)isobtainedbythe
ratiobetweenmetabolicpowerandspeedofwalking,being
indicativeofthequalityofthewalk.9,31
Transportationcostisameasureoftheeconomyof
loco-motion and represents the amount of metabolic energy
consumed tomove onekilogramofbody massper unitof
distance, beingexpressed as J.kg-1.m-1 10,32 and provides a
metabolicinformationofgaitquality.Putmoresimply,
trans-portationcostcanbedefinedastheforcerequiredtomovea
unitofmassbyaunitofdistance.
Thetransportationcostvariesdependingonthespeedwith
whichthemarchisheld,beingusuallylowerinself-selected
speedsforeachgaittype.Basedonthis,Margaria,inthelate
1930s,proposedthatthecurvesoftransportationcostinterms
ofspeedtooktheformof“U”,becausethefartherthe
stud-iedspeedwithrespecttothatself-selectedspeed,thegreater
thetransportationcost.10,33Infact,theoptimalwalkingspeed
has been defined insome studies asthat speed in which,
simultaneously,thereisoptimizationofthecontributionof
mechanicalparameterscharacteristicofthistypeofgaitand
alowermetaboliccost.34
walking at higher speeds than the self-selected one
requiresanincreaseintheactivityofthosemusclesinvolved
inpropellingthebodyforward,beingalsoassociatedwitha
greatersteplength,whichincreasestheactivitybothofthe
musclesthatcontributetolegswingasofthosethatcontribute
totheverticalcontrol,sincetheverticalexcursionofthe
cen-ter ofmassofthebody alsoincreases. Conversely,walking
atlowerspeedsbecomesmechanicallylessefficient,because
thereisgreaterneedforstabilization,andonecanrelylesson
theelasticenergyofthemuscleandtendonunits.35
Consequently,onemightthinkthatthereisaparallelism
betweenenergeticandmechanicaspectsofhuman
locomo-tion.However,becauseofitscomplexity,manyfactorsmustbe
takenintoconsideration.TaylorandHeglund36showedthat
observed changesinmetabolic power,dueto thevariation
ofspeedandbodyweight,didnotresultinparallelchanges
inthemechanicalworkdonebymuscles.Theseauthorsalso
suggestthatthemetaboliccostofgeneratingmuscularforce
during the foot-and-ground contact, regardlessof whether
the mechanical work (product offorce bydisplacement) is
concentrations),iswhatdeterminestherateatwhichenergy
isconsumed.ShiandStuhmiller37concludedthat,formany
activities,thereisarelationshipbetweenmetaboliccostand
themagnitudeandfrequencyofforceapplication,linkedto
theeffectivecontacttimeofthefootwiththeground.
Verydifferentchanges instepfrequency,incomparison
withthatconsiderednatural,caninducesignificantchanges
in energy-minimizer mechanisms in walking. At a given
speed,therecoverypercentagetendstoincreasewhenthe
steplengthisgreaterthanthatobservedinthenaturalgait
and,conversely,tendstodecrease whenthe steplengthis
smallerthanthatfreelychosen.38
Thetrunkcoordinationduringthehumanmarchhasalso
been a focus of study.In normal subjects, the increase in
walkingspeedchangesthephasicrelationshipbetweenthe
rotations of the trunk and pelvis in the horizontal plane,
sothatatlowerspeeds thesetwosegmentstendtohavea
moresynchronousbehavior(in phase),that becomesmore
andmoreasynchronous(outofphase)asthespeedincreases.
