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1998; 78:577-592.PHYS THER.Fiona Smithson, Meg E Morris and Robert IansekParkinson's DiseasePerformance on Clinical Tests of Balance in

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Performance on Clinical Tests ofBalance in Parkinson s Disease

Background an d Purpose. Due to the high incidence of falls in people withidiopathic Parkinson s disease (PD ), he assessment of standing balance isa key component of physical therapist evaluation. This study investigatedperformance on clinical tests of standing balance in subjects with andwithout PD. Subjects. The subjects were 10 persons with PD who had ahistory of falls (age range=60-80 years), 10 persons with PD who had nohistory of falls (age range=63-79 years), and 10 persons with no knownneurological impairment (age range 60 -78 years) who served as acomparison group. Methods. Subjects were tested on their ability tomaintain stability in 3 conditions: (1) steady standing (feet apart, feettogether, tandem stance, step stance, and single-limb stance), (2) inresponse to perturbations generated by self-initiated movements (armraise, functional reach, bend-reach, and step tests), and (3) in response toan external perturbation to upright stance (shoulder tug). Balance wasmeasured at peak dosage in the levodopa medication cycle (in themorning) and 7 days later. Results. The mean Hoehn and Yahr DisabilityScale score was 3.0 for the fallers with PD and 2.5 for the nonfallers withPD. Performance on the tandem stance, single-limb stance, functionalreach, and shoulder tug tests demonstrated differences between thesubjects with PD and the comparison group and between the fallers andnonfallers with PD. The results of these tests were highly repeatable over7 days (ICC=.61-.94). Conclusion and Discussion. Although there was asmall sample size, performance was highly consistent across 7 days whentesting occurred during peak dosage of levodopa. A small battery of testswere sensitive enough to discriminate between people with PD who falland those with no history of falls. [Smithson F, Morris ME, Iansek R.Performance o n clinical tests of balance in Parkinson s disease. hys Ther1998;78:577-592.1

Key Words: Balance Movem ent disorders Par kinso n s disease Postural control.Fiona SmithsonMeg E Mow isRobert Zansek

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ssessment of balance in standing is a keycomponent of the physical therapist evalua-tion for people with idiopathic Parkinson'sdisease (PD ). Due to depletion of dopamine-

producing neurons in the basal ganglia of the brain,individuals with PD experience deterioration in balanceand postural control as well as a progressive reduction inthe speed and amplitude of movements (hypokinesia)Together, these movement disorders predispose peoplewith PD to slips, trips, and fall^.^^^ Balance assessmentenables clinicians to deter mine the degree to which theyneed to address fall prevention. In this article, the termbalance refers to the ability to maintain the body's

center of mass over the base of support in order to retainstability.A large range of clinical tests have been used by physicaltherapists to assess balance in elderly people and peoplewith neurological disorders. These tests are summarizedin Table 1. Five main groups of tests can be identified:(1) tests that measure the ability to maintain steadystanding in a variety of foot positionsj-7; (2) tests thatmeasure the ability to maintain stability in standing whilecoping with perturbations to balance by self-initiatedmovements such as arm raises, lifting a foot up a nd downonto a step, or reaching forward8-ll; 3 ) tests of posturalresponses to an unexpected external perturbation suchas a push or pull12-I (4) functional tests of balanceduring activities such as walking, standing up, andturning17-zl; and 5 ) tests of the ability to integratevisual, somatosensory, proprioceptive, and vestibularinput in order to maintain stability in tand ding.^^ ^^Many of these tests correlate with frequency of falls inelderlyAlthough physical therapists routinely use the tests out-lined in Table 1 to assess balance in people with neuro-logical conditions, it remains unclear which tests aremost useful for delineating performance in people with

PD from performance in people without PD and whichtests are most useful for discriminating between peoplwith a history of falls and people with no history of fallsBecause the entire battery of tests is too extensive toadminister to any single individual, there is a need toidentify a small subgroup of tests that fulfill this need.The motor functions of the basal ganglia provide ahelpful guide to the clinical tests that are most likely tobe useful in the evaluation of people with PD. The basaganglia have 2 major roles in motor control. The firsrole is to maintain the activity of set-related neurons inthe motor cortex in a state of readiness for action. Thipreparation enables postural muscles to be recruited ina feedforward manner so that when movement occursthe person can maintain his or her center of mass ovethe base of support. The second role of the basal gangliis to provide phasic internal cues that activate submovements in long movement sequences with appropriatetiming.26The disorders of balance and postural controo b s e ~ e dn people with PD appear to be mainly relatedto defective set-related activity, which in turn disniptanticipatory postural adjustments, allowing posturamuscles to be recruited with adequate response ampli

Although the sequencing of activation in lower-limb and trunk muscles in response to unexpectedperturbations appears to remain intact, the timing omuscle activation is slower than usual and the size omovement responses is di m in i~ h ed .~ .~ ~ndividuals witPD, however, can enhance set-related activity by del iberately focusing their attention o n the task, ' therebusing frontal cortical regions of the brain to overridedefective basal ganglia circuitry.32

People with PD are likely to have difficulty responding tounexpected perturbations to their body's center of massConversely, they should be able to maintain a range osteady stance postures to the same extent as agematched individuals without PD because they presum

F Smithson, BAppSc( PT), Grad Dip (Health Research Metho ds), is Senior Physiotherapist, Geriatric Research Unit, Kingston Centre, CheltrnhamVictoria, Australia.ME Morris, PhD, MAppSc, BAppSc(PT), Grad Dip (Geronto logy), is Manager, Geriatric Research Unit, Kingston Centre, M arrigal RdCheltenham, Victoria 3192, Australia, and Senior Lecturer in Physiotherapy, La Trobe University, Bundoora, Victoria, Australia. Address acorrespondence to Dr Morris at the Kingston Centre address.R [ansek, PhD, FRACP, is Director, Movement Disorders Program, Kingston Centre.This study was conducted in partial fulfillment of the requirements for Ms Smithson s postgraduate diploma at the School ot PhysiotherapyLa Trobe Universitv.This study was approved by the Kingston Centre Ethics Committee.This study was supported by Grant No . 971268 from the National Health and Medical Research Council (NHMRC) of Australia.This article was submitted March 7, 1997, and w as accqted December 17, 1997

