Walkway Length, But Not Turning Direction, Determines the Six-Minute Walk Test Distance in Individuals With Stroke

806 Walkway Length, But Not Turning Direction, Determines the Six-Minute Walk Test Distance in Individuals With Stroke Shamay S. Ng, PhD, William W. Tsang, PhD, Tracy H. Cheung, BSc (Hons), Josiben S. Chung, BSc (Hons), Fenny P. To, BSc (Hons), Phoebe C. Yu, BSc (Hons) ABSTRACT. Ng SS, Tsang WW, Cheung TH, Chung JS, To FP, Yu PC. Walkway length, but not turning direction, determines the six-minute walk test distance in individuals with stroke. Arch Phys Med Rehabil 2011;92:806-11. Objectives: To examine (1) the effect of different walkway distances, and (2) turning directions on the six-minute walk test (6MWT) in subjects with stroke. Design: A cross-sectional study. Setting: University-based rehabilitation center. Participants: Subjects (N 26) with chronic stroke. Interventions: Not applicable. Main Outcome Measures: Total distance covered and number of turns in the 6MWT with different walkway lengths (10-, 20-, and 30-m walkway distances) and turning directions (turning to affected side and unaffected side); rate of perceived exertion (RPE) using Borg Scale, and heart rate (HR) using handheld pulse oximeter recorded before and immediately after the test. Results: The distance covered and the number of turns in the 6MWT were significantly different between different walkway lengths (P.05), with the longest distance covered and lowest number of turns in the 30-m walkway distance. For all walkway lengths, turning to the affected or unaffected side did not result in significant differences in the distance covered and the number of turns in the 6MWT. Significant increases were found between the pretest and posttest for the HR and RPE (P.05) in all testing conditions. There was no significant effect of walkway distance and turning direction on the change in HR and RPE between the 6 conditions of the 6MWT. Conclusions: Different walkway distances have a significant effect on the distance covered in the 6MWT, whereas turning direction did not significantly affect the distance covered in the 6MWT. Key Words: Rehabilitation; Stroke; Walking. 2011 by the American Congress of Rehabilitation Medicine THE SIX-MINUTE WALK TEST was initially introduced as a simple walking test for patients with respiratory 1 or cardiac problems, 2 measuring their functional walking capacity and endurance in daily activities. Patients being tested are required to walk back and forth on a walkway continuously as From the Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong (SAR), China. Supported by a grant from Hong Kong Jockey Club Charities Trust CADENZA: A Jockey Club Initiative for Seniors. to S.S.N. (5-ZH54). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprint requests to Shamay S. M. Ng, PhD, Dept of Rehabilitation Science, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (SAR), e-mail: Shamay.Ng@inet.polyu.edu.hk. 0003-9993/11/9205-00442$36.00/0 doi:10.1016/j.apmr.2010.10.033 far as they can in 6 minutes. The 6MWT is superior to other tests such as cycle ergometer testing because it involves walking, which is a regular daily functional activity. 2 Also, the 6MWT is simpler and easier to administer, while cycle ergometer testing can only assess exercise capacity in the laboratory and requires expensive and sophisticated equipment that is not easily available. Therefore, the 6MWT has been widely adopted and is now commonly used in clinical studies to measure exercise capacity in patients with cardiorespiratory 2,3 or cardiovascular problems, or both. 2-6 Recently, it has been suggested that the distance covered in the 6MWT can be used as a clinical measure of walking endurance in patients with neurologic disorders, including patients after stroke. The distance covered in the 6MWT has been used to evaluate the effectiveness of exercise programs from 4 to 12 weeks long in improving walking endurance among subjects with mild to moderate stroke, 7 subjects with acute stroke, 8 and subjects with chronic stroke. 9,10 The reliability of the 6MWT was established in studies of patients with subacute 11,12 and chronic 13,14 stroke. Excellent test-retest reliability has been reported for the 6MWT with stroke patients, with intraclass correlation coefficients (ICCs) ranging from.94 to.99. 11-14 The ICCs ranged from.97 to.99 for patients with subacute stroke, 11,12 and from.94 to.99 for those with chronic stroke. 13,14 Moreover, the SEM has been reported as small (SEM%, 4.8) for the 6MWT with stroke patients 12 (SEM%: [SEM/mean] 100). Hence, the distance covered in the 6MWT is considered clinically sensitive for detecting changes in patients with stroke. Although the 6MWT is commonly performed and used as a measurement tool in stroke rehabilitation, the length of the walkway used is not standardized. The walkway was initially designed to be 33m, 1,2 and this has been adopted by some studies. 1,2,13 But different lengths have been adopted in other clinical studies, including 100ft, 8 20m, 11,15 30m, 12,16-18 and 50m. 9 In some published studies, the length was not standardized 19 or even mentioned. 