Thus,inabriskmarch,theoscillatorymovementsofthetrunk
inrelationtothepelvisbecomemoreevident.Althoughthe
mechanismsthatgovernsuchcoordinationarestillnot
com-pletelyunderstood,eveninnormalsubjects,insomedisease
conditions–suchasinlowbackpain–thereisalossofthis
coordinativemovementinawaythat,evenforhigher
walk-ingspeeds,bothsegments(trunk andpelvis)tendtomove
synchronously,forcingamore“enbloc”styleofwalking.39,40
Mechanicalandenergylossesduringgaitarisingfromlow backpain
Whilenormalsubjectsselecttheirlengthandfrequencyof
stepsinorder tomakethe mosteconomicalgaitfrom the
pointofviewofenergy,thosewithdiseasesinvolvingthe
loco-motorsystemchangethatstrategy.Largesteplengthsinduce
changes inthe system ofcoordination between trunkand
pelvis,implyinglargerrotationsbetweenthesesegments
dur-ingwalking.Inpathologicalmarches,thereisatrendtoavoid
largeoscillationsofthecolumn,andtheseindividualscando
thisinseveralways;astochroniclowbackpainpatients,they
tendtowalkmoreslowly,decreasingthelengthand
increas-ing,toalesserextent,thefrequencyoftheirsteps.40
Subjectswith lowback painexhibit several adaptations
duringwalkingasaresultofpain,suchas:alterationof
pro-prioceptiveposturalcontrol;stiffertrunkandbodystrategy,
leadingtotheadoptionoftheanklestrategy;increased
activ-ityoflumbarmusclesduringallstepperiodsand,secondarily,
lessrelativerelaxationduringswingperiods,comparedwith
double-stanceperiods;adecreaseoftheverticalcomponent
ofgroundreactionforcesinthoseindividualswhosepainis
radiatingtothelowerlimbs;adecreaseinpreferredwalking
speed;adecreasedthorax-pelviccoordinationinthe
trans-verseplane,inducinga morerigidbehaviorbetweenthese
segments; a shorter step length, among others. Moreover,
patientswithnonspecificchroniclowbackpain,whenasked
toincreasetheir walkingspeed,tend toincreasemorethe
cadence,ratherthanthelength,ofthesteps,unlike
individ-ualsfreeofpain.15,41-45
Lamothet al.44 observedthatindividuals withlowback
painwhowalkedinthesamerelativespeed(110%ofpreferred
speed)ofsubjectswithoutlowbackpainshowedsteplength,
walkingspeedandsteplengthvariabilitysignificantlylower,
butthiswasnotobservedwhenthestepfrequencywas
eval-uated.Elbazetal.46observedthatpatientswithnonspecific
chroniclowbackpainshowedasymmetryintheirone-foot
supportandinswingandstancephases,inadditiontoalower
walkingspeed.Theseauthorssuggestthat,inthesepatients,
thedecreaseinwalkingspeedcanbeunderstoodasa
protec-tivemechanismattributedtoanattempttoreducetheground
reactionforcesandtominimizetheoverloadinthecolumn
andavoidpain.
Thepain,atleastwhenitcomestowalking,seemstoplay
amoreimportantroleinacuteepisodes.Moe-Nilssen,
Ljung-grenandTorebjork47triedtofindoutifthemeasurementof
thelumbarspineacceleration,quantifiedbyanaccelerometer,
couldindicatechangesinmotorbehaviorduringwalking,as
aresultofatransientlowbackpainexperimentallyinduced
byaninjectionofhypertonicsalineintothelongissimusdorsi
muscle.Theseauthorsfoundadynamicinteractionbetween
pain and adaptation in motor performance, when
observ-ing reduction of lumbar acceleration during the period of
maintenanceofinducedpain,assumingthatthischangewas
processedbythevegetativenervoussystem.
Taylor,EvansandGoldie48comparedagroupofvolunteer
subjectswithacutelowbackpainsevendaysaftertheonsetof
painandsixweekslater,whenthepainhaddisappeared,and
alsoevaluatedsubjectswithoutlowbackpain.Ineach
assess-mentall participantswalkedattheself-selectedspeed and
atanintensity40%fasterthantheself-selectedspeed.These
authorsobservedthat,athigherspeeds,duringtheperiodof
exacerbationthelumbargroupexhibitedsignificant
adjust-mentsinthewayofwalking,suchasincreasesinpelvictilt,
inlateralflexionofthelumbarspineandinthesteplength
ver-suspost-testevaluation.However,nodifferencesinrelationto
thecontrolgroupwerefound.Thesefindingssuggestthatthe
paincancausechangesinwalkingstyle.
