Human Movement Science 29 (2010) 831–842

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Human Movement Science

journal homepage: www.elsevier .com/locate/humov

Prioritizing gait in dual-task conditions in peoplewith Parkinson’s

Pamela Fok a,*, Michael Farrell b, Joan McMeeken a

a School of Physiotherapy, The University of Melbourne, Australiab Howard Florey, The University of Melbourne, Australia

a r t i c l e i n f o a b s t r a c t

Article history:Available online 19 August 2010

PsycINFO classification:32973380

Keywords:Parkinson’s diseaseWalkingSelective attentionPhysical therapyDisability managementNeurological disordersBrain damage

0167-9457/$ - see front matter � 2010 Elsevier B.doi:10.1016/j.humov.2010.06.005

* Corresponding author. Address: 60 King Arthu+61 3 95876899.

E-mail address: pamfok@gmail.com (P. Fok).

This controlled study examined the effects of a gait prioritizationstrategy on walking in people with Parkinson’s disease (PD). Partic-ipants in the training group (n = 6) received 30-min therapy to pri-oritize their attention to take big steps while performing serialthree subtractions. Participants in the control group (n = 6)received no therapy. Stride length, gait velocity, and accurate enu-meration rate were measured at baseline, immediately after train-ing and 30 min after training under both single-task (walk only orsubtract only) and dual-task (walk and subtract) conditions. Per-formance was also assessed during therapy for the training group.Stride length and gait velocity increased immediately when partic-ipants followed instructions to prioritize their attention to take bigsteps (p = .005, p = .04). Further, the gait variables increased forboth single and dual-task conditions for at least 30 min after train-ing when compared to the controls; with a simultaneous reductionin the magnitude of dual-task interference (p = .03, p = .03). No dif-ference in the accurate enumeration rate was found at any of theassessment time points. Therefore, prioritizing attention to takebig steps can be an effective strategy to increase the stride lengthand walking speed in some people with PD.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

People with Parkinson’s disease (PD) often direct their attention to walking, particularly in takingbigger strides, to counteract their usual slow and short footsteps (Jones et al., 2008). This strategy is

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r Drive, Glen Waverley, Victoria 3150, Australia. Tel.: +61 3 95876766; fax:

832 P. Fok et al. / Human Movement Science 29 (2010) 831–842

convenient, requires no external equipment, and can deliver prompt and desirable effects (Behrman,Teitelbaum, & Cauraugh, 1998; Canning, 2005; Lehman, Toole, Lofald, & Hirsch, 2005; Morris, Iansek,Matyas, & Summers, 1996). It is endorsed by many experts and in clinical guidelines (European RES-CUE Consortium, 2004; Keus et al., 2004; Morris et al., 1997). However, some clinicians recommendthat dual-task walking should be avoided when using such attentional strategies (Keus et al., 2004;Morris et al., 1997; Rochester et al., 2005), because performing a second task takes attention fromwalking and affects gait further for people with PD. This is also called dual-task interference (O’Shea,Morris, & Iansek, 2002).

The recommendation is questionable, as two recent publications have reported a positive associa-tion between using a gait prioritization strategy (focusing one’s attention to walking with big stepswhen undertaking dual tasks) and the amelioration of gait deficits (Baker, Rochester, & Nieuwboer,2007; Canning, 2005). In the studies conducted by Canning (2005) and Baker et al. (2007), people withPD walked faster and with longer steps as soon as they followed the instructions to prioritize attentionto taking big steps when carrying a tray with glasses, compared to baseline when no specific instruc-tions were given. The mean value of the improved stride length and gait velocity was not significantlydifferent from that of those obtained under a single-task condition (walking only) at baseline (Can-ning, 2005), nor that obtained from the matched healthy controls under a dual-task condition at base-line (Baker et al., 2007). No significant adverse effect was noted on the performance of the secondarymotor task. In reality, it is of prime importance to be able to handle the demand of single task, dualtasks, and multiple tasks during walking in functional environments (World Health Organization,2001) and therefore the feasible options for people with PD to attain these functional abilities shouldbe further explored.

The gait prioritization studies used non-controlled designs, and their findings could be confoundedby non-experimental variables such as participants’ expectations and researchers’ biases. Althoughthere is evidence from these studies that gait prioritization can assist people with PD to walk with fas-ter and with longer steps while performing a second motor task, it is not known if this strategy isequally effective when the second task is cognitive in nature. The effects of gait prioritization onthe severity of dual-task interference also require investigation.