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ably can use attentional processes to override the defec-tive contribution from the basal ganglia. Responses ontests of self-initiated movement should not be differentfrom normal responses, provided that ( 1 ) such testsallow people with PD to focus their attention on the taskand ( 2 ) the tests do not have a timing component thatcould be influenced by the effects of parkinsonianhypokinesia. In examples such as the step test, in whichsubjects are scored on the number of times they lift theirfoot onto a step in 15 seconds, it seems likely thatperformance would be slower than usual due tohypokinesia.Previous research provides some support for these pre-dictions. Although investigators have not yet evaluatedthe ability of people with PD to maintain standingpostures, laboratory studies on anticipatory posturaladjustments confirm that people with PD usuallyrespond well to self-induced perturbations to their bal-ance, provided they have time to Experi-ments by Traub e t a136 have shown that anticipatorypostural responses induced by an unexpected externalperturbation of a hand-held lever system are reduced orabsent in people with PD.In deciding whether a particular balance test is useful forpeople with PD, therapists should have information onwhether the results can be used to discriminate betweenpeople with PD who have a history of falls and peoplewith PD who have no history of falls. There have been nosystematic attempts to document the results of clinicaltests of balance in relation to history of falls in peoplewith PD, even though this knowledge might be useful inearly detection of patients at risk of injury. Therapistsalso need to know whether performance on a test isrepeatable over time. Although interobserver and retestreliability of measurements of balance and posturalcontrol have been reported for elderly people with noknown neurological impairment and for patients withstroke,7,17,20,37,38eliability remains undocumented formeasurements from persons with PD. Clinicians needthis information so that they can make judgments aboutthe relative contributions of measurement error, patientvariability, and treatment to changes in performanceover time. Recent research on gait disorders has shownthat the footstep pattern in people with PD remainsstable, provided that they are tested at peak dosageduring the medication c y ~ l e . ~ ~ , ~ ~hether this findingapplies to performance on clinical tests of balance inpeople with PD remains open to question.

able 1Clinical Tests of Balance Used by Physical Therapists

Classification TestSteady standing Feet apart5z7

Feet t~ ge th er ~ , ~Stride stance7,l4Tandem stance7Single-limb ~ t a n c e ~ , ~Romberg Testz5,

Perturbation of standing Arm raises7balance by self-initiated Step test'O,movements Functional

Response to externally Sternal push16generated perturbations Postural stress' 2-14,0

Pastor, Marsden, and DayTest15

Ability to maintain balance Berg Balance Scale17,during functional tasks Get up and go test19,Gait20,21

Tinetti Mobility Index1',Subcomponents of functional

assessment scales such asBarthel Index, FunctionalIndependence Measure,and Webster S~ a l e ~ ~ , ~ , '

Ability to integrate sensory Sensory ~ r ~ a n i z a t i o n ~ ~ - ' ~information to maintainstability

Tests shown to correlate with the frequency of falls in elderly people (agerange=60-I04 years) .

Wade D T, Collin C. The Barthel ADL index: a standard measul-e o physicaldisability? It~lmational isability Studaes. 1988;10:64-67.'Granger CV amilton BB, Sherwin FS. Guirlej or the Use o thr C ni/om DataS e t / m Medical Rehabilitation. Buffalo, NY: Uniform Data System for MedicalRehabilitation Project Office, Buffalo General Hospital; 1986.

pected perturbations to the body's center of mass. Theresults from subjects with PD who had a history of falls,subjects with PD who had no history of falls, andage-matched comparison subjects were compared.Because physical therapists routinely reassess patients atweekly intervals, the repeatability of performance over 7days was examined to gain some insights into retestreliability of measurements obtained with the tests, cou-pled with intrasubject variability. Based on the role ofthe basal ganglia in regulating feedforward posturalcontrol, we predicted that tests of unexpected externalperturbations would best discriminate among subjectswith PD who had a history of falls, subjects with PD whohad no history of falls, and comparison subjects. We alsopredicted that subjects with PD and comparison subjectswould show similar performance on tests of steady

The main purpose of our investigation was to identify standing and ability torespond to internal perturbationclinically useful tests of balance for people with PD by the center provided that these testssystematically evaluating performance in ( I ) steady subjects to focus their attention on the task and did notstanding, (2) response to self-initiated perturbations to have an inherent requirement for the performance ofthe body's center of mass, and (3 ) response to unex- fast, repetitive movement. Finally, we predicted thatperformance would remain stable over a 7-day period

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Table 2.Characteristics of Subjects With Parkinson s Disease (PD) Who Had a History of FallsSubject Age Height Weight Webster Duration DosageNo. Y) Sex m) kg) Scalem Score of PD y) Medication mg/d)

65 F 1.54 43.0 10 9 Sinemet 100/25Sinernet CR 90 0/ 22 5Eldepryl 10Arnantadine 1002 Sinernet 50 0/1 25Sinernet CR 10 0/ 253 Sinernet 100 /25Sinernet CR 80 0/ 20 04 Madopar 200 150/37.5Sinernet CR 1,00 0/25 0Eldepryl 55 Sinernet 30 0/7 5Sinernet CR 20 0/ 50Selegiline 10Motiliurn 606 73 M 1.73 60.8 6 5 Sinernet 800 /20 07 80 M 1.60 59 .8 9 15 Sinernet 800/200

Syrnmetrel 2008 78 M 1.68 83.2 8 3 Sinemet 800 /20 0Motiliurn 409 74 M 1.67 73.4 12 13 Madopar 200 1,250/3 12.5Motiliurn 60Sinernet CR 40 0/ 10 0

10 66 F 1.56 57.0 10 13 Madopar 200 750/187.5

when subjects with PD were tested at the peak dosageduring the medication cvcle.

Methodubjectstotal of 30 elderly subjects were rec ruited for the study.

Ten subjects with idiopathic PD a nd a history of falls an d10 subjects with idiopathic PD without a history of fallswere recruited from the Kingston Centre MovementDisorders Clinic (Che lten ham, Victoria, Australia). Tenage-matched subjects were recrui ted from the VolunteerSenices Unit of Kingston Centre to serve as a compari-son group . Tables 2 through 4 provide a summary of thecharacteristics of the subjects. A f ll was defined as adisturban ce to the body's center of mass that resulted inthe person involuntarily coming to the ground. f llerwas defined as a person who had exper ienced 2 or morefalls in the 12-month period immediately prior to thestudy. history of falls was obtained by a self-report fromeach subject with PD and was verified by an interviewwith his or he r caregiver.To be included in this study, subjects were requ ired to bebetween 50 and 85 years of age , medically stab le, able towalk a 1 4 m distance at least times without assistive

devices or assistance from a not he r person, a nd able toprovide informed consent a ccording to the Declarationof Helsinki (1964). Subjects were excluded if they hadneurological conditions other than idiopathic PD adetermined by a neurologist, scored greater than 3 onthe H oe hn an d Yahr Disability Scale, ' scored less than20 on the Shor t Test of Mental Status,4%r were takingtranquilizers. Subjects were excluded if they gcoredhigher tha n 20 on the Webster Scale, which measurefunctiona l disability in relation to gait, tremor, balancerigidity, hypokinesia, seborrhea, facial expression, andspeech. Subjects were not included if they exhibitedpostural hypotension, visual disturbance, or vestibuladysfunction affecting balance, as screened by a neurologist (R I); cardiovascular disorder s affecting locomotion; or musculoskeletal disorder s, including lower-limfractures or osteoarthritis, limiting loconlotion or balance. Subjects with severe lower-limb dyskinesia, adete rmined by a neurologist ( RI), were not included.All subjects with PD were tested in the mornings durinthe on phase of the medication cycle, which \\.as at leas60 minutes after ingesting medication a nd when thewere moving freely and easily without dystonia , excessivrigidity, or tremor. Subjects with PD with a history of fallwere tested a n average of 87 minutes after their medica

