5-Repetition Sit-to-Stand Test in Subjects With Chronic Stroke: Reliability and Validity

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5-Repetition Sit-to-Stand Test in Subjects With Chronic Stroke: Reliability and Validity Yiqin Mong, MSc, Tilda W. Teo, MSc, Shamay S. Ng, PhD ABSTRACT. Mong Y, Teo TW, Ng SS. 5-repetition sit-tostand test in subjects with chronic stroke: reliability and validity. Arch Phys Med Rehabil 2010;91:407-13. Objectives: To examine the (1) intrarater, interrater, and test-retest reliability of the 5-repetition sit-to-stand test (5repetition STS test) scores, (2) correlation of 5-repetition STS test scores with lower-limb muscle strength and balance performance, and (3) cut-off scores among the 3 groups of subjects: the young, the healthy elderly, and subjects with stroke. Design: Cross-sectional study. Setting: University-based rehabilitation center. Participants: A convenience sample of 36 subjects: 12 subjects with chronic stroke, 12 healthy elderly subjects, and 12 young subjects. Interventions: Not applicable. Main Outcome Measures: 5-Repetition STS test time scores; hand-held dynamometer measurements of hip flexors, and knee flexors and extensors; ankle dorsiflexors and plantarflexors muscle strength; Berg Balance Scale (BBS); and limits of stability (LOS) test using dynamic posturography. Results: Excellent intrarater reliability of intraclass correlation coefficient (ICC) (range, .970 –.976), interrater reliability (ICC⫽.999), and test-retest reliability (ICC range, .989 –.999) were found. Five-repetition STS test scores were also found to be significantly associated with the muscle strength of affected and unaffected knee flexors (␳⫽–.753 to –.830; P⬍.00556) of the subjects with stroke. No significant associations were found between 5-repetition STS test and BBS and LOS tests in subjects with stroke. Cut-off scores of 12 seconds were found to be discriminatory between healthy elderly and subjects with stroke at a sensitivity of 83% and specificity of 75%. Conclusions: The 5-repetition STS test is a reliable measurement tool that correlates with knee flexors muscle strength but not balance ability in subjects with stroke. Key Words: Muscle strength; Rehabilitation; Stroke. © 2010 by the American Congress of Rehabilitation Medicine HE SIT-TO-STAND TEST was initially introduced as an T outcome measurement for functional lower limb muscle strength. The 5-repetition STS test was first used as a physical 1

differentiate older adults (age range, 63–90y) with and without balance dysfunction.3 It was also used as an outcome measure for evaluating effectiveness of intervention in subjects having total hip and knee arthroplasty4 and vibration therapy5 and for cross-sectional correlation studies in subjects with osteoarthritis6,7 and vestibular dysfunction.8 The 5-repetition STS test has also been introduced as an outcome measure in studies investigating strength training and functional performance in subjects with chronic stroke,9,10 as well as cross-sectional studies evaluating the association of disabilities and falls in population with stroke.11,12 Despite the common use of the 5-repetition STS test, test-retest reliability (ICC range, .890 –.960) was established in healthy older adults13,14 and elderly with osteoarthritis (ICC⫽.960)7 but not in subjects with stroke. Besides lower limb muscle strength, balance capacity of subjects could also affect sit-to-stand performance.13,15 From a sitting position, more horizontal momentum was required to shift the posterior-located center of mass to rise to a standing position,16 which demanded relatively good balance control.17 Stroke-specific lower limb muscle weakness18-20 and balance impairments21-23 could lead to poor sitting to standing performance; however, the relationship between 5-repetition STS test scores and balance performance was unclear. The objectives of the present study were (1) to investigate the intrarater, interrater, and test-retest reliability of the 5-repetition STS test in subjects with chronic stroke; (2) to investigate the relationship between the 5-repetition STS test and BBS, lower limb muscle strength, and the measurements of LOS in subjects with stroke; and (3) to determine the sensitivity of the 5-repetition STS test in distinguishing differences in mobility among subjects with stroke, healthy elderly, and young subjects. METHODS Participants An ICC value of .957 for the 5-repetition STS test was previously shown in healthy subjects14; thus, the ICC value for subjects with stroke was hypothesized to be .930. Therefore, to detect an ICC value of .930 at a significance level of .050 for test-retest reliability, a sample size of 12 subjects was required to achieve 93% power of 2 observations a subject.