Our study explored the immediate and short-term effectiveness of the gait prioritization strategy,using a controlled experimental design, in people with PD while they are combining a cognitive taskwith walking. We predicted that those who prioritized their attention to taking big steps would beable to walk faster and with longer strides. We also predicted that after 30-min training using gait pri-oritization, they would continue to walk faster and with longer steps in the short-term withoutinstructional prompting. In addition, the magnitude of dual-task interference would decrease. TheUniversity of Melbourne (reference number 060128 and 0718399) and the Southern Health HumanResearch Ethics Committee (reference number 051328) approved this investigation and all partici-pants provided informed consent prior to data collection.

2. Methods

2.1. Research design

This investigation was a single-session laboratory study using a non-randomized mixed design,with one between-subject factor (group) and two within-subject factors (task, time) (Fig. 1). There weretwo levels for the group factor (training group and control group), two levels in the task factor (singletask and dual tasks) and three levels for the time factor (baseline, post-training, and delayed retention).The single-task condition involved either walking only or performing the cognitive task only, while thedual-task condition required walking and performing the cognitive task at the same time.

2.2. Participants

Twelve participants, all with PD (training group n = 6, control group n = 6) were recruited inthe state of Victoria, Australia through our advertisements in regional Parkinson support groups,

2 x = the two repet it ions of the 12 met re walk, subt ract ion task and dual-tasks

* random ised task condit ion

Training group

30-m in t raining using gait pr ior it izat ion

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2 x walking*

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2 x dual- tasks*

Delayed retent ion

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2 x subt ract ions*

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Post - t raining

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2 x subt ract ions*

2 x dual- tasks*

Control group

30-m in sit t ing down reading m agazine

Fig. 1. Schematic representation of the research design.

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community newspapers and the University of Melbourne staff news, and referrals from neurologists.To be eligible, individuals had to be diagnosed with idiopathic PD, have subjective walking difficulties,and be able to walk without assistance for at least 12 m for 25 times. They were without cognitiveimpairment; as indicated by a score of P24 on the Mini-Mental Status Examination (Folstein, Folstein,& McHugh, 1975). Individuals whose walking difficulties were confounded by severe motor fluctua-tion, severe dyskinesia, or co-morbidities were excluded. Individuals who have hearing impairmentwere also excluded as it might affect their ability to follow researchers’ instructions.

In addition, six healthy volunteers were enlisted from the acquaintances of the PD participants andthe researchers, in order to provide criterion stride length to the participants in the training group.Healthy and PD individuals were matched according to gender, age (±2 years), and height (±5 cm).We measured the criterion stride length prior to commencing our investigation with the PD partici-pants. We asked the healthy volunteers to walk indoors along a 12-m walkway at their comfortablepace and their stride length was obtained by dividing the distance with the stride number.

2.3. Secondary task

We used serial three subtractions (counting backwards by threes aloud) as the secondary task. It isa verbal-cognitive task which has previously resulted in significant gait interference in people with PDwhen combined with walking (Hausdorff, Balash, & Giladi, 2003; O’Shea et al., 2002; Yogev et al.,2005). Participants were given a new 3-digit number from a list of 40 random numbers between150 and 450 each time they commenced a testing trial (beginning number).

2.4. Measurement tools and outcome measures

A Panasonic video camera (Panasonic Corporation, Secaucus, NJ, USA) operating at 25 Hz was usedto record the data collection process. Stride length (m) and gait speed (m/s) were the outcome vari-ables for the walking performance, computed by an 8.35 m long � 0.89 m wide GAITRite mat (CIR Sys-tem Inc., Havertown, Philadelphia, USA) and coupled software. The mat was embedded with 27,648

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sensors operating at a sampling rate of 60 Hz. It was placed in the middle of a 12-m walkway to min-imize errors from natural acceleration and deceleration. The GAITRite system has good repeated mea-sures of reliability and excellent concurrent validity with other validated tools (McDonough, NBatavia,Chen, Kwon, & Ziai, 2001). Accurate enumeration rate was the outcome variable for the cognitive taskperformance, calculated by dividing the number of accurate enumerated figures over the ambulationtime across the GAITRite mat (f/s).