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able3.Characteristics of Subiects With Parkinson s Disease (PD) Who Did Not Have a History of FallsSubject Age Height Weight Webster Duration DosageNo. Y) Sex m) kg) Scale4j Score of PD y) Medication mg/d)

72 F 1.64 62.8 4 2 Sinernet 600/ 502 63 M 1.79 89.8 5 10 Sinernet CR 1,100/275

Sinernet 50/12.5Disipal 100

3 70 1.54 71.4 3 4 Modopar 200 600/ 1504 79 1.60 60.0 6 2 Kinson 200 1,500/3755 64 F 1.54 60.8 13 17 Modopar HBS 500/ 125

Sinernet 100 50/25Motiliurn 10Cogentin 0.56 78 M 1.73 79.6 3 4 Madopor 800/200

Motiliurn 407 76 M 1.64 70.4 6 9 Sinernet 800/200Modopar HBS 400/ 00

Pergolide 28 65 M 1.74 95.4 6 Madopar Q 400/ 00Modopar HBS 200/50

Eldepryl 109 70 M 1.71 67.0 5 Modopar 200 600/ 50

Madopar HBS 200/5010 7 1.62 60.4 13 15 Sinernet 100 450/12.5Motiliurn 30

Cogentin 3

able 4.Characteristics of Elderly Subjects With No Known NeurologicalImpairment [Comparison Group)

Subject Age Height WeightNo. Y) Sex m) kg1

73 M 1.79 86.02 66 M 1.59 67.63 78 M 1.69 65.84 75 M 1.73 92.85 68 F 1.56 67.26 76 F 1.46 47.47 60 1.56 64.28 78 M 1.75 76.69 67 1.60 72.810 65 1.57 74.4

tion and subjects with PD without a history of falls weretested an average of 103 minutes after their medication.The types and dosages of PD medications are summa-rized in 'Tables 2 and 3.In the sample, the mean age was 70.6 years (SD=6.4,range=60-80) for subjects with PD who had a history offalls, 70.8 years (SD=5.7, range=63-79) for subjects withPD who had no history of falls, and 70.6 years (SD=6.2,range=60-78) for comparison subjects. The mean dura-tion of ID was 11.6 years (SD=4.3, range=3-15) for

subjects with PD who had a history of falls an d 6.9 years(SD=5.6, range= 1-13) for subjects with PD who had nohistory of falls. The mean Webster Scale4 cores forsubjects with PD who had a history of falls were 11.1(SD=3.9, range=6-18) for test 1 and 10.1 (SD=2.9,range=6-16) for test 2. For subjects with PD who had nohistory of falls, the mean Webster Scale scores were 6.4(SD=3.7, range=3-13) for test 1 and 6.3 (SD=4.0,range=l-14) for test 2. There were no differences inWebster Scale scores from one week to the next. Themean Hoehn and Yahr Disability Scale4' scores were 3.0for the fallers with PD and 2.5 for the nonfallers with PD.issing Data

There was one missing data point in this investigation.Subject 5 of the comparison group was unable to carryout the bend-reach test during test 2 due to subacuteback pain.pparatus

Tests in steady stance were measured using a commer-cially available stopwatch (Micronta Sports ~ i m e r * ) ,which recorded time in seconds with an accuracy ofdecimal places. In order to standardize the foot place-

Tandy Electronics, 9 Kurrajong Ave, Mt Druitt, New South Wales, Australia2770.

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1 cm

rncm bParallel Stance Stride Stance Tandem Stanceigure 1.Alignment of feet for parallel stride and tandem stance positions. [Adapted from Goldie et 01.71

ment, footprint images for aligning the feet in parallel,step, and tandem stance were marked on the floor usingremovable colored contact footprint images. The ratio-nale for having subjects assume a standardized footposition was to reduce errors in measurement arisingfrom deviations from the initial stance position. Inaddition, previous researchM has shown that foot posi-tion, including the foot angle, influences standingbalance.Tests of self-generated perturbations were measuredusing the stopwatch, a tape measure, and a portable stepmeasuring 150 mm high, 290 mm wide, and 600 mmlong. Commercially available plastic pegs, which were setat 5-cm intervals along a line, were used for the bend-reach test. The response to an external perturbation wasrated by the examiner (WT) on a 5-point scale accordingto the protocol for the shoulder tug test described byPastor et al.I5

screened area within a large isolated room (2010 m) was used for all data collection. Testing in thisquiet area had the benefit of minimizing backgroundnoise, distractions, and interruptions.

ProcedurePrior to testing, the purpose of the study was explainedto the subjects, and informed consent, which outlinedthe rights of the subjects, was obtained. Height andweight were measured, and subjects were scored on theWebster Scale49 by a trained physical therapist (WT).Each of the balance tests was administered by the samephysical therapist, who was blind to the aims and designof the study. To control for series effects, half of thesubjects in each group performed the tests first in steady

standing, second in response to perturbations generatedby self-initiated movements, and finally in response to anexternal perturbation. The other half of the subjectperformed the tests in the reverse order . One week lateat the same time of day and at the same point in thelevodopa medication cycle, the procedure was repeated

alance in Steady StandingThe ability to maintain various stance positions with eyeopen and without hand support was recorded for eachsubject. The stance positions were (1) feet 10 cm apartas specified in the protocol described by Goldie et a17(2) feet together; (3) stride stance, with the subject s feeplaced 10 cm apart an d with the heel of the front foot inline with the toes of the rear foot, as described by Goldieet al7; (4) tandem stance, in which the subject stood withone foot directly in fron t of the other foot an d with thetoes of the rear foot contacting the heel of the front footand (5) single-limb stance, in which the subject stood onone foot with the opposite knee held at 45 degrees offlexion and both hips in the anatomical position.Subjects stood on the footprint templates during feeapart, stride stance, and tandem stance condition(Fig. 1) . Stride stance an d tandem stance were testedwith each of the feet in the front position. Single-limbstance duration was also recorded for both feet. The testwere concluded if subjects changed their stance position, if the examiner was required to provide externasupport, or if the subjects maintained the position fothe maximum testing period of 30 seconds. In an efforto control for the effect of fatigue and other variablesthe best of 3 scores was recorded if all scores were less

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Figure 2Position of feet and pegs for bend reach test.

oiocm

than 10 seconds. If the score exceeded 10 seconds in anytrial, that time was recorded without further trials.

o c mcminterv ls

Perturbation of Standing Balance bySelf Initiated MovementsFunctional reach test. The maximal distance each sub-ject was able to reach while maintaining a fixed base ofsupport in standing was measured following the proce-dure described by Duncan et al.g The subjects wererequired to stand with their right side close to, but nottouching, a wall and with their feet set 10 cm apart. Thesubjects were asked to raise their right arm to 90 degreeswith the hand outstretched, and the position of the thirddigit was recorded on the wall with removable adhesivetape (position 1 ). The subjects then reached as farforward as they could without moving their feet, and theposition of the third digit was recorded with anotherstrip of tape (position 2) . The difference between posi-tions 1 and 2 was then recorded using a tape measure.To minimize fatigue and the duration of testing, onlyone trial of the functional reach test was performed.Bend reach test. This new test, which has not beenvalidated previously, was included because of our obser-vations that patients with PD had difficulty retrievingobjects from the floor, apparently due to balance disor-ders. The examiner measured the maximal distance thateach subject could bend and reach to pick up an objectfrom the floor. Target objects (plastic pegs) were placedat 5-cm intervals in a straight line from the footprinttemplates described earlier (Fig. 2). The maximumdistance that the subject could successfully reach toretrieve a peg without touching down on the floor withthe hands, requiring external support from the exam-iner to steady the subject, or changing foot position wasrecorded for one trial.

