Balance Performance on the postural stress test Comparasion of youg adults, healthy elderly, and...

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1990; 70:410-415.PHYS THER.StudenskiJulie M Chandler, Pamela W Duncan and Stephanie AFallersComparison of Young Adults, Healthy Elderly, andBalance Performance on the Postural Stress Test:

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esearchReporfBalance Performance on the Postural Stress Test:Comparison of Young Adults Healthy Elderly and Fallers

Theputpose of thI3 study was to compare the postural responses of thee groups ofindiuid~ak--healthyyoung adults (n 42; age, 20 40yean); healtby,community-dwelling elderly indiuiduak ( n 66;age, 60 102 years), and elderlyindiz/idLak with a history offrequent alls (n 10; age, 6 6 9 5yean)--using thepostural stress test (PST). i%e PST is a simple, clinically appliulble, quuntitativemeasure of an individual's ability to withstand a series of graded destabilizingfwces applied at the level of the subject5 waist. Elderly fallers tend to score loweron the P T han elderly nonfallen, but age-related d@wnces in pasturalresponses during the PST bate not been established. Each subject uundenvent thePST using a method and scoring procedure desm'bed preuiously. Results of thisstudy con m previous findings that elderly fallers score sign@cantly lolver on thePST than either young adult or nonfalling elderly individuals. i%I3 tudy alsoshowed that there was no dtfeyence in balance strategy scores between the youngadults and the healthy elderly subjects. W efore , t appears that poorp e r j i i n c e on the PST cannot be anributed to age alone, but may be predictiveof pathological processes that predkpase an individual to i q w t falls. [ChandlerJM Duncan P K St-i SA. Balance per fomme on the postural stress test:comparison of young adul&, haltby elderly, and fallen Pbys 7ber 1990;70:410-415.]Key Words Equilibrium;Geriatl ltl la;ests and measurements, functional.

The postural adjustments underlying of support. Assessment of these com-good standing balance are the result ponen ts of standing balance is a basicof integration of afferent input-pro- pa n of the evaluation of instabilityprioceptive, vestibular, a nd visual- and falling in a variety of patients.into effective mo tor responses that Many quantitative methods for testingminimize body sway and maintain the standing balance have been devel-body s cen ter of mass within its base ope d. The major qu antitative methods

J Chandler, MS, PT, is Clinical Associate, Graduate Program in Physical Therapy, Duke University,PO Box 3965 Durham, KC 27710 (USA). Address all corresp onde nce to Ms Chandler.P Duncan, MA, F T, is Associate Professor, Graduate Program in Physical Therapy, Duke Ilniversity.S Studenski, MD, is Assistant Professor, Department of Medicine, Duke University, and Chief, Reha.bilitation Medicine Service, Veteran s Administration Hospital, Durham, UC 27705.This research was conducted in the Department of Physical Therapy at Duke University and in thePostural Control Laboratory at the D urham Veteran s Administration Hospital and was supp ortedwith Funding from the Charles Dana Foundation Inc.This study was app roved by the Duk e University Institutional Review Board.bb articleul s submittedJanzuuy 18 1983 nd ul s accepted March 12 1990.

Julie M ChandlerPamela W DuncanStephanie Studenski

that have evolved includ e 1 timedbalance tests, ,2 2 meas ures of staticand dynamic postural sway that useforce platforms or other instrumentsto measure body sway?.4 and 3) bal-ance tests that challenge the subject spostural control system by perturbingthe base of su ppo rt and that analyzethe subject s moto r resp onses by inte-grate d electromyography.5,6 The costand complexity of some of these testsmake them impractical for clinicalapplication.On e safe, semi-quantitative, and inex-pensive measure of balance perfor-mance introduced by Wolfson andcolleagues7 is the postural stress test(PST). In this test, motor responses topostural pe rturbations of varying