3. Experimental procedure

This investigation required participants to attend a single testing session that lasted for approxi-mately 2.5 h. The training group was tested at the gait laboratory in the Geriatric Research Unit, Kings-ton Centre, whereas the control group was tested in a laboratory of similar design at the School ofPhysiotherapy, the University of Melbourne. Same equipment was used at each site. In order to min-imize potential confounding effects caused by levodopa-induced motor fluctuations, we scheduled thetesting sessions to coincide with participants’ on periods within their medication cycles (the time peri-ods when PD medication is effective and motor function is optimal), which commenced an hour aftertheir usual dose of medication and confirmed by a physiotherapist. Participants were given one walk-ing practice trial and one subtraction practice trial before data collection. A 2-min rest was allowedbetween consecutive testing trials throughout the session to prevent fatigue.

Task performance was assessed at baseline, immediately after training (post-training), and 30 minafter training (delayed retention). Testing trials at each assessment time point were conducted undersingle-task and dual-task conditions in randomized order to control for series effects. Two trials wereperformed for each condition and the average was used for data analysis. Standardized verbal instruc-tions were given to participants at the commencement of each trial. The instructions for walking were‘‘walk to the end of the walkway at a comfortable pace”. The instructions for subtraction were ‘‘countbackwards by threes until I tell you to stop, start with (a beginning number)”. The instructions for dualtasks were ‘‘walk to the end of the walkway at a comfortable pace, count backwards by threes, startwith (a beginning number)”.

Dual-task walking training using gait prioritization lasted for 30 min and comprised two segments.First, participants were made known of their criterion stride lengths, marked on the floor with whitelaminated strips perpendicular to the direction of walking for a distance of 5 m. They then steppedover the marked pathway for a few times to obtain familiarization, as the criterion was required forthe subsequent dual-task walking practice. Second, participants practised walking over the 12-mwalkway for 10 trials while performing the subtraction task. Standardized verbal instructions were gi-ven at the commencement of each of these trials, ‘‘walk to the end of the walkway with big steps,count backwards by threes, focus 100% on big steps. Start with (a beginning number)”. For the initialfive practice trials, three white strips corresponding to two criterion steps were placed at both ends ofthe walkway, and were removed thereafter. Task performance was also assessed during dual-taskwalking practice.

3.1. Data analysis

The statistical package for social sciences (SPSS) version 16 (SPSS Incorporation, Chicago, Illinois,USA) was used for data analysis. Results obtained in the studies were considered as statistically sig-nificant at alpha value 6.05. Between-group differences for participants’ clinical characteristics werecompared using independent-samples t-test. Group and task effects for all outcome variables at base-line were tested with 2 (Group) � 2 (Task) univariate repeated measures analyses of variance (ANO-VA). To assess the immediate effects of gait prioritization, the outcome scores at the first twopractice trials during training were compared to the baseline dual-task scores using paired t-tests.To assess the training effects of gait prioritization, outcome variables were analyzed using 2(Group) � 2 (Task) � 3 (Time) univariate ANOVAs, with the last two factors being repeated measures.Greenhouse–Geisser correction was employed when the results obtained from the Mauchly’s test ofSphericity indicated a violation of the sphericity assumption (p 6 .05). Consequent to the statistical

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findings of significant Time � Task � Group interaction, post hoc paired t-tests were performed. Thep-values from these paired t-tests were corrected using the Ryan–Holm–Bonferroni procedure. Theeffect size of training was computed in the natural unit of the gait parameter with the use of the Com-prehensive Meta Analysis (CMA) statistical software version 2.0 (Biostat™, Englewood, NJ, USA). It isexpressed as the mean difference (95% CI) between the outcomes of the retention tests (average scoreof the post-training test and the retention test) and the baseline test (Rosenthal & Rubin, 1986). Theweighted mean of the individual effect size for the two different task conditions were pooled togetherto obtain the overall effect size. Cohen’s d was estimated to describe the size of the effect relative tothe pooled standard deviation before and after training (small effect: d = .2, medium effect: d = .5, largeeffect d P .8) (Cohen, 1988).

4. Results

All participants complied with the testing protocols and completed the session without adverse ef-fects. Both the training group and the control group included one man and five women. Independent-samples t-tests revealed no significant differences between groups in age, height, disease duration,disease severity, mental status, and daily Levodopa intake (Table 1). The mean values and standarddeviations of the outcome variables by time, task, and group are presented in Table 2.

4.1. Outcome measures at baseline

There was a significant Group � Task interaction for stride length, F(1, 10) = 5.6, p = .04, and gaitvelocity, F(1, 10) = 5.0, p = .05. The training group was more affected by dual-task performance thanthe control group (Fig. 2).

