The relative effectiveness of hip and ankle balance strategies

Abstracts

I Gait & Posture

The Effect of Bradykimsin on FWstural Contrd and Stability Lhuis Quiet Statding Francesco ‘, R. Mecwi. E. Benvenuti. I. Cinepmri, S. Bandinelli, L. Fermcci, M. Rabuffetti. A. Baroni. I. Del Long”, M. Hallettt, S.J.Stanhopet U.O. di Geria,na, Ospedale INRCA “I Fraticini”. Florence, Italy tNa.tionel Institufes of Health. Bethesda. MD, USA Intmduetton Slowness of movement (bradykinesia) is one of the characteristic features of Parkinson’s Disease (PD). It is believed lo result from imoairments in the ability to energize skeleral muscle volonmrily (1.2). Balance conuol is coo&red a complex mot”; skill &requires the mtegration of sensory information and the planning and execution of movement patterns m order to achieve postural goals (3). Qoie, standing has the apparent goal of creating sLlbih,y by minimizing motion of the body’s center of mass (COM) over Ihe base of support. This IS typxally accomplished by the coordinated activation of postural muscles about the ankle Joint for sagittal plane and the hip join, ab/adductors for froMal plane convol. The center of pressure (COP) locaoon is indrcative of the ne, activatron of postural muscles. In addition, the difference between COP and COM locations is directly related ,” muscle induced accelerations of the COM and therefore postural comml (4). The purpose of this study was ,” evaluate the effect 01 bradyklnesm on molar control (COM-COP relationshm) and stability (COM sway area) during q;ie, sunding MdhOdOlO~ Bmdykinesia seventy and posrurography a~sessmenll were performed on nmeteen patlen& wth PD (12 males. 7 females; aged 71.3_+6years) and 43 healthy control subjecu (22 males and 21 females, aged69.326 years). Kinetic and kinematic data were obtnned simultaneously (5Ohz) from P Kisder force platform and a four-camera ELlTE system (4.5). Sevenry of bmdykinesir was deermined from the mean venical velocity of a target losated over the lif,h me,a,arsal head obtained from a 1.5s task m which the seated SuhJecu were asked ,” reoeuedlv Alex and exteod their ankle )“m& “as fast as possible.” The normal sublet, data (mean - ;w” slandard deviaooos) were used ,o diode the PD subject group mt” ,w” subgroups: mdd (n=lO), and moderate (n=9) levels of brddykinesln Donng posmragraphx ,eslmg, sublects were requesld 1” sraod “as still as possible” on Ihe torte platform for 40 seconds. A 15s m,erval of data was enuacted from the middle of each ma1 and andyned. Three mdependen, variables: viwon (eyes “pen, EO. or closed, EC), fool pmpr~ocepu”” (firm surface or comphan, surface), and base-ol-suppon size (fee, apan tar large base or together ,“r nxr”w b&e) were combined 1” produce eigh, quiet sending ,est condmons of varylog dik~xuhy (5) The followmg dependent vartables were measured: I) whole body COM sway area I” the honzontill plane (COM-AREA), 2) COP mean velocity (COP-VEL). 3) Correlaoon coeffic,en,s between COM and COP Ioc~Im”s I” the anten”r/pos,enor (COMICOP-AP) and medial/la,ernl (COMICOP-ML) drrecdons. ANOVA models w,h repeatedmeumes (p ‘: 05) were used 1” determine dlffenwces between groups and condiuons ReSUlb Mean ~elo~~l~es(mm/s) of loo, movemenu were 1511.X~35.15,Il4.7+33 28. and 59.4il5.25 respecovely for the normal, rmld and moderate gr”ups. Compared 1” Ihe normal subjecls. the cumhmed palient groups presrnted grea,er poswrdl instdbrlity (COM-AREA) in all bu, two of Ihe test condmons. COP-VEL was htgher in the PD group under the e&es, condiuons but faled t” mcrease hke the normal group acmss m”re difficult conditions. The normal group also demonsrramd greater dynamic ankle conirol (lower COMICOP-AP values) than the PD paoenw m the mos, dlfficutt con&lion only (eyes closed, comphant surface, narrow base). The rmld vs. moderaw bradvkmesra prow comparrsons revealed a s&ingly dlffercnt resuk. COMICOP-AP was the only dependent variable that dlffercd between the palie”, groups. The ~“rrelatlon of COM and COP in the amenor posterior duecoon was lower for the rmld group under dll comph”, surface condltlons and only one (eyes closed. large base) hrm surface condition. Plgure 1 contams plols of COM-AP and COP-AP from ,hrce represemauve sublrcts during the mos, dlfficul, lask (eye& closed. comphao, surface, narrow base) Tbc customary ,,uc,ua,~ms of COP about ,he COM arc reduced m amphtude and frequency 1” the graph fmm the mdd s”bJec, data. These rcductrons continue m the moderate sublea and several phase\ ot a saw toothed pattern ol COP (whoul crossmg (‘OM) become pre\dlen,