Physical Therap yNolum e 70, Num ber 7/July 1990 410111

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Fig 1 Scoring of the postural shes test. Ratings are based on the adaptit~eness balance strategies used subjects followingeach po.~teriorperturbation I , 3 , nd 4 of body weighlj. Reponses are ranked in qualitatiz~ely ecreasing order of adaptive-nes Balance strate@,scores of 2 through 0 indicate ineffective balance responses tbat u~ould mit in a fall. (Reprinted with permis-sion @om the Ammencan eriabia SocieQ and WolfsonLI WhippleR Amaman P et al. Shesing the postural response: a quantitativemethod for testing balance.J m Geriatr Soc. 1786;34:845-850.7)degrees are measured during normalstanding by using a sim ple pulley-weight system that displaces the centerof gravity behnd the base of suppon.7Specifically, the PST m easures a n indi-vidual s ability to w ithstand a ser ies ofdestabilizing forces applied at the levelof the subject s waist. Scoring of th epostural responses is based on a nine-point ordinal scale (Fig. I , where ascore of 9 represents the m ost e5cie ntpostural response and a score of 0represents a com plete failure toremain upright.Wolfson et al7 have used the PST pri-marily with eld erly individuals andhave determ ined 1 that elderlynursing-home residents who fall scoresignif cantly lower than elderly, non -falling nursing-home residents oryoung controls and 2) that elderly,nonfalling nursing-home residentsscore significantly lower than young

controls. They conclude that the PSTcan be used to effectively predictthose at high risk for falling. Further-more, because older subjects tendedto have lower balance scores, Wolfsonet a1 suggest that the PST can be usedlongitudinally to follow balanceresponses in an individual and thatthe PST can b e used as a tool for fur-ther clarifying the nature of balanceresponses. Once individuals are iden-tified to be at risk for falling, they maybe aided by conditioning of balanceresponses or other interventions tocounteract balance deficits. Theauthors sample of nonfalling elderlyindividuals, however, consisted pri-marily of nursing-ho me residents, agroup not representative of thehealthy, community-dwelling, elderlypopulation. It remains unclear, there-fore, whether truly age-related differ-ences in balance performance aremeasured by the PST.

Age-related changes in postural con-trol are well docum ented in the litera-ture. W oollacott and colleagues6 citeevidence for changes a t all levels ofthe postural control hierarchy in theaging motor system. Such changesappear to be greatest at the higherlevel of vestibular control, moderateat the level of automatic posturalresponses, and minimal at the m ono-synaptic level. Specifically, the autho rsrepo rt results of their own workshowing that automatic posturalresponses we re delayed and that synergistic organization of posturalresponses was altered in a gro up ofelderly individuals (aged 61-75 years)who underwent sudden movement ofthe su pport surface. Furthermore,Overstall et a18 have reported thatsway while standing on a nonmovingsurface (static sway) increases withage, especially in wom en. In a gr oupof individuals aged 75 to 84 years,

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Rrocklehurst et a19 found that staticsway was a lso significantly increase din individuals wh o expe riencedchronic falls.Although such measures of static anddynamic postural co ntrol ar e sensitiveto the effects of age, they requireexpensive equipment and ar e there-fore not widely available for clinicaluse. The PST differs from these mea-sures in that it is an inexpensive testthat can he easily administered in aclinical setting. Wolfson et a17 demon-strated that the PST is sensitive tochanges in postural contro l in bothelderly nursing-home nonfallers andin elderly nursing-hom e fallers. Itremains unclear, however, whetherthe PST is sensitive to alterations inpostural control in healthy,community-dwelling, elderlyindividuals.The purpose of this study was to com-pare performance on the PST amongthree group s: 1 ) healthy young adults;2) healthy, comm unity-dwe lling, non-falling, elderly individuals; and3) elderly individuals with a history offrequent falls. The research que stion ofinterest was whether age-relatedchanges in balance performance ar emeasureti by the PST. We hypothe-sized that there w ould b e n o differ-ence in balance performance betweenthe young adults and the healthyelderly subjects, but that there wouldbe a significant ddference in balanceperformance between the elderlyfallers and both young and elderlynonfallers.MethodSubjectsOne hundred eighteen male andfemale volunteers participated in thisstudy. The subjects we re divided intothree groups: 1) healthy young adultcontrols; 2) healthy, community-dwelling, nonfalling, elderly individu-als; and 3) elderly fallers (Table 1). Afaller was defined as an individual