There was a significant effect for task in stride length, F(1, 10) = 11.8, p = .006, and gait velocity, F(1,10) = 103.9, p < .001, but not in enumeration, F(1, 10) = 0.08, p = .79. Participants walked with shorterstride length and slower velocity when subtractions were combined with walking. There were no sig-nificant effect for group in stride length, F(1, 10) = 4.4, p = .06, gait velocity, F(1, 10) = 2.1, p = .18, andenumeration, F(1, 10) = 0.01, p = .92.

4.2. Immediate effects of gait prioritization

There was a significant increase in stride length, t(5) = 4.7, p = .005, and gait velocity, t(5) = 2.8,p = .04, as soon as participants commenced dual-task walking practice using gait prioritization, com-pared to the baseline dual-task walking scores (Table 3). A similar effect was not found for enumera-tion, t(5) = �1.9, p = .12.

Table 1Clinical characteristics. Between group comparison.

Training group Control group Independent -samples t-test

Mean (SD) Range Mean (SD) Range p-value

Age (year) 66.8 (9.0) 55–78 57.7 (12.3) 45–75 0.17Height (m) 1.7 (0.1) 1.6–1.8 1.7 (0.1) 1.6–1.8 0.70PD duration (year) 4.2 (2.4) 0.1–7.0 5.5 (3.8) 0.1–10 0.48HY 2.8 (0.4) 2.5–3.5 2.5 (0.6) 1.5–3.5 0.30UPDRS_I 3.2 (3.1) 0–8 3.0 (2.3) 1–7 0.92UPDRS_III 17.7 (10.9) 9–36 15.3 (5.2) 8–21 0.64PDQ39_C 4.2 (3.1) 0–8 4.7 (2.5) 2–9 0.76PDQ39_M 12.3 (8.7) 5–29 12.5 (8.0) 2–23 0.97MMSE 28.3 (1.9) 26–30 29.2 (1.0) 28–30 0.36Levodopa (mg) 375.0 (334.3) 0–1000 608.3 (285.3) 200–1050 0.37

HY – Hoehn and Yahr stages; UPDRS_I and UPDRS_III – Unified Parkinson’s Disease Rating Scale part I and III score; PDQ39_Cand PDQ39_M – Parkinson Disease’s Questionnaire 39 cognitive and motor sections; MMSE – Mini-Mental Status Examination.

Table 2Mean outcome scores (standard deviation) across time.

Training group Control group

ST DT ST–DT ST DT ST–DT

Stride length (m) T1 1.01(0.21) 0.82(0.30) 0.18(0.10) 1.19(0.14) 1.15(0.18) 0.03(0.11)T2 1.19(0.25) 1.18(0.19) 0.10(0.08) 1.22(0.11) 1.17(0.19) 0.06(0.09)T3 1.16(0.20) 1.09(0.29) 0.06(0.11) 1.23(0.12) 1.17(0.17) 0.06(0.07)

Velocity (m/s) T1 0.91(0.37) 0.68(0.37) 0.23(0.03) 1.11(0.16) 0.97(0.24) 0.15(0.08)T2 1.08(0.32) 1.05(0.27) 0.02(0.11) 1.13(0.16) 1.02(0.25) 0.11(0.10)T3 1.07(0.28) 0.99(0.31) 0.09(0.09) 1.16(0.16) 1.03(0.24) 0.13(0.08)

Accurate enumeration rate (f/s) T1 0.39(0.14) 0.37(0.13) 0.02(0.04) 0.38(0.11) 0.39(0.13) -0.01(0.11)T2 0.43(0.12) 0.36(0.11) 0.08(0.07) 0.46(0.14) 0.44(0.10) 0.02(0.15)T3 0.41(0.15) 0.37(0.11) 0.04(0.07) 0.51(0.07) 0.49(0.12) 0.03(0.09)

ST = single-task, DT = dual-task, ST–DT = dual-task interference.T1 = baseline, T2 = post-training, T3 = delayed retention.

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Fig. 2. Group � Task interaction plots (mean ± standard deviation) at baseline.