In chronic pain conditions, an understanding of the
adaptative processesbecomes amuchmorecomplex task.
Accordingly, otherstudies alsoshift thefocus ofpain asa
determinantvariableinthepopulationofchroniclowback
painpatients,attheexpenseofthefunctionalpicture.The
evidencesuggestingthatsupraspinalchanges
(neurodegen-erationofdorsolateral portionofprefrontalcortex; gradual
decrease in neocortical, prefrontal cortex and thalamus
graymattervolume,amongothers)presentinpatientswith
chronicnonspecificlowbackpainmay containthe
mecha-nismsthatjustifytheclinicalfindingsisincreasing,although
still without consensus about this supposition. Thus, it is
believedthatthisreorganizationwithinthebrainiscapableof
generatingapictureofpersistentpain,evenintheabsenceof
physicalchange,andthisincludesthecortical
neurodegener-ationanddescendinginhibition,producinganabnormalstate
ofsensitivity;memoryofpain;andgenerationofcentralpain
asaresultofsensorimotorincongruence,whenthepatient
ismoving. Therefore,the motorchangesobservedinthese
individualswouldhaveacentral,ratherthanperipheral,
ori-gin,andthisknowledgeimposestheneedtorethinkboththe
natureoftheproblemasthebestwaytoapproachit,because,
byallaccounts,thephysicalchangesceasetobethecause
representationandintheattemptsofthepatienttomaintain
the same functionality,even inthe presenceofa changed
bodyimage.49
Otherstudieshavealsoconfirmedthechangesinvolume
anddensityofthecortexaswellasofthewhitematteramong
patientswithchroniclowbackpain.50-52Thesechangeswere
observedinseveralcorticalareas,includingthoserelatedwith
thespeedofgaitprocessing,asthecorpuscallosum,which
alsoseemstobeassociatedwithpoorphysicalfitnessand
durationofpain.51Thestructuralandfunctionalchangesthat
occur inthe brainoflow backpain patients, suggestedby
thesestudies, giveduecredit tothe hypothesis that these
individualsareless abletoadapttheirspatio-temporalgait
parameters,incomparisonwithpain-freeindividuals.
Con-sequently, as the gait kinematics plays an important role
inenergy-minimizermechanisms,thehypothesisproposing
thatthesepatientsarealsoless economicalbecomesmore
robust.
Thus,itisimportanttoidentifywhetherthechanges
dur-ing gait, observed in this population, arise also from the
inabilityofthebodytoprovideaneconomicalgait,orifthey
existpreciselytopreservetheeconomyofgait.
Atleastwithrespecttothescopeofthisliteraturereview,
nostudiescorrelatingthemotorlossesinlocomotion(widely
describedamongchroniclowbackpainpatients)with
energy-minimizermechanismsofwalkingwerefound.Therefore,this
suggeststheneedforstudiesthatseektounderstandwhether
ornotthereisalossofthesemechanismsinthispopulation.
Final
considerations
The main theory explaining the minimization of energy
expenditureduringwalkingistheinvertedpendulum
mech-anism,andtheenergy-minimizermechanismofthistheory
would be the reconversion that occurs during the march,
among the mechanical energies linked to the body
cen-ter of mass (kinetic and potential energies). However, this
energy-minimizer mechanism is strongly influenced by
spatio-temporal parametersofgait which, inturn, may be
severelyalteredinthoseindividualswithchronicbackpain.
Thus, there isevidence that such functional changes may
compromisetheenergy-minimizermechanisms.
Conflict
of
interests
Theauthorsdeclarenoconflictofinterests.
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