able 1 Subject Groups IdentiJied Age and Gender

GroupAge ~ r ) GenderX s Range M F

Young adult controls 30.6 6.3 2 w o ) 14 28Healthy elderly nonfallers 70.7 7.4 661 2) 29 37Elderly fallers 78.2 8.0 6695) 7 3

who has had two or more un-explained falls within the 6-monthperiod prior to the study in theabsence of syncope, acute illness, oran unusual environmental event oractivity. A fall was defined as any dis-turbance of balance that results in afailure to maintain upright po stureduring routine activities.All h ealthy, community-dw elling,elderly volunteers were screened fora history of lower-quarter orthope dicproblem s, neurologic disease, dizzi-ness, a nd visual deficits. Any v olun -teers wh o had a history of majororthopedic (eg, hip replacement,fused joint, o r amputation), visual,neurologic, vestibular, or othe r bal-ance disorder were excluded fromthe study.Informed consent was obtained fromeach individual prior to participationin the study. Subjects we re recruitedfrom the following sources: DukeUniversity Medical Center (Durham,NC), the Durham Veteran's Adminis-tration Medical Center, Duke Univer-sity medical and graduate sch ools,and the Duke University Aging Cen-ter's registry of healthy, community-dwelling, elderly individuals.

Fig 2 Subject positioning for thepostural stress test. Subject stands withnormal posture as weights are droppedalong pullq track providing a destabi-lizing orce posteriorly.the waist level of each subject. Thesubjects faced away from the pulleysystem and stood with their arms attheir sides, their eyes o pen , and theirfeet in a normal, comfortable stance(Fig. 2). A weight belt was fastenedaro und each subject's waist, and thepulley system was then attached tothe belt at the subject's back. Each ofthree specified weights (ll h% , 3% ,and 4V % of body weigh t, with a max-imum weight of 1 0 Ib*) was used toproduce a destabilizing force.

rocedureEach subject underwent the posturalstress test as described by Wolfson etal.7 We desig ned a pulley-w eight sys-tem an d followed their testing proce-du re t o deliver a destabilizing force at

For eac h trial, o ne investigator stoodbehind the subject, supported theweight, and then dropped it approxi-

1 Ib = 0 4536 kg.Physical Ther apyN olum e 70, Number 7/July 1990



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mately 2 f t t along the pulley track,creating a posterior force at the su b-ject's waist. seco nd investigatorguarded the subject to ensure that heor sh e would not fall. third investi-gator stood about 12 ft from the sub-ject and videotaped the subject's per-formance on the PST. No visible cueswe re given to the subject by any ofthe investigators to indicate when theweights wer e about to be dro ppe d.Prior to the start of th e test, the sub-jects were informed that their balancewould be disturbed and that theirgoal was to maintain their balance inwhatever way was necessary duringthe test. No practice trials were per-formed. All subjects wer e g uardedwith similar care, regardless ofwhether they were fallers o r nonfall-ers. Weights were drop ped consis-tently in order of increasing magni-tude; the subjects, howe ver, we re notinformed about either the relativemagnitude of the perturbing force orthe exact moment that the perturba-tion would occur. Each subject pe r-form ed a total of t hre e trials.ScoringBalance strategy scores Themotor response s that the subject usedto recover balance after each pertur-bation were videotaped. An RCA high-quality cam era-record er* was locatedapproximately 12 ft from the subjectand abo ut 45 degrees to the right ofthe frontal plane. Two of the th reeinvestigators independently viewedthe videotape in ord er to score thesubject's balance responses.Scoring was based on the nine-pointscale d escribed by Wolfson e t a17(Fig. 1). balance strategy sco re(HSS) of 9 represe nts th e most ef i-cient level of response in which onlyminor postural adjustments are usedto recover balance. Balance strategyscores of 8 and 7 indicate that addi-tional ankle, sho ulde r, o r trunkmotion is neede d to maintain balance.