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4.3. Carry-over effects of gait prioritization training

There was a significant time by group by task interaction (stride length: F(2, 9) = 5.0, p = .03, Fig. 3;gait velocity: F(2, 9) = 4.9, p = .03, Fig. 4). Participants in the training group walked with longer strides,faster speed, and less interference after gait prioritization training when compared to the controls. Thetime by group interaction was also significant (stride length: F(2, 9) = 24.3, p < .001; gait velocity: F(2,9) = 15.5, p = .001). There was a significant Task � Time interaction for gait velocity, F(2, 9) = 9.8,

Table 3Mean outcome (standard deviation) at baseline and during practice (first 2 trials) for the training group.

Baseline Strategy practice Paired t-test p-value

Stride length (m) 0.82 (0.30) 1.17 (0.19) .005Velocity (m/s) 0.68 (0.37) 0.96 (0.28) .04*

Accurate enumeration rate (f/s) 0.37 (0.13) 0.40 (0.27) .75

* Statistically significant (p 6 0.05).

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training group single-task training group dual-task

control group single-task control group dual-task

Fig. 3. Time � Task � Group interaction plots for stride length.

P. Fok et al. / Human Movement Science 29 (2010) 831–842 837

p = .001, but not for stride length (F(2, 9) = 2.8, p = .08). There was no significant Task � Group inter-action for both stride length (F(1, 10) = 0.7, p = .42) and gait velocity (F(1, 10) = 0.2, p = .70). Main effectfor time was detected in stride length, F(2, 9) = 37.0, p < .001, and gait velocity, F(2, 9) = 30.4, p < .001.Main effect for task was significant and participants continued to walk with shorter strides, F(1,10) = 11.1, p = .008, and slower speed, F(1, 10) = 38.5, p < .001, when subtractions were combined withwalking. There was no significant main effect for group (stride length: F(1, 10) = 1.0, p = .35; gait veloc-ity: F(1, 10) = 0.5, p = .49).

Post hoc paired t-tests revealed an 18% and a 15% increase in single-task stride length in the train-ing group from baseline to post-training, t(5) = 6.7, p = .008, and from baseline to delayed retention,t(5) = 6.3, p = .008; as well as a 19% increase in gait velocity from baseline to post-training,t(5) = 6.6, p = .008. The increase in gait velocity from baseline to delayed retention did not reach sta-tistical significance, t(5) = 3.6, p = .08. For dual-task walking, there was a 44% and a 33% increase instride length (t(5) = 6.0, p = .01; t(5) = 5.2, p = .02), as well as a 54% and a 44% increase in gait velocityrespectively (t(5) = 5.1, p = .02; t(5) = 6.8, p = .008).

The overall effect size obtained from gait prioritization training was large for both stride length(mean difference = 0.2 [0.15, 0.24] m, d = 2.52) and gait velocity (mean difference = 0.21 [0.15, 0.27]m/s, d = 2.23) (Table 4). The positive carry-over effects were noted in every individual who receivedtraining (Figs. 5 and 6).

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Fig. 4. Time � Task � Group interaction plot for gait velocity.

Table 4Effect size for stride length and gait velocity. Fixed effect model.

Task condition Mean difference 95% CI % Weight

Stride length (m) ST 0.17 0.12–0.22 82.2DT 0.32 0.21–0.42 17.8Overall 0.20 0.15–0.24

Gait velocity (m/s) ST 0.17 0.09–0.24 73.3DT 0.34 0.22–0.46 26.7Overall 0.21 0.15–0.27

CI = confidence interval, ST = single-task, DT = dual-task.

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On the contrary, no difference was detected in the control group under both single-task (stridelength: t(5) = 1.0, p = .36; t5 = 1.3, p = .24; gait velocity: t(5) = 0.6, p = .57; t(5) = 1.8, p = .14) anddual-task conditions (stride length: t(5) = 0.5, p = .64; t(5) = 0.6, p = .57; gait velocity: t(5) = 1.7,p = .15; t(5) = 3.1, p = .11).

In relation to subtractions, there was no significant Time � Task � Group, Time � Group,Task � Group and Time � Task interaction (F(2, 9) = 0.2, p = .76; F(2, 9) = 2.2, p = .17; F(1, 10) = 0.7,p = .43, and F(2, 9) = 0.97, p = .4). There was also no significant main effect for time (F(2, 9) = 3.3,p = .09), task (F(1, 10) = 2.0, p = .19) and group (F(1, 10) = 1.0, p = .35).