performance measure to detect the associations with prediction of mortality and disabilities in frail elderly2 as well as to List of Abbreviations From the Department of Physiotherapy, Tan Tock Seng Hospital (Mong), and Inpatient Therapy Services, St Andrew’s Community Hospital (Teo), Singapore; and the Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hong Kong (SAR), China (Ng). 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. Ng, PhD, Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (SAR), e-mail: [email protected]. 0003-9993/10/9103-00472$36.00/0 doi:10.1016/j.apmr.2009.10.030

AUC BBS COP ICC LOS MVL MXE 5-repetition STS test RT

area under the receiver operating characteristic curve Berg Balance Scale center of pressure intraclass correlation coefficient limits of stability movement velocity maximum excursion 5-repetition sit-to-stand test reaction time

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Convenience sampling was used to recruit 36 subjects, with 12 subjects in each of the 3 subjects groups: stroke, healthy elderly, and young. Young subjects were recruited to determine the cut-off score of the 5-repetition STS test. All subjects had to be able to stand up independently from a chair without hand support. Subjects with stroke were included if they were at least 1-year poststroke, were older than 50 years, were medically stable, were able to ambulate more than 10m unassisted with or without a walking aid, and had an Abbreviated Mental Test24 score of more than 7. Exclusion criteria were the presence of any cerebellar involvement or other conditions that might affect muscle strength, balance, mobility status, or ability to follow instructions. All subjects recruited in the healthy elderly and young groups had to be more than 50 years of age or between 21 and 35 years old, respectively. Subjects having any conditions that might affect the assessment protocol, such as uncontrolled diabetes mellitus, were excluded from the study. All subjects were required to sign written informed consent forms before the commencement of the experimentation. Ethic approval for this study was obtained from the ethics committee of the local institution. Outcome Measurements 5-repetition sit-to-stand test. The 5-repetition STS test measured the time taken to complete 5 repetitions of the sit-to-stand maneuver. All sit-to-stand maneuvers were performed from a chair without an arm rest at 43cm in height and 47.5cm in depth. All trials were videotaped with a videotaping device. The first 2 trials were for familiarization purposes, and the average of the next 3 trials was used for analysis. A 1-minute rest was given between trials to prevent fatigue. Standardized instructions were given as follows: “By the count of 3, please stand up and sit down as quickly as possible for 5 times. Place your hands on your lap and do not use them throughout the procedure. Lean your back against the chair’s backrest at the end of every repetition.” The timing started once the subject’s back left the backrest and stopped once the back touched the backrest. Muscle strength of lower limb. Lower-limb muscle strength was tested with a hand-held dynamometer. Good to excellent reliability (ICC range, .840 –.990)25,26 was reported for lower-limb hand-held dynamometer strength measurements in subjects with neurologic conditions. Isometric muscle strength of hip flexors, knee flexors and extensors, and ankle plantarflexors and dorsiflexors were tested bilaterally with standardized testing positions and dynamometer placement (table 1). Make tests were performed on all muscle groups tested. Subjects were secured on a high chair with safety belts to standardize the assessment positions. The first 2 trials were for familiarization purposes, and the mean reading of the last 3 trials were used for analysis. One to 2 minutes of rest was given between trials to prevent muscle fatigue. Subjects were instructed to “Push against my resistance as hard as you can.” Clinical balance performance: Berg Balance Scale. The BBS was used to assess subjects’ ability to maintain stability.27 Excellent reliability of the BBS (ICC range, .980 –.990)28,29 was found in patients with acute28 and chronic stroke.29 The BBS involves 14 tasks; each has a score between 0 and 4, adding up to a total score of 56. Laboratory balance performance: limits of stability test. LOS was assessed by dynamic posturography (Balance Mastera), which measures the displacement of the COP during voluntary movement in a designated direction without instability.30 A previous study demonstrated moderate reliability (ICC range, .840 –.880) in subjects with chronic stroke.29 Arch Phys Med Rehabil Vol 91, March 2010

Table 1: Muscle Strength Testing Position and Dynamometer Placement Muscle Group Tested