7 (1998)

144-190

The Relative Effectivenew of Hip and Ankle Balance Scrategis N Harden. M.E.. S. Stanhope.PhD T Kcpplc. M A Bmmechanrcs Ldhordtory, Ndlion~l Insu,u,e~ oi Hcahh. Bethesda.MD

1ntmducti0n Mamtamn~ slandmg halancehas beenexpressed .a Lheabrl,,y m mamtam ,hc body center of mass (COM) wr,hm ,he hue of suppo” (BOS). Stanhopee, al (I) delmed mdmtenance01hdlnnce its ,he dhrhty 1” rmplemem B w&egy ,hat produced a dewed change I” hody s,a,e such tha, lor a gwen se, ol~condmons.the hody COM would he malntarned whm the BOS. The magnules of net muscular momems generated,o produce changes m body swe, I e positron and velowy. delined Ihebalance s,mtegy. There has heensome dcbntc regarding Ihe role 01Lhehip andankle ~“mu m conlmlhng upngh, balance Ku” er al (2) incorporated a four hnk segment model ,” study the effect of instantaneoussamttd plane hip, knee and ankle momen,s o” accelem,rons of ,he COM. Cnmhmauons of &kle and hip/ankle instanmoeousne, muscuhu momenll were evdluawd and it wils concluded th;it boih joints were effectwe m accelerating the COM. hut ,hal ,he hip moments required less neural effor, for L gwen magnitude of horizontal COM accelerahon. Kepple et al (3) recently interpreled htp and mkle control of Ihe HAT throughou, free ambulatronand found that the anMe swxegy was most effective I” accelerabng lbe COM hut the effectiveness of joint momems chaoged dramatically over time. Stanhope(I) determineda” envelope of dynamic balance for which the time c”wse of a” ilnkle s,ra(egy could maintin upright balance for a given se, of mpm body accelerations. The mpu, acceleralions were venfred experimentally To dare. ule net effectiveness of &mate halancestrategies has ye, to be determined over their entire ome course. Therefore, ,he purpose of this study was 1” compare the net effccweness of entire hip and ankle ,“mt balancesw&gxs m maintaming uprIght balance

MNJWdS A planar two-hnk segment slmulabon model, conswmg of lower exvemmes and a head/arms/thorax (HAT) segment, was used to esomate the maximum capacity of ankle and lup svategies 1” mam,zu upngh, slanding balance. Model anthropomemc characlenstics (segment lengths and memti pmpenies) were dewed. Hip and tie Joinu were modeled as fnctionless pmned-hinges Jomt momems were gwen “instao, on” charactenstlcs. and were estimatedusmg model physical characteristics and system slate dynamrcs. All movement wu assumed to be bilaterally symmenic and in the sag&al plane. All simuiar~onswere staned with Ihe model sunding upright andno hip joint angular velocity. initial ankle join, angular velocities were systematically increased after each successful balance recovery until the strategy being evaluated was no longer capable of maintaining the COM within the BOS. The ankle strategy consisted of a one degree-of-freedom (fixed hip) invened pendulum under sole convol of the ankle jmm musculature. Ankle m”menu were demrmmed as the equilibrium moment that would prevent the feet from muting abou, the maximum anterior excursion of the COP. The hip sVa,egy consisted of a bi-phasic moment panem tha, beganwilh hip flexion m”menrs and traositioned 10hip extension momems - the laner required 10 stop forward mtation of the HAT segment. The transition of hip momems fmm flex~on 1” extension WBScommlled using a mono-exponenual function. The exponential function was ramped when the hip angle reached 5 degreesof extension and the ramp time was set lo 0 05s. Opomal lop s,ra,egy parameters were pre-selected usmg d txld search me,hod