7 Because the walkway length determines the number of turns required to cover a given distance, 6MWT results are presumably affected by the length of the walkway used. The effect of turning direction on the distance covered in the 6MWT by subjects with stroke has also been little studied, although the effect of turning direction on TUG test results has been shown to be significant for subjects with stroke. 20 Heung and Ng 20 have reported that turning to the affected side was significantly quicker in the TUG test than turning to the unaf- HR ICC RPE 6MWT SEM TUG List of Abbreviations heart rate intraclass correlation coefficient rate of perceived exertion six-minute walk test standard error of measurement Timed Up & Go

SIX-MINUTE WALK TEST IN STROKE PATIENTS, Ng 807 fected side in a study of subjects with subacute stroke. On the other hand, de Morais Faria et al 21 found that the performance of subjects with chronic stroke in the TUG test was similar when turning toward the affected and unaffected sides. The effect of turning direction on TUG test results clearly requires further investigation. In view of how stroke-related impairments may affect turning ability, the effect of turning direction in the 6MWT is also worthy of investigation. We hypothesized that with different walkway lengths and turning directions, 6MWT distances covered by individuals with stroke would be significantly different. The objectives of the present study were to investigate (1) the effect of walkway length and (2) the effect of turning direction on the 6MWT distance covered by individuals with stroke. METHODS Participants This study was a clinical trial with a 2 3 experimental design, with analysis of 2 independent variables of walkway length and turning direction on the distance covered in the 6MWT in individuals with stroke. According to Blennerhassett and Dite s study, 22 differences of 115m were required to represent significant differences in the 6MWT distance. At least 17 subjects would be needed if the threshold for statistical significance was set at 5% ( level at.05) and the power at 80% ( level at 0.2). Twenty-six subjects (13 men, 13 women; mean age SD, 58.5 6.1y) with a mean SD poststroke duration of 7.0 6.5 years were recruited from a local rehabilitation network in Hong Kong (table 1). Subjects with chronic stroke were recruited if they (1) had sustained a stroke at least 1 year previously; (2) were 45 years or older; (3) were able to walk 10m with or without a walking aid but without personal assistance; (4) had an Abbreviated Mental Test score of 7 or Table 1: Descriptive Characteristics of the Subjects (n 26) Variables n (%) Sex (male/female) 13 (50)/13 (50) Type of stroke (ischemic/hemorrhage) 17 (65)/9 (35) No. of stroke attacks (once/twice) 22 (85)/4 (15) Side of hemiplegia (left/right) 16 (62)/10 (38) Mobility status 15 (65)/7 (27)/2 (8)/2 (8) (unaided/stick/quadripod/umbrella) Anti foot drop device (need orthosis/ 2 (8)/24 (92) no orthosis) No. of falls in past 6mo, 23 (88)/2 (8)/1 (4) (no/once/twice) Mean SD (range) Age (y) 58.5 6.1 (47 67) Body weight (kg) 60.5 12.9 (35.5 85) Height (cm) 158.6 9.7 (127 176) Body mass index (kg/m 2 ) 23.8 3.6 (18.16 31.03) Poststroke duration (y) 7.0 6.5 (1.67 33.17) Median (range) Spasticity level (Modified Ashworth Scale) of hemiplegic ankle plantar flexor Spasticity level (Modified Ashworth Scale) of nonhemiplegic ankle plantar flexor 1 (0 4) 0 (0 0) higher 23 ; and (5) had a stable general medical condition that would allow their participation in the testing protocol. Subjects were excluded if they had received a neurologic diagnosis other than stroke, such as Parkinson s disease or multiple sclerosis, or if they had other comorbid disabilities that might hinder proper assessment. The study was approved by the local ethics committee and conducted according to the Declaration of Helsinki for human experiments. The study procedure was clearly explained to all participates beforehand, and informed, written consent was obtained before the assessments began. Measurements The total distance traveled in 6 minutes, the number of turns, and the amount of rest taken during the 6MWT were recorded. The RPE reflected by the Borg Scale, 24 and the HR were recorded before and immediately after the test. Six-minute walk test. The 6MWTs were conducted along a corridor marked with different walkway lengths: 10m, 20m, and 30m. Colored tape marked the ends of the walkway and each 1-m increment. Standardized encouragements were given at 1, 3, and 5 minutes during the walk: You re doing a good job (minute 1), You re halfway done (minute 3), and You have 1 minute to go (minute 5). 2 To ensure safety, the investigator walked slightly behind but not beside the subjects, so as to avoid influencing their self-selected walking pace. Subjects were allowed to stop and rest as they might deem necessary. The distance covered, to the nearest centimeter, the number of turns, and the amount of rest in 6 minutes were recorded. Rate of perceived exertion. Dyspnea and overall fatigue levels were rated using the Borg scale. 