Arm raise test. The arm raise test was performed asdescribed by Goldie e t al.' Subjects were required tostand with their feet placed 10 cm apart and wereinstructed to lift your arm up and down to shoulderheight as many times as you can in 15 seconds when I saygo. The tester passively moved each subject's arm up to90 degrees of flexion and down again twice in order todemonstrate the desired action. Performances for onetrial of the right and left arms were then recorded.Step test. The step test was administered following theprocedure described by Hill et a1.I0 Subjects stood withtheir feet 10 cm apart, with a 15-cm-high step positioned5 cm in front of their toes. The tester delivered thefollowing instructions: When I say go, step your footonto then off the step as many times as you can until I saystop. Make sure that all of your foot contacts the step eachtime. The number of times the subjects successfullyplaced the foot onto the step in 15 seconds was thenrecorded. This procedure was completed for both feet.Balance in Response to an ExternallyGenerated PerturbationThe external perturbation test (shoulder tug) wasadministered according to the protocol described byPastor et al.15 Subjects were positioned in steady stancewith their feet 10 cm apart. The examiner stood directlybehind each subject and delivered the instructions: Iam going to tap you off balance, and I won't let you fall.Information about the direction and timing of theperturbation was not provided. The examiner thendelivered a brief and quick tug to the subject's shouldersin a posterior direction with sufficient force to destabi-lize the subject. The destabilizing force was determinedby the examiner, who was blind to the subject's group,based on the mass of each subject.

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Postural reactions in response to the external perturba- Table 5tion were scored by the examiner using the 5-point Means and Standard Deviations for Test 1 and Test 2 Scores forSubiects With Parkinson's Disease Who Had a History ofclinical rating scale described by Pastor et all5: Falls (n=10)1. Subject stays upright without taking a step.2. Subject takes one step backward but remains steady.3. Subject takes more than one step backward but

remains steady.4. Subject takes one or more steps backward, followed

by the need to be caught.5. Subject falls backward without attempting to step.Data AnalysisIntraclass correlation coefficients (ICC[2,1]) were usedto analyze the repeatability of the measurements fromone week to the next.45 Correlation coefficients for theexternal perturbation test, which was measured on a5-point ordinal scale: were calculated using Spearman 's

Test Test 2Condition X SD X SDSteady standing s)

Feet apart 29.47 1.69 30.00 0.00Feet together 29.1 8 2.59 29.74 0.84Stride stance R] 28.31 5.34 29.02 2.68Stride stance I.) 28.17 5.78 29.43 1.80Tandem stance (R) 15.64 13.90 1 1.45 9.96Tandem stance (L) 12.27 12.63 8.22 9.52Singlelimb stance (R) 9.53 10.06 7.75 9.68Singlelimb stance (L) 9.26 10.07 8.59 9.53

Internal perturbationFunctional reach (cm) 24.45 5.93 24.10 6.41Bend-reach (cm) 64.00 8.76 65.00 9.13Arm raises (R) 11.00 2.21 12.60 2.17Arm raises (L] 10.60 1.90 12.50 1.72Step [R] 9.20 3.55 10.60 3.84Step [L) 9.70 3.53 9.80 3.80

External perturbation 3.00 1.16 3.10 1.20-Systematic trends in the data were examined byeach of the variables. Paired tests were used to deter-mine whether systematic change occurred. Variable Table 6change was estimated by obtaining the standard &via- Means and Standard Deviations for Test 1 and Test 2 Scores fortion of the change scores sD,~,) and the 95 confi- Subiects Wi th Parkinson's Disease Who Did No t Have a History ofFalls (n= 10)dence interval (CI) for individual change scores usingthe following equation:

Frequency over 15 seconds.

95 cI=D?Z,XSDdiffwhere Z,= 1.96.

calculating the mean change (D) over the 2 tests for

To determine whether differences existed among the 3groups on tests of balance over the 2 measurementsessions, 2-factor (group, test) repeated-measures analysesof variance (ANOVAs) were used.lTo control for theaccumulation of error due to multiple statistical tests,the probability values were adjusted according to theprocedure recommended by Bonferroni.16 The ScheffkF test was then used to determine whether differencesfrom test 1 to test 2 existed between fallers and nonfall-ers with PD, between fallers with PD and comparisonsubjects, and between nonfallers with PD and compari-son subjects. The external perturbat ion test was analyzedusing a Kruskal-WallisH test,47which is a nonparametricstatistical procedure used to compare 3 or more inde-pendent groups. The H test is analogous to the ANOVAused for parametric data.17ResultsRepeatability of Performance Over a 7 Day PeriodTables 5 through 7 show the means and standarddeviations for the 3 groups for the 2 testing occasions.

Test Test 2Condition X SD X SDSteady standing s]

Feet apart 30.00 0.00 30.00 0.00Feet together 30.00 0.00 30.00 0.00Stride stance [RI 30.00 0.00 30.00 0.00Stride stance (L) 30.00 0.00 30.00 0.00Tandem stance [R) 21.50 8.11 25.01 7.02Tandem stance (L) 22.12 7.76 23.04 8.85Singlelimb stance (R) 17.56 8.92 15.35 7.19Singlelimb stance (L) 14.53 8.18 15.57 8.21

Internal perturbationFunctional reach (cm) 29.95 3.82 31.95 5.64Bend-reach (cm] 65.00 3.33 64.00 3.94Arm raises (R) 13.00 2.54 13.30 2.58Arm raises (L) 12.80 2.53 13.40 2.41Step (R) 12.10 2.60 13.50 3.17Step (1) 12.20 2.86 12.50 2.55

External perturbation 2.001.41 2.101.45Frequency over 5 seconds

Tables 8 through 10 present the means and standarddeviations for the change scores from test 1 to test 2, the95 CI around the change scores, values, and correlation coefficients. On the whole, the results showedconsistency of performance over the 7-day testingperiod. Inspection of the means, standard deviationsand raw scores for the tests of feet apart, feet together

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Table 7.Means and Standard Deviations for Test 1 and Test 2 Scores forElderly Subjects With N o Known Neurologica l Impairment(Comparison Group) (n= 10)

Test TestCondition S SSteady standing (s)

Feet apart 30.00 0.00 30.00 0.00Feet together 30.00 0.00 30.00 0.00Stride stance (R) 30.00 0.00 30.00 0.00Stride a,tance (L) 30.00 0.00 30.00 0.00Tandem stance (R) 28.67 4.22 30.00 0.00Tandem stance (L) 26.53 7.33 28.74 3.98Single-limb stance (R) 20.45 10.36 22.28 10.96Single-limb stance (L) 21.27 1 1.85 21.60 10.35