Hip flexors

Knee flexors

Knee extensors

Ankle dorsiflexors

Ankle plantarflexors

Testing Position

Dynamometer Placement

High sitting Hip: 90o flexion Knee: 90o flexion Ankle: neutral High sitting Hip: 90o flexion Knee: 90o flexion Ankle: neutral High sitting Hip: 90o flexion Knee: 90o flexion Ankle: neutral High sitting Hip: 90o flexion Knee: full extension Ankle: neutral High sitting Hip: 90o flexion Knee: full extension Ankle: neutral

On anterior aspect of femur, 5cm proximal to superior border of patella On posterior aspect of tibia, 5cm proximal from inferior tip of medial malleoli On anterior aspect of tibia, 5cm proximal from inferior tip of medial malleoli On ventral aspect of foot, across 1st to 5th metatarsophalangeal joints On dorsum aspect of foot, across 1st to 5th metatarsophalangeal joints

Three parameters of LOS were measured: 1. RT, measured in seconds, refers to the time between the appearance of the signal for movement and the initiation of the first movement.30 2. MVL, measured in degrees a second, is defined as the average speed of COP displacement during the first movement toward the given target.30 3. MXE, expressed as the percentage of the target distance being tested, refers to the maximal displacement of COP during the entire LOS testing for each target.30 Subjects were instructed to “Begin each trial with the cursor in the middle box. On hearing a ‘Ding,’ move the cursors as fast and as accurately as possible into the box where the circle appeared. Shift your body weight to control the position and direction of the cursors. Maintain your balance and keep your feet firmly on the platform throughout the assessment.” Procedures Five trials of the 5-repetition STS test were measured simultaneously by the 2 examiners with 3 years of clinical experience. These trials were videotaped and shown to 3 physiotherapists with 3 to 7 years of clinical experience and 3 tertiary students without a medical or health care background. Procedures for data collection of intrarater, interrater, and test-retest reliability are illustrated in figure 1. The BBS, muscle strength, and dynamic posturography measurements of LOS were tested in random order by either examiner A or examiner B. Statistical Analysis Data analysis was done with SPSS version 17.0.b The Kolmogorov-Smirnov test and F test were used to assess the normal distribution and equal variance of the test score. Descriptive statistics were used for sociodemographic characteristics evaluation. Differences between the mean test score across the 3 groups were calculated by 1-way analysis of variance. ICC was used to calculate the degree of intrarater (ICC3,1), interrater (ICC3,2), and test-retest reliability (ICC2,1). The relationship between the 5-repetition STS test score and

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Fig 1. Procedure of data collection.

the muscle strength of affected and unaffected limbs and balance performance in subjects with stroke was established by the Spearman correlation coefficient because the data were not normally distributed. When multiple correlation tests were performed, the Bonferroni adjustment was applied to adjust for the alpha level.31 In order to assess the correlation between the 5-repetition STS test and 9 primary outcomes (affected and unaffected knee extensors strength, affected and unaffected knee flexors strength, affected and unaffected ankle dorsiflexors, BBS, and maximal excursion in forward and backward direction of LOS), the P value after Bonferroni correction is .05/9 (ie, .00556). The strength of the correlation was defined by the correlation coefficient obtained as little or no (␳⬍.250), fair (␳⫽.250 –.500), moderate to good (␳⫽.500 –.750), or good to excellent (␳⬎.750) relationship.31 A significance level of .050 was set for all analyses. Sensitivity indicates the true-positive probability, whereas specificity indicates the false-positive probability.31 A trade-off between sensitivity and 1 minus specificity was performed using the Youden index32 to obtain the most appropriate 5-repetition STS test cut-off score. The AUC then provides a quantitative measure of the accuracy of the test based on the null hypothesis of AUC equal to 0.5.31 RESULTS Descriptive statistics of all subjects and mean values of all outcome measures are presented in tables 2 and 3, respectively.