* ~ o d e lPR 250 RCA Corp, Consumer Electronicsolis. IN 46206.

BSS of 6 or 5 is assigned if the s ub -ject takes o ne o r two steps (balancestrategy 6) or m ore than two steps(balance strategy 5) backward in addi-tion to flexing the trunk and shoulde rto recover balance. BSS of 4 or 3 isassigned when a subject shows noevidence of trunk and sho ulder syner-gies and compensates for posteriordisplacement solely by taking on e o rtwo steps (balance strategy 4) ormo re than two steps (balance strategy3) backw ard. BSS of 2 is assignedwhen the subject shows inadequateshoulder and trunk synergies andstepping reactions to recover balance.BSS of 1 is assigned when the sub-ject show s no synergies or stepp ingreactions but demonstrates a protec-tive landing response in anticipationof a fall. BSS of 0 is assig ned whenno corrective or protective landingresponses ar e demonstrated.Each of three trials was scored foreach subject. The total s core for thethree trials was calculated andreferred to as the total BSS.7 maxi-mum total BSS of 27 (9 3 trials)was possible. All subjects testedN 118) wer e videotaped duringeach of the three PST trials. sam ple

(n 88) of those tested was used todetermine the interobserver agree-ment rate. Two observers indepen-dently viewed the videotapes andscored each trial. The nu mb er of trialsin which th ere was total agreem entbetween the observers was divided bythe total number of trials (3 88)and m ultiplied by 100. The inter-observer agreem ent rate was 89.2 .Being satisfied that our interobserveragreement for PST scoring was sufi-ciently high, we proceed ed to analyzethe PST data for the th ree g roup s ofsubjects. In cases of disagreement, theBSS assigned by the third examinerwas used.The investigators who s cored balanceresponses from the videotapes mayhave bee n aware of th e falling status

Div, 600 N Sherman Dr, P Box 1976 Indianap-

Physical

of the subject. Because scoring wasbased on th e presence or absence ofspecific balance respon ses, however,they believed that their scoring wasnot influenced by knowledge aboutthe subject.Number of trials with effectivebalance In addition to the total BSS,the num ber of trials with effectivebalance was recorded for each sub -ject. E ectiw balance was defined asthe subject's ability to maintainupright posture without interventionof another pers on o r object. trialwith effective balance, therefore, wasassociated with a BSS of 3 or aboveo n the rating scale (Fig. 1). maxi-mum of three trials with effective bal-ance was obtainable.Data AnalysisThe total BSS for each subject wascalculated by summing the BSSsacross the three individual trials.Because of the ordinal nature of thesedata, the Kruskal-Wallis rank -ord ernonparametric statistical test was usedto a ssess differences in the total BSSsamon g the three groups of subjects.Further pair-wise comparisonsbetween groups were then madeusing Ryan's test for ordered data.The percentage of subjects in eachgro up maintaining effective balanceon each trial was calculated. com-parison of the n um be r of effectivebalance trials among the three groupsis presen ted graphically in F igure 3.To con trol for a p otential age effecton total BSS betwee n the healthyelderly subjects (me an age 70.7years) and the elderly fallers (meanage 78.2 years), we reanalyzed thedata, eliminating th e data o n allhealthy elderly subjects aged 60 to 69years from the analysis. The mediantotal BSS of the remaining healthyelderly subjects (n 37, mean age75.5 years) was 21, the same as that ofthe entire group of healthy elderlysubjects, thereby yielding the samestatistically significant result o n theKruskal-Wallis test. Subsequent discus-sion will therefore refer to resultsobtained on th e entire group of

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healthy, commun ity-dwelling, elderlysubiects.