5. Discussion

This study has provided support for using gait prioritization to improve gait performance in peoplewith PD under multiple task conditions. The benefits of using gait prioritization were immediatelyapparent, and continued to be effective without instructional prompting for 30 min after 30-min train-ing. Giving priority to walking had no detrimental effects on the performance of a concurrent cognitivetask.

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puorg lortnoC puorg gniniarT

ksat-lauD ksat-elgniS ksat-lauD ksat-elgniS

Fig. 5. Change in stride length in individual participant under single- and dual-task conditions across the three testing periods(T1 – baseline, T2 – post-training, T3 – delayed retention). Solid lines represent participants S1–S6 in the training group. Dottedlines represent participants C1 – C6 in the control group.

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Fig. 6. Change in gait velocity in individual participant under single- and dual-task conditions across the three testing periods(T1-baseline, T2-post-training, T3-delayed retention). Solid lines represent participants S1–S6 in the training group. Dotted linesrepresent participants C1–C6 in the control group.

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Our findings agree with previous studies that have shown gait interference in people with PD dur-ing the performance of a secondary cognitive task (Bloem, Valkenburg, Slabbekoorn, & van Dijk, 2001;Camicioli, Oken, Sexton, Kaye, & Nutt, 1998; Campbell, Rowse, Ciol, & Shumway-Cook, 2003; Morriset al., 1996; O’Shea et al., 2002; Yogev et al., 2005). However, no previous investigation has exploredthe adverse effects of a secondary task beyond three single-task and three dual-task walking trials. Itwas not known whether the severity of gait interference would intensify, remain the same or lessenwhen people with PD continued with dual tasks. Our controls completed six single-task and six dual-task walking trials across three assessment time points (baseline, post-training, delayed retention)during the two and a half hour laboratory session. Paired t-tests revealed no difference across timein stride length and gait velocity under both task conditions. Therefore, it appears that in the absenceof using an attentional strategy, repeated walking does not alter walking performance and repeateddual-task performance does not have any negative or positive effects on the initial interference.

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However, in order to make a more definitive conclusion, future investigation should include a biggersample size and incorporate more testing trials.

The immediate improvements in stride length and gait velocity obtained through gait prioritizationare compatible with earlier findings in single-task and dual-motor task attention-related studies(Baker et al., 2007; Behrman et al., 1998; Canning, 2005; Lehman et al., 2005; Morris et al., 1996).The improvements call into question the recommendation that people with PD should avoid perform-ing dual tasks while using an attentional strategy during walking (Keus et al., 2004; Morris et al., 1997;Rochester et al., 2005). Gait prioritization may be a likely compensatory tactic to manage slow andshort footsteps during dual-task walking in people with PD. On the other hand, this study did not de-tect any differences in the performance of subtractions when gait prioritization was used during train-ing compared to baseline. This outcome agrees with Canning (2005) who also reported gaitimprovement and no performance change in the secondary motor task (balancing a tray with fourglasses) when using the strategy. It is therefore likely that the central attentional resources in peoplewith PD are not as limited as has been proposed (Kahneman, 1973; Morris et al., 1997; Rochester et al.,2004). It may be worth nothing, however, that although the enumeration scores for the training groupand the controls are similar at baseline, the difference between the two groups is quite large at post-training and delayed retention (Table 2). The control group appears to perform better than the traininggroup. Insignificant findings could be the result of insufficient power with the small sample size. Thiscalls for future investigation with a bigger sample size.

Neuroimaging studies have shown that extensive cerebral regions besides the basal ganglia and theanterior supplementary motor area can compensate for the impaired motor control in PD. Studiesexamining the performance of sequential finger movements found hyperactivity in the lateral premo-tor cortex, the primary sensorimotor cortex, the posterior supplementary motor area, the parietal cor-tex, the anterior cingulate cortex, and the cerebellum in people with PD when compared to healthyindividuals (Sabatini et al., 2000; Samuel et al., 1997; Wu & Hallett, 2005). Further, Catalan, Ishii, Hon-da, Samii, and Hallett (1999) found that when people with PD performed longer and more complexsequential finger movements than those used in other studies (Sabatini et al., 2000; Samuel et al.,1997; Wu & Hallett, 2005), the neuronal activity of the previously under-active anterior supplemen-tary motor area also increased. Reports of gait-related neuroimaging studies are rare. Hanakawa,Fukuyama, Katsumi, Honda, and Shibasaki (1999) examined regional cerebral blood flow changesusing Tc-hexamethylpropyleneamine oxime and single-photon emission computed tomography inpeople with PD after they walked over visual cues on a treadmill. In conjunction with gait improve-ment, hyperactivity was noted in the right lateral premotor cortex, the posterior parietal cortex andthe cerebellum when compared with healthy controls. Based on both the behavioral findings andthe neuroimaging findings, it is possible to suggest that attentional strategies enlist alternative cere-bral regions to improve gait in PD (Iansek, Bradshaw, & Phillips, 1995). This suggestion awaits corrob-oration by future neuroimaging studies which involve attentional strategies and gait.