Internal perturbationFunctional reach (cm) 34.20 4.12 35.05 3.60Bend-reach (cm) 66.00 8.76 67.79 7.55Arm raises (R) 13.90 3.73 14.70 2.50Arm raises (L) 13.90 3.45 14.90 2.56Step (R) 13.90 4.12 15.20 3.88Step (L) 13.50 4.22 15.30 4.45

External perturbation 1.50 0.71 1.30 0.48

and stride stance for each group and for the test oftandem stance on the right lower extremity for thecontrol group, however, indicated attenuation of thedata due to ceiling effects. That is, the majority ofthe subjects were able to maintain steady stance duringthe tests for the maximum testing period of 30 seconds.We therefore considered it inappropriate to calculatefurther correlation statistics for these particular resultsdue to the lack of variability within and betweensubjects.16Repeatability of performance in subjects with PD who hada history of falls. The results for the subjects with PDwho had a history of falls indicated strong temporalstability for repeated measurements for the tandemstance, single-limb stance, functional reach, bend-reach,step, and external perturbation tests, with ICCs rangingfrom .71 to .93. The correlation for the external per-turbation test was also strong ( r 9 9 ) . There was poorto moderate repeatability for the arm raise test(ICC=.O7-.51).For the majority of the tests, there were no differencesbetween repeated measurements from one week to thenext. The exceptions were the step test on the rightlower extremity ( = -2.585, P=.030), the right armraise test ( = -2.667, P=.026), and the left arm raisetest ( =-2 .487 , P=.035). s shown in Table 8 , thestandard deviations for the change scores were large forsome conditions, notably the bend-reach, tandemstance, stride stance, and single-limb stance tests.

Repeatability of performance in subjects with PD who hadno history of falls. The results for the subjects with PDwho had no history of falls indicated strong temporalstability for the arm raise, step, and external perturba-tion tests, with ICCs ranging from .73 to .86. Theproduct-moment correlation for the external perturba-tion test was also high r=.9 7 ) . There was moderatetemporal stability for the r ight tandem stance, right andleft single-limb stance, and right arm raise tests, withICCs ranging from .50 to .66. For the left tandem stance,functional reach , and bend-reach tests, the ICCs rangedfrom .40 to .43. Paired t tests showed no statisticallysignificant differences from on e week to the next for anyof these variables, except for the right step test( = - 2 . 4 0 9 , e . 0 3 9 ) .Repeatability of performance in comparison subjects. Theresults for the comparison subjects showed strong temporalstability for the single-limb, bend-reach, step, and right armraise tests Tab. 10) . Intraclass correlation coefficients forthese variables ranged from .77 to .89. There were moder-ate correlations between test 1 and test 2 scores for theremaining tests, with ICCs ra ng ng from .51 to .65. Thecorrelation between test 1 and test 2 for the externalperturbation test was high ( r=.96) . For the comparisongroup, there were no differences between repeated mea-surements for any of the variables.Between Group Dikrences in Test PerformanceSteady standing tests. Th e results indicated little differ-ence among groups for many of the steady standingtests. All of the comparison subjects and subjects with PDwho had no history of falls were able to maintain thesteady stance position with feet apart, with feet together,and in stride stance for the maximum testing period of30 seconds. The majority of the subjects with PD whohad a history of falls could also maintain steadystanding in these positions for periods close to themaximum testing time. In contrast, the results for thetandem stance and single limb stance tests revealeddifferences among groups. Two-factor repeated-measures NOV s showed significant main effects forright tandem stance (F=10.2; d f=2,27; P=.0005) , lefttandem stance (F=13.14; d f=2,27; P=.0001) , rightsingle-limb stance (F=4 .84; d f=2,27; P= .0 16) , and leftsingle-limb stance (F=4.61; d f=2,27; P=.02) . Theseresults were attributable to superior performance inthe comparison subjects compared with the subjectswith PD who had a history of falls, as indicated by Scheffk

tests during test 1 for right tandem stance (F=4.36;df=2,27; P


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Table 8.Means and Standard Deviations of Change Scores Dl (in Seconds), 95% Confidence Intervals (CI), t Values, and Correlation Coefficients forRepeated Measurements Taken at 1-Week lntervals for Subiects With Parkinson's Disease Who Ha d a History of Falls (n= 10)

Product-Moment ICC 2, l)Lower UPP~ Correlation Test 1

Condition D SDdiH 95 CI 95 CI Test 1 Test 2) Test 2)Steady standing (s]

. . . . . . . . .Feet apart 0.53 1.69 -2.78 3.84 . . .. . . . .eet together 0.55 2.8 1 -4.95 6.10 . . . . . . . . .Stride stance (R) 0.71 6.28 1 1.60 13.02 . . . . . . . . .Stride stance (L) 1.26 6.25 10.99 13.5 1Tandem stance (R) -4.19 7.30 18.50 10.13 1.81 .86 .76Tandem stance (L) -4.05 8.10 19.92 1 1.83 1.58 .77 .71Single-limb stance (R) 1.78 3.15 -7.95 4.40 1.78 .95 .94Single-limb stance (1) -0.67 5.5 1 1.47 10.13 0.39 .84 .85

Internal perturbationFunctional reach (cm) -0.35 2.45 -5.15 4.45 0.45 .92 .93Bend-reach [cm) 1 .OO 5.16 -9.12 11.12 -0.61 .83 .84Arm raises (R] 1.60 1.90 -2.12 5.32 -2.67' .63 .51Arm raises (L) 1.90 2.42 -2.85 6.65 -2.48' .10 .07Step (R) 1.40 1.71 -1.96 4.76 -2.59' .90 .84Step (1) 0.10 2.18 -4.18 4.38 -0.15 .83 .83

External perturbation 0.10 0.32 -0.52 0.72 .OOd .99Frequency over 15 seconds.Ellipsis denotes an indeterminate value.

i . 0 5 .M'ilco\on sign ed rank, F 3 1 7 3

'Speannan's rho.