There was a significant difference inthe ranks of the BSSs across the thre egroups (H = 21.94, df = 2, p < .01).ost hoc analysis (Ryan's test forordered data) demonstrated a signifi-cant difference in the ranks of theBSSs between the young adult con-trols and the fallers and between thehealthy elderly subjects and the fall-ers, but not between the healthyelderly subjects and the you ng adultcontrols (Table 2).All 118 subjects demonstrated effec-tive balance o n trial 1 the mildestperturbation (I%% of body weight).On trial (3% of bo dy weight), allyoung adult controls and healthyelderly subjects maintained effectivebalance, whe reas only 60% of the fall-ers were able to d o so. On the thirdand most forceful perturbation (4%%of body we ight), all of the youngadult controls an d all but on e of thehealthy elderly subjects we re able tomaintain effective balan ce. By contrast,only 50% of the fallers were able tomaintain effective balance (Fig. 3).

Ou r findings suggest that healthy,comm unity-dwelling, elderly individu-als demonstrate balance strategiessimilar to those of young adults asmea sured by th e PST. Elderly fallers,however, show ed significantly lesseffective balance strategies and w eretherefore more likely to fail portionsof the test, especially as the b ackward-perturbation force increased.The balance strategies demonstratedby the healthy elderly subjects and theyoung adult controls follow the samepattern described by Wolfson et al.'In both studies, for exam ple, elderlysubjects and young adults primarilyused an an kle dorsiflexion strategy atthe lowest perturbation in ord er toeffectively recover balance. A BSS of 9was common in both groups. Withincreasing perturbations, both g roupstended to use wellcontrolled one- to

Fig.3. Companion of the number of effective balance trials among the threegroups. Fipr e shows the percentage ofsu&ects in each group scoring3 or higher (effec-tive balance) on each of the three postural stress test trials. At least 98 of all su&ectsin the young adult and healtby elderly groups scored 3 or higher on all three trialswhereas only 50 of the fallers were able to do so. Forty percent of the fallers had onlyone trial with effective balance.

Fallers Healthy Elderly Young Adultsn=10) n = 6 6 ) n = 4 2 )100-

three-step strategies, along with the This latter finding is in contrast t o thatsho uld er and trunk synergies, to of Wolfson et a1,7 wh o found thatrealign th eir cen ter of gravity over elderly nonfalling nu rsing-home resi-their base of suppo rt. Balance strategy dents used less sho uld er and trunkscores of 6 or 5 were comm on for flexion during th e m or e forceful per-

of

both groups. turbations an d the refore receivedlower BSSs than the younger controls.They further suggest that the loss of

:.:.:.::::::~iiiii:.:.:......

Table 2. Comparison of Balance Strategy Scores (BSSs) Among the Three Su&ectGroups

......g.;::::::, $.....

Total SS

50- :::::::Group :::::::::::::

Young Adults Healthy Elderly Fallersn = 42 n = 66 n = 10)Median BSS 21 2 12Median rank 65 65 4.5