Excellent intrarater reliability (ICC⫽.970 –.976) (table 4), interrater reliability (ICC⫽.999), and test-retest reliability of experienced physiotherapists (ICC⫽1.000) and students (ICC⫽.994) were achieved in the present study. Table 5 demonstrates the Spearman correlation analyses of 5-repetition STS test scores in lower limb muscle strength, BBS, and LOS. Five-repetition STS test scores had significant negative correlation after Bonferroni correction with affected (␳⫽–.753; P⫽.005) and unaffected (␳⫽–.830; P⫽.001) knee flexors of subjects with stroke. No significant associations were found between 5-repetition STS test score with BBS and LOS performance in subjects with stroke. Five-repetition STS test cut-off scores of 9.4 seconds and 12.2 seconds were found to be the best discriminators between our young versus healthy elderly (sensitivity⫽75%; specificity⫽75%) and healthy elderly versus subjects with stroke (sensitivity⫽83%; specificity⫽75%), respectively. AUC analysis is shown in figures 2a and 2b. DISCUSSION Reliability of the 5-Repetition Sit-to-Stand Test This is the first study to investigate the intrarater, interrater, and test-retest reliability of the 5-repetition STS test in people with chronic stroke. A better reliability range of the 5-repetition STS test was noted in subjects with stroke (ICC range, .971–.999) than those previously reported in community-dwellArch Phys Med Rehabil Vol 91, March 2010

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5-REPETITION SIT-TO-STAND TEST IN PATIENTS WITH STROKE, Mong Table 2: Mean Values of Demographics and 5-Repetition Sit-to-Stand Test in 3 Subject Groups Mean Values Parameters

Young (n⫽12)

Healthy Elderly (n⫽12)

Demographics Age (y) Sex (M/F) Height (cm) Weight (kg) Body mass index (kg/m2) 5-repetition STS test (s)

26.2⫾2.9 9/3 160.8⫾5.5 57.5⫾11.0 22.1⫾3.4 8.9⫾0.7

56.0⫾3.7 10/3 155.3⫾6.0 57.9⫾11.5 23.9⫾3.8 10.8⫾1.7

P (Post Hoc Comparisons) Stroke (n⫽12)

P

60.0⫾4.8 6/6 157.6⫾12.7 61.6⫾12.1 24.6⫾2.0 17.1⫾7.5

⬍.001* .194 .311 .628 .160 ⬍.001*

Young vs Stroke

Healthy Elderly vs Stroke

⬍.001†

⬍.001*

.013† NA NA NA NA .004*

Young vs Healthy Elderly

⬍.001†

.569

NOTE. Values are mean ⫾ SD. Abbreviations: F, female; M, male; NA, not applicable. *Denotes significant difference at P⬍.05. † Denotes significant difference at P⬍.05 using Tukey Honestly Significant Difference adjustment.

ing elderly (ICC range, .640 –.960)13,14,33-35 and frail elderly (ICC⫽.670).36 Unlike in other studies,13,14,33-36 the experienced and inexperienced assessors were shown video clips of the test on both occasions, and this could have contributed to better reliability by minimizing participant-related factors on the performance of the 5-repetition STS test. The well defined assessment protocol with standardized use of instructions14 and equipment reduced variations in measurements, which could have contributed to the excellent reliability in this study. This was the pioneering study to determine the effect of assessors’ training background on the reliability of the 5-repetition STS test. The results strongly indicated that reliability can be preserved regardless of the assessors’ training background. This could promote the use of the 5-repetition STS test in clinical settings with patients with stroke. The influence of assessors on the reliability of the 5-repetition STS test was formerly reported to be minimal, because assessors were found to contribute .028% to .030% of the estimated source of the variance component.33 Performance of 5-Repetition Sit-to-Stand Test in Subjects With Stroke The mean 5-repetition STS test scores of the subjects with stroke (17.1⫾7.5s) were comparable to timing achieved by participants (17.9⫾7.7s) of a similar age group (approximately 60y)11 but superior to the score (time range, 19.3–23.6s) reported in an older age group (65.8 –70y).9,10,12 It was noted that