PD who had no history of falls, even though the subjects F= 10.47; df=2,27; P< .0 5) . These results indicate thawith PD who had no history of falls consistently scored the functional reach test discriminated well among alower for these variables Fig. 3) . groups.Perturbation of standing balance by self initiatedmovements. Tables 5 through 7 show the means andstandard deviations for the self-initiated perturbationtests. The means and standard deviations for test 1 areillustrated in Figures 4 and 5. These results indicateconsiderable difference among groups for the func-tional reach and step tests, little difference amonggroups for the bend-reach test, and equivocal results forthe arm raise test.For the functional reach test, a 2-factor repeated-mea-sures ANOVA revealed a significant main effectF=12.65; df=2,27; P=.0001), with post ho Scheffk F

tests for test 1 showing differences between the subjectswith P who had a history of falls and the subjects withPD who had no history of falls F=3.4; df=2,27; P


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Table 9.Means and Standard Deviations of Change Scores D) (in Seconds), 95%Confidence Intervals (CI), t Values, and Correlation Coefficients forRepeated Measurements Taken at 1-Week Intervals for Subiects With Parkinson's Disease Who Did Not Have a History of Falls (n= 10)

Product-Moment ICC 2,l)Lower Upper Correlation Test 1Condition SDdiR 95 CI 95 CI t Test 1 Test 2) Test 2)Steady standing (s)

. . .Feet apart 0 0 0 0 . . .Feet together 0 0 0 0tride stance (R) 0 0 0 0 . . . . . . . . .tride stance (L) 0 0 0 0

Tandem stance (R) 3.51 5.77 -7.80 14.82 - 1.92 .72 .66Tandem stance (L) 0.92 9.29 -17.29 19.13 -0.31 .38 .40Single-limb stance (R) -2.21 6.67 15.28 10.86 1.05 .68 .66Single-limb stance (L) 1.04 8.35 15.33 17.41 -0.40 .48 .50

Internal perturbationFunctional reach (cm) 2.00 5.13 -8.06 12.06 - 1.23 .47 .42Bend-reach (cm) .OO 3.94 -8.73 6.73 0.80 .42 .43Arm raises (R) 0.30 2.3 1 -4.23 4.83 -0.41 .59 .61Arm raises (L) 0.60 1.65 -2.63 3.83 -1.15 .78 .77Step (R) 1.40 1.84 -2.20 5.00 -2.41' .82 .73Step (L) 0.30 1.49 -2.63 3.23 -0.64 .85 .86

External perturbation 0.10 0.74 -1.35 1.55 -0.45d 0.97"Frequency over 15 seconds." ZElPsisdenotes an indeterminate value.' P i . 0 5 ."Wilcoxon signed rank, P= 6547

Spearman's rho .

no differences in performance on the step test betweenthe subjects with PD who had no history of falls and thecomparison subjects.Response to externally induced perturbations Tables 5through 7 and Figure 6 indicate that the externalperturbation test discriminated among groups on bothtesting occasions. Kruskal-Wallis tests (corrected for ties)showed differences among groups for test 1 ( H (2 )=7.5,P=.024) and for test 2 (H (2)=9.47, P=.009).DiscussionRepeatability of Test PerformanceOur investigation represent9 the first systematic evalua-tion of performance on clinical tests of balance inpeople with idiopathic PD with and without a history offalls. Numerous findings emerged that are relevant toclinical practice. The most notable finding was that mosttests demonstrated high repeatability over a 7-dayperiod. The exceptions were the right arm raise test forthe subjects with PD with and without a history of falls,the left arm test for the comparison subjects, and the lefttandem stance, left single limb stance, bend-reach, andfunctional reach tests for the subjects with PD who hadno history of falls.

The arm raise test was the only test that demonstratedlow to moderate repeatability in all 3 groups. Potentialsources of error in clinical administration of the armraise test could have arisen from variability in theexaminer s instructions and observations, distractions inthe testing environment, and subject-related factors suchas soft tissue changes at the shoulder, adherence, atten-tion, fatigue, and alterations in levodopa status. Some ofthe subjects reported difficulty estimating and reproduc-ing the 90-degree shoulder flexion angle. Reliabilitycould have been enhanced by placing a mark on the wallindicating the criterion shoulder height or by taking themean of 3 trials of the arm raise test. Despite thesepotential sources of error, however, the mean changescores represen ted less than 2 arm raises in 15 seconds,which, in clinical terms, was a negligible change inperformance. Thus, the moderate degree of repeatabil-ity appears to be within clinically acceptable limits.Attempts were made to control for confounding factorsby using standard instructions, objective measures, reg-ular rest periods, and testing in a quiet, isolated area tominimize distraction and background noise. In addition,the medication status of subjects with PD remainedconstant over the I-week period.The strong temporal stability of performance on themajority of balance tests in this investigation is consistentwith previous research on the repeatability of gait mea-

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Table 10. aMeans an d Standard Deviations of Change Scores (D) (in Seconds), 95 Confidence Intervals (CI), f Values, and Correlation Coefficients forRepeated Measurements Taken a t1 Week Intervals for Elderly Subjects With No Known Neurological Impairment (Comparison Group) (n=10

Condit ion D S D di f fLower9 5 CI

Upper9 5 C I

Product-M o m e n tCorrelat ion(Test1 Test 2 )ICC (2,1)(Test 1-Test 2)

Steady standing (s)Feet a partFeet togethe rStride stance (R)Stride stance (L)Tandem stance (R)Tandem stance (L)Single-limb stance (R)Single-limb stance (L)

Internal perturbationFunctional reach (cm)Bend-reach (cm)Arm raises (R)Arm raises (L)Step (R)aStep (L)External perturbation

00001.342.211.840.330.850.560.801.001.301.80- 0 . 2 0

00004.225.805.655.483.424.642.102.752.543.460.79

0000- 6 . 9 3- 9 . 1 6- 9 . 2 3- 1 0 . 4 1- 5 . 8 5- 8 . 5 3- 3 . 3 2- 4 . 3 9- 3 . 6 8- 4 . 9 8- 1 . 7 5

00009.6113.5812.9111.077 559.654.926.396.288.581.35

- 1 . 2 1- 1 . 0 3- 0 . 1 9- 0 . 7 9- 0 . 3 6- 1 . 2 1- 1 . 1 5- 1 . 6 2- 1 . 6 5- 0 . 8 2 c

.62.86.89

.61.83.85.62.80

.68.96 d

.51.86.89

.62.84.77.58.77

.65Frequency over 15 seconds .Ellipsis denotes an indeterminate value.

cWilcoxon s igned rank, P=.4152 .dSpearm an ' s rho .

surements in people with PD. Morriset al3 9 repor ted a h igh degree oconsistency on tests of walking speedst r ide length , cadence, and doublelimb support duration when subjectswith PD and control subjects wereretested within a session and fromon e day to the next. Urqu hart 4 0 founthat repeatabil i ty of measurementsfor the temporal and spatial variables of gait was high over a 7-dayperiod. For both of these studies andfor our investigation, performancewas measured a t the peak dosageduring the medication cycle. In arecent study by Morris et al , 39 whensubjects with PD were tested half anhour before the next dose of levodo pa was du e (when they were ofFmedicat ion) , gai t per formance wasmuch more var iable and the s tandard er ror of measurement washigh. Fur ther research is needed tode te rmine whe the r pe r fo rmance onbalance tests shows similar variabilityacc ordin g to levodop a status. In viewof the f indings on the temporal stability of gait in persons with PD, 3 9we

Figure 3.Test 1 means and standard deviations for the steady stance conditions for all 3 groups.(PD=Parkinson's disease, FA=feet apart, FT=feet together, R SS=right stride stance,RTS=righttandem stance,R SLS=right single-limb stance.)
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Figure4.Test 1 means and standard deviations for the functional reach andbend-reach tests for all 3 groups. (PD=Parkinson's disease,FR=functional reach, BR=bend-reach.)