24 Subjects were presented with a printed Borg scale and asked to choose a level that best described their RPE. Heart rate. HR was measured using a handheld pulse oximeter before and immediately after the 6MWT. Procedure Each subject was individually instructed to walk from one mark to the other, covering as many laps as possible at their own walking pace during the allotted time of 6 minutes. Each participant performed the 6MWT under 6 experimental conditions to quantify any effect of course length or turning direction on the distance covered. The 6 conditions were as follows: Condition 1: Turning to the affected side, with a 10-m Condition 2: Turning to the affected side, with a 20-m Condition 3: Turning to the affected side, with a 30-m Condition 4: Turning to the unaffected side, with a 10-m Condition 5: Turning to the unaffected side, with a 20-m Condition 6: Turning to the unaffected side, with a 30-m The subjects performed the 6MWT under the 6 conditions in a random sequence determined by drawing lots. Each subject completed 6 conditions over 3 separate days, with 2 conditions conducted on each day. A 20-minute rest was allowed between conditions. Each subject performed only 1 trial in each condition. Statistical Analysis Descriptive statistics described the demographic characteristics of the subjects. Interactions of different walkway lengths

808 SIX-MINUTE WALK TEST IN STROKE PATIENTS, Ng Table 2: Mean Distance Covered in the 6MWT in Each Testing Condition Walkway Length (m) Distance Covered in the 6MWT (m) Affected Side Unaffected Side P * 10 227.32 79.07 228.8 84.20.624 20 252.2 95.31 255.79 92.14.368 30 265.47 94.16 269.35 107.75.467 NOTE. Values are mean SD or as otherwise indicated. *Effect of turning direction analyzed by paired t test. and turning directions were sought using linear mixed models. There was no significant interaction between turning direction and walkway length in terms of the distance covered. Thus, the main effects relating turning direction and walkway distance could be interpreted directly. Differences in distance covered, the number of turns, and changes in HR during the 6MWT were analyzed by paired t tests with 2 different turning directions, and 1-way analysis of variance with repeated measures followed by the Bonferroni post hoc multiple comparison test with 3 different walkway lengths, respectively. The Wilcoxon s signed-rank test was used to analyze the changes in RPE in different walkway lengths. The difference in HR before and after each of the conditions was analyzed with paired t tests, while the Wilcoxon signed-rank test was used with the RPE reading. The analysis used the Statistical Package for the Social Sciences software. a RESULTS Distance Covered and Number of Turns in 6MWT The mean SD distance covered in the 6MWT and the number of turns in each testing condition are summarized in tables 2 and 3, respectively. No significant difference in either the mean distance covered or the number of turns was observed between turning to the affected and the unaffected side with any walkway length (tables 2 and 3). There were, however, significant differences in the mean distance covered and the number of turns with different walkway lengths (P.001) (figs 1 and 2). Heart Rate and Perceived Exertion Before and After the 6MWT Significant differences were found in the subjects pretest and posttest HRs and RPEs in all 6 conditions (table 4). In addition, no significant difference could be found in the change of HR or RPE when comparing turning to the affected and unaffected side, and when comparing different walkway lengths (table 4). Fig 1. Mean distance covered in the 6MWT in each testing condition. *Statistically significant difference between walkway lengths (P<.05). DISCUSSION This is the first study to investigate the effect of turning direction and walkway length on the distance covered in the 6MWT in individuals with chronic stroke. Distance Covered in 6MWT The mean distances covered during the 6MWT were consistent with those found in some studies that used the same walkway length in patients with stroke, 12,16-18 but were slightly different from the distances reported by other studies. 11,15 No previous study used a 10-m Two studies 11,15 used a 20-m walkway with stroke subjects, and the mean distances reported were 196m 11 and 216m, 15 which are both shorter than the distances found in the present study. This might be explained by differences in the characteristics of the subjects. The subjects in the present study were younger than those in previous Table 3: Mean Number of Turns in the 6-Minute Walk Test in Each Testing Condition No. of Turns in the 6MWT Walkway Length (m) Affected Side Unaffected Side P * 10 22.31 7.86 22.46 8.49.627 20 12.19 4.84 12.23 4.72.832 30 8.46 3.11 8.5 3.49.824 NOTE. Values are mean SD or as otherwise indicated. *Effect of turning direction analyzed by paired t test. Fig 2. Mean number of turns in the 6MWT in each testing condition. *Statistically significant difference between different walkway lengths (P<.001).