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Discussion Wlule I, appears fhat ,he presence of PD g o ledds 1” a decrease m qmc, sunding 4 statxhty and allered m”,or cnntml $-I0 strategm. an m~rcese m ,he level of hradykmesu did not resuh m a decrease m 2&Q samp(s 499 748 poseral slaixhty Hnwever, ditferences I” ’ COMICOP-AP ,hal Were revealed durl”g Figure 1. A,P COM md COP locdtmns ,he more demandme cusfuon rurfacc condmons suggesl hriykmesla resoI,.\ I” altered mow control s,ra,cg~cs tlu, may Referewes become 11% etlecuve during more I) Hdlettct al Brorn 1(13:301-314.19x0 demandmp posmrdl tdsks fheretorc, we 2) Baronr e, al. Nrur” 34:X68-876. ,984 conclude ,hat the d&c, “1’ reduced 3) Homk G & P6:76-84, I9?J7 postural muscle snergiring IS il palho4) Wmler G&P 3:193-214. 199s physmlotxdl mechamsm of posmrdl 5) Benvenu,~et al. G & P 5: I R5-I X6. ,997 msrnhd~ty ?nPD Acknowledgements Thm work was sponsored hy ,he Ld,un Mmstry of Hcallh and recewed generous techmcal suppo” by BTS s p a

R.S”ltS The mmm~um mmdl toward velocw ot the COM lha, could he reversed or,or D ,he COM pitsung “u,.vde ,he BOS wu 0.11 m/s’@5 de@ a, ,hc ankle ,“m,, Ior ,he h’lp swegy and 0 45 m/s (2X 0 deg/s a, ,he ankle ,om,) for the lntle strategy. Evaluaong these eweme cases funher, I, took 1.0 set tor ,he ankle strategy 1” “verc”me the “noal COM velocrly (1.45 m/s whde it took 0.5s ior rhe hip suategy 10“vercome the mr,rdl COM velocily 0. I1 m/s. A, ,he compleoon of thesesimulations. the ankle switepy placed ,he ankle ,mnt to,” 8 degrees“, dorsl flexron whde rhe h,p strategy flexed the hlp Aih&ees and planlar ilexed the ankle IS degrees The tigure helow c”n,ams a prolile ot the resuhmg COM accelerate”” Ior each strategy The ontial ixp tlexlon mom&. created by the hrp~srrategy,produced a postertor (negalwe) accelerdlion of the COM (maximum value of -3 30 m/s/s). COM Accelerations This was rmmedmlely c”unteracted by an antenor accele&n of the IIIOXI~“~- the m”me”, mqmred lu stop the HAT tram rolanng forward. The ankle s,ra,ew created a c”nlm”“us post&or accelerauon of ,he COM whrch slowly decayed from a” mmal value of -1.45 m/s/s 1” a mmtmum value of 28 m/s/s. A net “effect” of each s,ralegy was computed as a product of Ihe average COM acceleration and the time duration of the imposed svategy. The net effect of the hip svategy was 14 m/s for the hip svategy and -0.51 for rhe ankle ?.,rategy. The difference m the two net effects corresponds 10the driference tn inhal COM velocrty for whxh each srrategy was able 10compensate

Discussion

The resulls of dus study qmte clearly mdicate duelimoaoons assocmted wth detimnp balance sUa,egiesusing insranr~eous join, m”vemenrs or “et muscular forces as descriptors While hip join, m”menu are cleafly capable of producmg far greater insrarmmeousacceleral~onsof the COM than ankle momqnts, the net effecl of the hip svategy was clearly inferior to dx capabilities of the aokle stitegy. To s~ess this point for&r. 1,,s imponao, Lonote that Ihe ankle suategy was capablepf reversing the maximum velocny condition (0.1 I m/s) for !he hlp strategy I” 0.08s as compared 1” the hip svategy taking .5s to reverse Ule same mioal velocny.

Referencw (I) StanhopeS. Cur dr Posrure 4173.174, ,996 (2) Kuo Ae, al. JoumdofBiomchonia 26(1):137-150. I993 (3) Kepple T et al. Gait & Posture 61-8. 1997.