Figure5.Test meansandstandard d eviationsfor thestepand armraise testsforal l3 groups. (PD=Parkinson's disease,R AR=r ighta rm ra ise ,L AR=leftarm raise, R ST=right step test,LST =left step test.)

would predict that within-subject and between-subjectvariability in balance would be increased in the30-minute per iod pr iorto thenext doseoflevodopa.Wealso believe that research is n e e d e d to investigate therepeatabil i ty of per fo rmance on balance tests amongpeople wi th PD over longer per iods of time, such as1 m o n t h , 6m o n t h s , and 1year. Parkin son 's disease is achronic , progressive cond i t ion,and itwouldbe expectedthat people with PDwould show deter iorat ion in performance over these longer t ime per iods, leading to lowerintersession correlations and larger change scores.

Figure6.Test 1 meansandstandard deviationsfor the external perturbation tefor all 3 groups. (PD=Parkinson's disease, EP=external perturbation

As with previous investigations on temporal stabil i ty oper fo rmance in persons wi th PD4 0 and s t roke ,7 4 8 CIwere quite wide for the change scores over 7 days fosome of thevariables.ThewideCIsmaybe rela tedto thesmal l numbers of subjects in the 3 groups and toindividual variationsin per formanc e over t ime, a l thougerror from the tester and ins t rumen t may have contribu ted .Th eu p p e r and lower limits for9 5 %CIs of changscores provide clinicians with metric estimates of thea m o u n t ofchan ge that they nee d to observe to concludtha t differences inindividual per forman ce arelikelydueto physical therapy ra ther than measurement er rorTab le 8, for example, shows that a subject with PDwita history of falls would need to improvebymore than 3.seconds overa 1-weekper iod on the steady standin g teswith feet apart to show change exceeding that due tomeasurement er ror . S imi lar ly , a subject with PDwithhistory of falls would have to decrease his or her scorebymore tha t 2.8seconds overa 1-weekper iod to show trudeter iorat ion. Hi l l et al4 8 suggested that , in addi t ion toensur ing that all possible strategies are used to reducer ror a t t r ibutable to the measuremen t dev ice or totester- andsubject-related factors,the useof less rig orouCIs may bewar r an ted in clinical studies such asthis.Wd id not a d o p t the strategy of using less r igorous CIbecause ou r sample size was relatively small and theprobabili ty of incur r ing a Type I error would havincreased to wha t we would consider an unacceptablhigh level. Neve rtheless, theissueof clinically acceptablCIs needs to be given more considerat ion by physicatherapists and researchers in the future.
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I11 addition to the wide CIS for some variables, trendstoward practice effects were present for some tests, asindicated by the positive change scores shown in Tables8 through 10. These systematic improvements have beenfound for similar tasks in another investigation7 and canbe expected for unpracticed novel tasks. Despite thesetrends, the CIS provide the clinician with estimates ofthese practice effects, which is helpful in determin ingwhether a change is associated with physical therapy.Differences in Performanc e Amo ng GroupsSimilar to the comparison subjects, the subjects with PDhad no difficulty maintaining steady standing with theirarms by their side and their feet apart, together, or in thestride stance position. Most subjects could maintainthese postures for the maximum testing time of 3seconds. In contrast, there was considerable differencein performance benveen the subjects with PD and thecomparison subjects on tests that perturbed balance byself-initiated movements. Th e functional reach and steptests differentiated not only between the subjects withPD and the comparison subjects but also between thesubjects with PD with an d without a history of falls.Performance on the external perturbation test alsoshowed clear differences among the 3 groups.Tests of steady standing in the feet apart, feet together ,and stride stance positions showed a lack of sensitivitydue to ceiling effects. This result was consistent withprevious findings for patients with stroke and elderlysubjects with a history of fall^.^,^.^. Because these testsfail to discriminate between people with and without PDor between people with PD with and without a history offalls, they appear to be of limited use in the physicaltherapy assessment of people with PD. Increasing thetest duration from 3 seconds to 60 or 90 seconds mightenhance the discriminative properties of these tests. Ourobservations together with consideration of the move-ment disorder literature, however, suggest that this is notthe case. In steady standing positions where there a re nocompeting attentional demands, people with PD appearto be able to override the defective basal ganglia input tothe maintenance of postural set by consciously attendingto maintainingAn unexpected finding was that performance on tandemstance and single-limb stance tests yielded marked dif-ferences between the subjects with PD who had a historyof falls and the comparison subjects, although there wasno difference between the subjects with PD who had nohistory of falls and the comparison subjects. Our predic-tion was that all 3 groups would show similar ability onthese tests. The finding that the subjects with PD whohad a history of falls could maintain these positions onlyfor approximately two thirds of the time achieved by thecomparison subjects when there were no competing

attentional demands raises the possibility that a centradeficit in postural control exists in people with PD thamay be only partially compensated for by cognitivprocesses. The differential findings also suggest thatandem stance and single-limb stance are useful tests inallowing physical therapists to screen for balance disoders that may place people at increased risk of falling.The results for the functional reach test showed diffeences among the 3 groups. Previous studies on elderlpeopleHand patients with stroke4Y re in agreem ent witthis finding and suggest that the functional reach test is useful clinical tool in assessing balance in peoplwith neurological disorders an d in detecting differencebetween people with and without a history of falls. Icontrast, the bend-reach test showed poor discrimination among groups and does not appear to be a usefuclinical tool for assessing balance in people with PD. Thdifference in discriminative properties between theseself-initiated tests could arise from the inherent naturof the tasks. The bend-reach test provides a klsual cuthat the subject can use to guide performance, whereathe functional reach test has no visual target and appearto require internal guided movement control, which iimpaired in people with PD. Performance on both othese tests is also dependent on the person's height andthe flexibility of the musculoskeletal system, althoughthe requiremen t for flexibility is probably accentuated ithe bend-reach test.Although the step and left arm raise tests discriminatedwell among groups, clinicians should be cautious wheninterpreting findings from these tests because of thpotential for hypokinesia and akinesia to confoundscores. People with hypokinesia experience slowness inperforming repetitive sequential movements, whereapeople with akinesia take longer than usual to initiatmovement sequences. Whether differences amongroups on the step and arm raise tests were due topostural instability, hypokinesia, akinesia, or a combination of these movement disorders remains unclear. Onconsideration is that step test scores for the subjects withPD who had a history of falls in our investigation werslightly higher than previous results for elderly peoplewho had no history of PD yet had a history of stroke anfalls.1 This finding argues against the predominaninvolvement of hypokinesia in the step test results.The external perturbation test yielded marked differences in performance. On clinical observation, it wasapparent tha t the majority of subjects with PD who hada history of falls failed to display effective steppingstrategies because their response was underscaled in sizor excessively slow. Six of these subjects needed to bcaught by the examiner after the perturbation. Thsubjects with PD who had no history of falls showed

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slower stepping responses yet were able to regain stabil-ity after taking one or more steps backward. The com-parison subjects were able to maintain their balance byeffectively using a stepping strategy.

linical ImplicationsTh e results of our study provide clinicians with a batteryof tests that appear to be sensitive enough to discrimi-nate between people with PD who have a history of fallsand people with PD who have no history of falls. The testbattery also appears to be useful in discriminatingbetween people with PD and people with no knownneurological impairment. This information might assistphysical therapists in predicting which people with PDare at risk of falls. Due to the simplicity and applicabilityof the tests within the clinical setting, minimal training isrequired for the physical therapist to administer thetests. Furthermore, the tests are highly portable, rela-tively quick, require very little equipment, and arecost-effec: ive.