SIX-MINUTE WALK TEST IN STROKE PATIENTS, Ng 809 Table 4: Heart Rate and Rate of Perceived Exertion Before and After the 6-Minute Walk Test in Each Testing Condition Testing Conditions* Pretest Posttest Change % Change Condition 1 HR (bpm) 65.62 9.58 72.77 10.22 7.15 7.57 11.57 11.80 RPE 9.08 2.65 9.73 3.01.65 1.02 7.04 10.88 Condition 2 HR (bpm) 64.23 9.63 72.54 9.98 8.31 8.23 13.94 14.42 RPE 8.85 2.46 9.46 2.97.62 1.13 6.49 11.96 Condition 3 HR (bpm) 64.23 9.98 74.19 12.61 9.96 9.30 16.18 15.48 RPE 9.23 2.94 10.15 3.27.92 1.16 10.37 13.60 Condition 4 HR (bpm) 62.46 8.44 72.81 11.95 10.35 11.26 17.75 19.08 RPE 8.85 2.60 9.69 3.06.85 1.62 13.73 29.47 Condition 5 HR (bpm) 65.04 8.53 71.73 11.96 6.69 10.65 10.95 16.41 RPE 8.88 2.42 9.42 3.09.54 1.21 5.09 11.40 Condition 6 HR (bpm) 63.62 6.89 72.73 11.97 9.11 9.83 14.49 16.63 RPE 9.38 2.61 1.12 2.92.73 1.22 8.02 14.42 Mean of 6 conditions HR (bpm) 64.20 1.01 72.80.72 8.60 1.35 14.15 2.39 RPE 9.045.20 9.76.29.72.13 8.46 2.85 Abbreviation: bpm, beats per minute. *Condition 1: Turning to the affected side, 10-m Condition 2: Turning to the affected side, 20-m Condition 3: Turning to the affected side, 30-m Condition 4: Turning to the unaffected side, 10-m Condition 5: Turning to the unaffected side, 20-m Condition 6: Turning to the unaffected side, 30-m Paired t tests were used to analyze pretest and posttest HRs. Wilcoxon signed-rank test was used to analyze pretest and posttest RPE differences. Indicates a difference significant at the 5% confidence level. studies (mean age SD, 58.5 6.1y vs 72y), 11,15 and their poststroke duration was longer than that of subjects in previous studies (mean SD poststroke duration, 6.97 6.45y vs 227d). 11,15 There have also been 4 studies 12,16-18 of stroke survivors in which a 30-m walkway was used. The mean distance covered in those studies ranged from 196.4 to 384m. 12,16-18 The mean distance found in the present study fell within that range. Walking endurance as measured by the 6MWT has been reported to be decreased in persons after stroke when compared with the walking endurance of the healthy elderly. 13,25 The 6MWT distance for healthy male and female adults can be predicted using the mathematical equation suggested by Enright and Sherrill. 26 According to the equation, the predicted distance in the present study should be approximately 500m; however, our stroke subjects could only walk about 45% of the predicted distance. This is consistent with the results of a study by Mayo et al 25 that found only 40% of the age-predicted performance in subjects with chronic stroke. This is important because walking endurance as measured by the 6MWT is today the best statistically significant predictor of community integration. 25 Effect of Turning Direction This study is the first to document the effect of turning direction on distance covered in the 6MWT in individuals with stroke. The results show that 6MWT distance was not influenced by turning direction, which is consistent with the results of a previous study 21 that found no effect of turning direction on TUG test times. The mean SD poststroke duration (52.2 49.2mo) and the mean age SD (54.73 5.42y) of the subjects in that previous study 21 were similar to those in the present study. A previous study by Heung and Ng 20 did, however, find a significant effect of turning direction in the TUG test. There are some possible reasons for the difference in findings. The subjects of the present study were younger than those in Heung and Ng s work (mean age SD, 58.5 6.1y vs 66.12 6.15y), and Heung and Ng s subjects 20 had subacute stroke (mean SD poststroke duration of only 87.8 40.4d). 20 Subjects with more acute stroke might be expected to have poorer motor function. 