the elderly clocked a longer duration for the 5-repetition STS test with increased age.14 Consistent with a previous study,37 the subjects with stroke had a longer sit-to-stand duration because of stroke-specific impairments such as lower-limb muscle weakness38,39 and poor balance.37 Poststroke muscle weakness caused by the failure in motor unit recruitment and a decrease in firing frequency40 as well as localized adaption of paretic muscle fiber41 could impede sit-to-stand performance. Correlations of 5-Repetition Sit-to-Stand Test Scores With Other Outcome Measures Relationship of 5-repetition sit-to-stand test with muscle strength. It is interesting to note the significant correlation between 5-repetition STS test scores and bilateral knee flexors strength (affected ␳⫽–.753; unaffected ␳⫽–.830) in this study. Although previous investigations on the correlation between knee flexors strength and sit-to-stand performance were absent, knee flexors were known to maintain knee joint stability and assist in extending hip joints during sit-to-stand performance.38 It is reasonable to observe an involvement of knee flexors in providing more stability to the knee joint and higher extension force in the hip joint during a fast-paced 5-repetition STS test. In contrast with other studies,9,39 a lack of significant correlations was noted between 5-repetition STS test scores and the other muscle groups (see table 5). Five-repetition STS test scores were previously reported to have significant negative correlations with affected hip flexor,9 affected knee extensor,39

Table 3: Mean Values of All Outcome Measures in Subjects With Stroke (nⴝ12) Mean Values Parameters

Muscle strength (kg) Hip flexors Knee flexors Knee extensors Ankle dorsiflexors Ankle plantarflexors Balance assessments BBS LOS Reaction time (s) Movement velocity (°/s) Maximal excursion (%) NOTE. Values are mean ⫾ SD. Abbreviation: NA, not applicable.

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Affected

13.9⫾4.5 6.8⫾3.7 14.8⫾4.7 6.1⫾4.1 13.0⫾5.4

Unaffected

Forward

19.0⫾4.7 14.5⫾3.6 21.7⫾5.8 12.8⫾3.7 21.7⫾6.6

Backward

NA

49.1⫾7.1 0.9⫾0.4 2.8⫾1.3 60.3⫾22.1

1.0⫾0.4 4.2⫾2.3 70.3⫾23.1

1.1⫾0.5 2.8⫾1.5 55.9⫾17.9

0.7⫾0.5 1.6⫾1.1 35.6⫾17.3

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Table 4: Intrarater Reliability of 5-Repetition STS Test Scores in Subjects With Stroke Assessor

Mean 5-Repetition STS test score (s)

ICC(3,1) (95% CI)

17.1⫾7.5 16.9⫾7.6

.975 (.935–.992) .976 (.937–.992)

16.9⫾7.6 16.7⫾7.6 17.0⫾7.5

.976 (.939–.992) .971 (.925–.991) .974 (.932–.992)

16.9⫾7.6 16.8⫾7.5 16.8⫾7.5

.970 (.932–.990) .970 (.924–.991) .972 (.929–.991)

Examiner A B Experienced C D E Inexperienced F G H

NOTE. Values are mean ⫾ SD. Abbreviation: CI, confidence interval.

and affected ankle dorsiflexor muscle strength.39 According to the graph, which showed the changes of significant values of correlation coefficients in function of sample size for 1 to 100 correlations,42 the correlation between affected knee extensor (␳⫽–.687) and unaffected ankle dorsiflexor (␳⫽–.629) would approach significant if the sample size were increased to 20 subjects. Besides the small sample recruited, the discrepancy between our findings and other studies may be a result of the differences in the methods used to quantify muscle strength, the testing positions (gravity-assisted or gravity-eliminated positions) adopted during muscle testing, and the characteristics of the subjects with stroke. Relationship of 5-repetition sit-to-stand test with balance measures. No significant correlations were found between 5-repetition STS test scores and BBS in the subjects with stroke in this study. The BBS was a valid measure of standing balance in people with stroke,43 and the lower-limb muscle strength as measured by the 5-repetition STS test was found to contribute 43% of a total variance in BBS in patients with chronic stroke.11 The small sample size recruited might have resulted in the lack of significant correlation between the 5-repetition STS test and BBS. Another possible explanation is the difference in the measurement domains of both tests. While the BBS grades the quality of balance performance, the 5-repetition STS test measures solely the speed (ie, time scores) at which sit-toTable 5: Spearman Correlation Coefficient Between 5-Repetition STS Test and Muscle Strength, BBS and LOS in Subjects With Stroke Parameters

Muscle strength (kg) Hip flexors Knee flexors Knee extensors Ankle dorsiflexors Ankle plantarflexors BBS LOS Reaction time (s) Movement velocity (°/s) Maximal excursion (%)