Gait training using prioritization appears to be a possible option for walking rehabilitation. This isat odds with some experts’ recommendation that dual-task walking training should be avoided in or-der to prevent falls and injuries (Keus et al., 2004). All participants undertaking training completedtheir sessions without adverse effects. The benefits of training were apparent in all cases. Examinationof individual time courses showed that all participants undergoing training had stride length and gaitvelocity improvement.

A comparison of the data in Tables 2 and 3 suggests that the largest increase in stride length andgait velocity occurred in the first two gait prioritization trials with little increase occurring over therest of the training session. Thus a longer training session (10 m � 10 trials) might not have madeany significant improvement at post-training, compared to what was already attained at the onsetof training (10 m � 2 trials). Nevertheless, increasing the length as well as the number of the trainingsessions may strengthen longer term retention effects, which warrants further investigation. For in-stance, Lehman et al. (2005) found retention effects up to one month with ten sessions of single-taskwalking training (9 m � 60 trials) using the attentional strategy to take big steps. In addition, it isworthwhile to explore in future studies the length of retention effect achieved by 30-min training,similar to the current investigation, by inviting participants back for reassessment in one week andone month.

P. Fok et al. / Human Movement Science 29 (2010) 831–842 841

The severity of initial gait interference may determine the outcome of using gait prioritization. Wedid not detect any improvement in the control group across time; nevertheless this group was alsoless affected by dual-task performance compared to the training group at baseline. It is possible thatthere is a clinical cut-off relating to the magnitude of gait interference for walking training. Since indi-viduals with PD vary greatly in their motor symptoms and not every sufferer with the disease requireswalking rehabilitation, future research should look at establishing a relevant clinical measure and cut-off value for gait training and for participant recruitment into training studies. However, it should beemphasized that the positive training effects obtained in our participants were robust as improvementacross time was noted in every individual who received training, and the effects were not influencedby one or two extreme cases.

5.1. Study limitations

There were some limitations in generalizing the result. The participants in this sample did not havesevere motor fluctuations, severe dyskinesia, and freezing of gait. They were also tested during theiron period. It is suggested that people with PD who have severe motor complications or were testedduring the off period may require more attention to walking (Camicioli et al., 1998), and thereforemay respond differently to gait prioritization. Moreover, none of the participants had cognitiveimpairment. Attentional strategies are traditionally recommended for people with PD who do nothave severe cognitive impairment, as impaired cognitive function may limit one’s capacity to enlistattention, and may subsequently increase the risk of falls (European RESCUE Consortium, 2004; Keuset al., 2004; Morris et al., 1996; Rochester et al., 2005).

6. Conclusion

The daily environment requires our ability to perform multiple tasks while walking. For example,in addition to walking, we have to talk to companions, look out for obstacles and take evasive action,etc. Based on the current findings, traditional recommendations may need to be reconsidered. Avoid-ing dual-task walking while using attentional strategies for people with mild to moderate PD andwithout cognitive impairment may not be necessary in all individuals. Training dual-task walkingmay be considered as a possible treatment strategy. Gait prioritization can be used to improve gaitduring dual-task walking for immediate effects in some people. Gait prioritization can also be incor-porated in walking rehabilitation programs for continuing effects.

Acknowledgments

We acknowledge the contributions of the following persons and organizations: Prof. Meg Morrisprovided ideas in the conception of this investigation. Prof. Robert Iansek and Dr. Anna Murphy al-lowed us to use the gait laboratory and equipment in Kingston Centre. Dr. Graham Hepworth of theStatistical Consulting Centre, the University of Melbourne supplied statistical advice. Mr. Brook Galna,Dr. Yi-Liang Kuo, Dr. Pagamas Piriyaprasarth, and Dr. Yong Hao Pua assisted in data collection. Parkin-son Victoria advertised for participant recruitment. Last but not least, we thank all the volunteers andtheir families for their time and involvement.

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