27 The insignificant effect of turning direction on distance covered in the 6MWT suggests some interesting observations about compensation. Current literature on turning mechanics in individuals with stroke is lacking. Results of a clinical study with 55 subjects older than 64 years 28 showed that elderly subjects with balance dysfunction took more steps during turning, turned more slowly, and had longer TUG test scores compared with those without balance difficulties. Thigpen et al 28 concluded that an increase in the number steps during turning was 1 characteristic of turning difficulty in the elderly population. It is plausible that the number of steps used in turning could determine the time taken in turning, and determines 6MWT distance. In the current study, subjects with stroke were observed to take more steps when turning to either affected or unaffected sides, although the number of steps during turning was not formally recorded. This increase in the number of steps contributed to a longer turning time and thus a shorter 6MWT distance. However, this hypothesis requires further investigation with an instrumented walkway or a 3-dimensional motion analysis system

810 SIX-MINUTE WALK TEST IN STROKE PATIENTS, Ng to confirm it. It would also be interesting to study a large number of stroke patients, allowing them to freely choose their preferred turning direction, but that was not attempted in this study. Effect of Walkway Length Walkway length is, of course, inversely proportional to the number of turns taken during the test (see fig 2). Total distance covered should thus be affected by walkway length. The greater number of turns required on a shorter walkway (see table 3) calls for more time and effort. Moreover, a longer walkway allows more room for acceleration and higher top speeds if the subject can manage them. In a clinical study with 34 older adults, Macfarlane and Looney 29 showed that a minimal walkway length for acceleration (2.17 3.23m) and deceleration (1.80 1.85m) was required to achieve a steady walking speed during the walking test. Beyond these physical considerations, however, walkway length might invoke some psychological factors that influence a subject s self-selected walking pace. In a clinical trial with 27 older adults, Najafi et al 30 showed that older people presumably choose a higher gait speed strategy over a longer walkway distance ( 20m), but a slower gait speed strategy if walking over a shorter walkway distance ( 10m). Both of these findings on healthy older adults require further research to confirm them in subjects with stroke who have stroke-specific impairments. Heart Rate and Perceived Exertion Performing the 6MWT increased both HR and RPE (see table 4). The increases were comparable to those reported in a previous study 31 where HR increased by 15% in subjects with subacute stroke. The increase in HR suggests that the 6MWT does indeed put strain on the cardiovascular system. 16 The turning direction and walkway length had no significant effect on the changes in HR and RPE, even with the significantly different distances covered. It seems that the extra distance walked on a longer walkway did not further stress the cardiovascular system. Study Limitations Strictly speaking, our results should only be applied to subjects with stroke who fulfill similar inclusion criteria, because of the small sample size in our study. In addition, our results should only be applied to similar environments: indoors with a smooth tile floor, but not, for example, to carpeted walkways. Note that the design of the present study was cross-sectional. No causal relationship was established. This study design was not able to show which walkway length was optimal for assessing patients with stroke. It was able to show only the effect of different walkway lengths on the distance covered in the 6MWT. For valid and reliable comparisons (eg, between pretreatment and posttreatment conditions), testing and retesting should be performed under identical distance conditions. Whether the use of a circular pathway for the 6MWT would be a more reliable and valid measurement warrants further study. Investigators had to walk closely behind these subjects for safety reasons, which may have influenced the pacing of the subjects. Also, there might have been a certain degree of learning effect, because each subject had to perform the test 6 times in the 6 different conditions. However, the randomization of testing sequences and the performance of the tests on separate days were intended to reduce any learning effect. Moreover, the results of a previous study 11 did not support a practice effect across 2 trials of the 6MWT in people with stroke. 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