The results showed strong repeatability of the test bat-tery over a 7-day period, which is encouraging forclinicians who commonly examine patients weekly ormore frequently. Weekly screening assessments of bal-ance may be valuable in de tecting any decline in balanceand could provide a signal for required intervention.Similarly, improvements may be noted with physicaltherapy input. The tests that demonstrated the bestdiscrimination and repeatability were the tandem stanceand single-limb stance test, the functional reach test, andthe external perturbation test.A number of limitations of ou r study need to be acknowl-edged. The relatively small number of subjects in eachgroup may have influenced the probability of samplingerror as well as the risk of increasing Type I1 errors.46 naddition, the exclusion of subjects with PD who hadsevere dyskinesia limits the generalizability of findings topeople without that movement disorder. We did notevaluate performance on the sensory organization testbecause vestibular, proprioceptive, and visual functionsremain intact in people with PD.3 We also did notevaluate performance on what are often consideredfunctional tests of balance such as the timed up and gotestlg or the PLM test50 because we believed thatconcurrent movement disorders such as hypokinesiaand akinesia would make it difficult to ascertain thecontribution of balance disorders to these test results.There is, however, a need for future research to addressthe impact of balance disturbance in people with PD onperformance of functional tasks such as walking, turn-ing, and standing from a sitting position. Finally, themost notable limitation of our investigation was thatsubjects were tested at peak dosage during the medica-tion cycle. It is likely that there would be more variability

within and between subjects if tests were administered atthe end of dose or if medication were withheld. Thetests, therefore, may be less likely to discriminatebetween people with PD who fall and those who donot fall.ConclusionPerformance on the tandem stance, single-limb stance,functional reach , and external perturbation tests showeddifferences in balance between subjects with PD andcomparison subjects and between subjects with PD withand without a history of falls. In addition, performanceon these tests was highly consistent from one week to thenext, provided that the subjects were measured at peakdosage dur ing the levodopa cycle. This battery of 4 tests,therefore, appears to be useful for assessing balance inpeople with PD in the clinical setting and may assist inthe prediction of falls in this population. Although thestep test discriminated among groups and yielded con-sistent scores over time, the possibility that hypokinesiacontributed to the results could not be excluded. Fur-ther research is needed to examine the extent to whichthese tests predict falls in larger samples of subjectswith PD.AcknowledgmentsWe thank the Geriatric Research Unit at Kingston Cen-tre for their support, the participants of this study fortheir time and commitment, Ms Winnie Tang, PT, forher valued work as research assistant and examiner , thephysical therapists at Kingston Centre for their supportand comments on the manuscript, and Dr ThomasMatyas for his statistical advice.ReferencesMorris ME, Iansek R. Characteristics of motor disturbance in Parkin-son's disease and strategies for movement rehabilitation. Humanhfouem ent Science 1996;15:649-669.2 Marsden CD. Neurophysiology. In: Stern GM, ed. Parkin son? DiseaseBaltimore, Md: Th e Johns Hopkins University Press; 1990:57-98.

Horak FB, Nashner LM Nutt JG. Postural instability in Parkinson'sdisease: motor coordination and sensoIy organization. Neurology Repurr1988;12:54-55.4 Bloem BR. Postural instability in Parkinson's disease. Clin NeurolAreurosurg 1992;94:S41-S45.5 Boh ann on RW, Larkin PA, Cook AC, et al. Decrease in timed balancetest scores with aging. Phys Ther 1984;64:1067-1070.6 Briggs RC, Gossman MR, Birch R, et al. Balance performance amon gnoninstitutionalized elderly women. Phys Ther 1989;69:748-756.

Goldie PA, Matyas TA, Spencer KI McGinley RB ostural control instanding following stroke: test-retest reliability of some quantitativeclinical tests. Phys Ther 1990;70:234-243.8D un ca n PW, Studenski SA, Cha ndl er JM, Prescott B. Functionalreach: predictive validity in a s ample of elder ly male veterans. JGerontol1992;47:M93-M98.9 Duncan PW, Weiner DK, Cha ndl er JM, Studenski SA. Functionalreach: a new clinical measure of balance. J Gerontol 1990:45:192-197.

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LO Hill K, Bernhardr J , McGann A, et al. A new test of dynamic 31 Cunnington R, Iansek R, Johnson U Bradstla\\, JL. hlovemenstanding balance for stroke patients: reliability, validin, and quantita- related potentials in Parkinson's disease: motor iniagrn and movtive clinical tests. Phjsiothn-apj Cnnadcr. 1996;47:2.57-262. nlent preparation. Brain. 1097:120: 1339-1353.11 M'einer DK. Duncan PW, Chandler JM, St i~ dr l~ sk iA. Fu~~ctionalreach: a nlarker of physiral frailh. ] A m C;oic~tr or. 1992;40:20:%207.12 wolf so^^ LI, h'l~ippleR, Amrrn~anP, Klei~lbergA. Stressing thepostural response: a quantitative ruethod for testing balance. J AmCm'a tr Sor. 1986;34:845-850.13 Chandler JM, Duncan PM', Studenski SA. Balance performance o nthe postural stress test: compariso~~f young adults, healthy elderly,and fallers. Phys Thm. 1990;70:410-41.5.14 Hill K, Vandenwort A, lirarnerJ. Reproducibilih of performance o na test of postural responses in healthy elderly frn~ales. hysiolhmapyCanada. 1990;42:62-66.15 Pastor hM, Day BL, Marsden CD. Vestibular induced posturalresponse in Parkinson's disease. Bm in . 1993;116:11 77-1 190.16 Weiner U , Nora LM, Glanu RH. Elderly i~~patients:ostural reflexirnpairn~ent. eurology. 1984;34:945-947.17 Berg KO, Maki BE, Williams J1, e t al. CXinical an d laboratorynlrasures of postural balance in an elderly population. Arrh Phys MedRohohtl. I YY2;73: 1073-1080.18 Tinetti ME. Performan ceurien tated assessnlent of mobility p r o ble111s n elderly patient$. JAnl Gpn'crtr Sor. 1YH6;34:119-126.19 Podsiadlo D, Richardson S. Th e timed up and go test. A r r h P h ~ r~U vd ehnhil. 1989;67:387-389.20 Dettlnann M Linder M, Sepic S. Relationships among walkingperformance, postural stability, and functional assessments of thehemiplegic patient. A I ~P h ys M ed. 1987;66:77-90.21 Martill B. Evaluation of walking speed and functional ambulationcategories in geriatric day hospital patients. Clinical RPhabilitation.1996;10:44-46.22


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1998; 78:577-592.PHYS THER.Fiona Smithson, Meg E Morris and Robert IansekParkinson's DiseasePerformance on Clinical Tests of Balance in

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phys ther 1998 smithson 577 92

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