i i i 1 1 1 1 1 1 1 10 1 2 3 0 1 2 3Num ber of Tr ia ls with Effective alance

mii::::::::::::....:::::::.............iiiiiii

rn

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shoulder and trunk flexion synergiesin older nonfalling individuals repre-sents a mild deterioration in posturalresponse that may be associated withage alone. Because our study did notshow a significant difference betweenBSSs on the PST in the young adultsand the healthy elderly subjects, wehypothesize that the posturalresponses to backward perturbations,as me awre d by the PST, d o not nec-essarily deteriorate w ith age. Wolfsonand colleague^'^ observation is morelikely related to the fact their theirsam ple of nonfalling nursing-hom eresidents is not representative of thehealthy, community-dwelling, elderlypopulation.O ur finding that elderly fallersshow ed significantly less effective bal-ance strategies on the PST than eith ernonfalling elderly subject5 or youngadult controls is similar to thatreported by Wolfson et al.' At thelowest perturbation, RSSs rangedfrom 7 to 3, indicating that subtle ,covert postural adjustments (asdesc ribed by a BSS of 9) we re no tsufficient to recover balance. At themo re forceful perturbations, fallerstypically took multiple small stepsbackward, with o r without associatedtrunk and shoulder synergies, butoften failed to recover their balancewithout intervention from one of theexaminers.Although there were gender differ-ences between our g rou p of healthy,

community-dwelling, elderly subjects(56 women) and our group ofelderly fallers (30 wom en), we donot believe that ge nder account? forthe differences in RSSs on the PSTbetween th e two groups. Insubstantialevidence exists in the literature tosuggest that gender significantly influ-ences age-related changes in posturalcontrol. Overstall et aln found thatstatic sway increased w ith ag e, espe-cially in women. In a more recentstudy, Rrocklehurst et a19 found thatsway wa5 influenced by age on ly, notby gender. To da te, no oth er investi-gator has shown that there are signifi-cant differences between men a ndwomen in postural control mea5ures.Overstall and a5sociates'n finding thatwomen may show increased swayshould not be overlooked. However,the fact that our sample of fallers con-sisted primarily of men an d ou r sam -ple of healthy, nonfalling, elderly sub-jects consisted primarily of womenstrengthens our argument that gende rdid not contribute significantly to o urfindings.SummaryBased on data from ou r large sampleof healthy, community-dwelling, non-falling, elderly individuals, it appea rsthat the PST may not be sensitiveenough to detect subtle age-relateddeteriorations in postural control. Inaddition, the fact that ou r sam ple ofelderly fallers was limited to only 1 0subjects may restrict the strength of

ou r conclusions. Yet, the relativelyhigh incidence of ineffective balancerespo nses (BSSs of 2 or less), coupledwith relatively low RSSs on th e PST inthe elderly fallers as compared withthe healthy elderly subjects and theyoung adult controls, suggest5 that thePST may be a sensitive, easily adminis-tered clinical tool for identifying andmonitoring individuals who have seri-ou s balance deficits. Further testing ofthe PST in a larger sample of elderlyfallers is w arranted.eferencesPotvin AR Syndulko K, Tourtellotte WW, e tal. Human neurological function and the agingprocess. J Am GerianSoc. 1980;28:1-9.Bo han non RW, Larkin PA, Cook AC, et al.

Decrease in timed balance test scores withaging. P@s 7bm. 1984;64:1067-1070.3 Fern ie GR, Gryfe CI, Halliday PJ, et a ]. Th erelationship of postural sway in standing to theincidence of falls in geriatric subjects. Age Ageing 1982;l : l l -16.4 Shimba T. An estimation of c ent er of gravityfrom force platform data.J Biomech.1984;17:5>60.5 Nashner LM. Fixed patterns of rapid postureresponses amon g leg ~nusc les uring stancex p Brairz K e s 1977;30:1>24.

6 Woollacott MH, Shumway -Cook A, NashnerI.M. Postural reflex es an d aging. In: Mortime rJ, Pirozzolo F, Malletta G , eds. 7be Aging Ner11ou850.8 Overstall PW, Exton-Smith AN, Imms FJ, etal. Falls in the elderly related to posturalimbalance. Br Med J 1977;1:261-264.9 Brocklehurst JC, Robenso n D, James-GroomP: Clinical correlates of sway in old age: sen-sory modalities. Age Ageing. 1982 ;ll :I-10.

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1990; 70:410-415.PHYS THER.StudenskiJulie M Chandler, Pamela W Duncan and Stephanie AFallersComparison of Young Adults, Healthy Elderly, andBalance Performance on the Postural Stress Test:

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