Affected

Unaffected

Forward

–.587 –.753* –.687 –.007 –.406

–.336 –.830* –.483 –.629 –.510 –.551

.210 –.147 –.084

.210 –.147 –.084

Backward

NA NA NA NA NA

.531 –.480 –.578

Fig 2. ROC curves for 5-repetition STS test scores between (A) young versus healthy elderly (AUCⴝ.816) and (B) healthy elderly versus stroke (AUCⴝ.840). The curved line indicates ROC curve. The straight line indicates nondiscriminating characteristics of the test. Abbreviation: ROC, receiver operating characteristic. –.255 –.179 –.267

Abbreviation: NA, not applicable. *Significant difference after Bonferroni correction at P⬍.05/ 9 (P⬍.00556).

stand maneuvers are performed. In addition, the BBS is known for its ceiling effects,44,45 which may account for the lack of correlation with the 5-repetition STS test. It is surprising to note that no significant correlations were found between the 5-repetition STS test and LOS MXE in the Arch Phys Med Rehabil Vol 91, March 2010

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forward direction in subjects with stroke. In the transition phase of sitting to standing, the initiation of accelerating horizontal momentum occurred, followed by vertical decelerating momentum.46 This motion allowed erect standing to take place from a sitting position. In LOS testing, horizontal movements of the subjects with stroke were examined in terms of their RT, MVL, and MXE. During fast-paced sit-to-stand movement, increased generation of forward momentum16,39 and anteroposterior sway were demonstrated in subjects with stroke.37 The LOS required subjects to possess acceptable visual perceptual capabilities, with a sufficient amount of concentration and attention to track the cursor and move their center of mass toward the designated direction.44 However, the 5-repetition STS test was considerably less challenging because subjects did not need to rely heavily on visual cues or extra concentration to perform the task correctly. The small sample size recruited in this study might also have contributed to the lack of correlation found between the 5-repetition STS test and LOS. Sensitivity of 5-Repetition Sit-to-Stand Test Scores This was the first study to investigate cut-off scores among the young, healthy elderly, and subjects with stroke. We found that our 5-repetition STS test scores were sensitive at discriminating subjects from the 3 groups of the young, healthy elderly, and subjects with stroke with AUC of more than 80%. Moreover, we found a cut-off score of 9.4 seconds between the young and healthy elderly. This is similar to the cut-off score of 10 seconds reported in subjects younger than 60 years.3 It is also interesting to find that the difference between the cut-off scores between the 2 groups (young vs healthy elderly and healthy elderly vs stroke) is only 3 seconds. This might be attributed to the high functional status of our chronic stroke sample. Study Limitations The 5-repetition STS test could assess functional lower-limb muscle strength but could not differentiate specific weakness in each lower limb. The quality of performing the sit-to-stand task might be overlooked because speed is the main focus of the 5-repetition STS test. Our study has several limitations. First, the height of the chair used may not be optimal for all subjects because of variations in the subjects’ leg lengths. Second, factors such as weight-bearing asymmetry47 and foot placement48 were known to influence sit-to-stand performance but were not measured in the present study. Third, our results cannot be generalized to other disease-specific populations because of our subjects’ selection criteria. Fourth, because some of the muscle groups were not tested in gravity-eliminated positions, the effect of gravity might have affected the muscle strength reading obtained. Fifth, our sample size estimation was based on the test-retest reliability of the 5-repetition STS test, which might be not sufficient to detect significant correlation among 5-repetition STS test scores, muscle strength, and balance ability.42 In addition, our study could not establish any causal relationship between variables because of its crosssectional design. Future investigations with larger sample sizes will be essential for prediction and regression analysis as well as establishing the validity of the 5-repetition STS test in subjects with stroke of different mobility levels. CONCLUSIONS The 5-repetition STS test is an easy-to-administer clinical tool, suitable for both experienced and nonexperienced clinicians, with excellent intrarater, interrater, and test-retest reliArch Phys Med Rehabil Vol 91, March 2010

ability. Significant negative correlations with lower-limb muscle strength indicated that the 5-repetition STS test could be used as a functional muscle strength assessment tool in people with stroke. Acknowledgment: statistical advice.

We thank Dr. Raymond C.K. Chung for his

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Arch Phys Med Rehabil Vol 91, March 2010