INTRODUCTION
The ability to rise out of a chair independently is an essential and integral part of safe, daily life performance in older persons.1–3 Community-dwelling older adults, including those with health concerns, stand on average 33 to 71 times a day.4 Lower scores on sit-to-stand measures are predictive of concurrent3 and subsequent5–7 disability, recurrent falls,8 and are correlated with increased risk of mortality.9 The sit-to-stand maneuver is frequently addressed in the rehabilitation of older, medically involved adults.10–13 Measurement tools are necessary to evaluate the effectiveness of interventions employed when treating sit-to-stand deficiencies.
There are several variations of sit-to-stand tests,14–17 including the widely implemented 5-repetition sit-to-stand test (FRSST)16 and the 30-second Chair Stand Test (30 s-CST).18 These tests have been shown to be reliable in a variety of populations.19 Validity studies have demonstrated correlations of the FRSST with knee extension strength,20 static and dynamic balance measures,21 and gait speed.22 The 30 s-CST has shown moderate correlation with body weight–adjusted leg press performance in older adults.18
A common feature of the FRSST and the 30 s-CST is the requirement to stand up without using hand support. Consequently, these tests have decreased practicality for lower-functioning older adult patients who must use hand support to stand. Bohannon23 found that in a sample of home care patients, 57.5% of patients were unable to complete the FRSST, many unable to perform even 1 repetition.23 Similarly, the 30 s-CST was found to have shortcomings in an acutely ill older population. Bodilson et al24 conducted a feasibility study of measures including the 30 s-CST in hospitalized older patients and found that 46% of patients were unable to complete at least 1 repetition without hand support. Kristensen et al25 noted that 81% of patients acutely admitted to a geriatric ward were unable to participate in the 30 s-CST. These findings underscore the need for alternatives for more frail and functionally limited adults in settings such as home care, skilled nursing facilities (SNFs), and hospitals.
The use of the upper extremities (UEs) when rising to stand has been reported to require lower force generation by combined knee extensors.26 Increased success of the sit-to-stand maneuver has also been demonstrated when functionally-impaired older adults use their UEs to rise.27 Significantly improved feasibility and participation have been demonstrated when physically incapacitated older adults are allowed to use UE support during sit-to-stand testing.24,25
A modified 30-second sit-to-stand test (m30STS), which allowed UE use with armrests, was recently introduced and studied in institutionalized older adults.28 Test-retest reliability was reported as good (intraclass correlation coefficient [ICC] = 0.84) and convergent validity with the Timed Up and Go test demonstrated moderate correlation (ICC = −0.62).28 Another novel study of the m30STS demonstrated the ability to significantly account for fall risk in 1 year (falls vs no falls); increased sit-to-stands were associated with fewer falls.29 These recent studies show promise in accommodating the physiologic constraints of more frail adults with a modified measurement tool.
As outcome measures should demonstrate reliability between raters, the first purpose of this study was to examine interrater and test-retest intrarater reliability for the m30STS for individuals 65 years of age and older. These types of reliability have not yet been investigated for the m30STS. Our second purpose was to examine validity by investigating the relationship between the m30STS and balance, lower leg strength to body weight ratio, and activities of daily living measures in older adults undergoing rehabilitation. These measures have demonstrated correlation with other sit-to-stand tests.18,20,22,30,31 This is the first study the authors are aware of to investigate convergent and predictive validity of the m30STS with these measures. For our third purpose, we sought to study the responsiveness of the m30STS to change in a physically challenged older population and calculate minimal detectable change (MDC90) values for more accurate interpretation of scoring.
METHODS
Study Design and Participants
The Arcadia University Committee for the Protection of Research Subjects approved this study. All participants, including raters, signed an informed consent form before engaging in the study and received written information about the project.
This research was conducted in 2 phases. The first phase was an intra- and interrater reliability study, which included participants who were filmed performing the m30STS and raters who scored the filmed tests. A convenience sample of 7 participants was recruited from 2 assisted living facilities Aegis Lodge and Madison House and the outpatient caseload of an SNF (Life Care Center of Kirkland) in May of 2017. Participants were considered eligible if they were 65 years of age or older and unable to stand up at least once from a standard height chair (45-48 cm) without UE support. Exclusion criteria consisted of (1) any physician order for restriction in weight bearing of the lower extremities or UEs, (2) posterior hip precautions or other precautions limiting degree of hip flexion, (3) inability to understand verbal instructions, (4) inability to understand or sign the consent agreement, (5) inability to cooperate because of behavior disturbance, (6) inability to understand English, (7) diagnosis of dementia, and (8) pain in the hip, knee, ankle, or spine exacerbated by 1 repetition of the sit-to-stand movement. Participants were on average 85.0 (9.2) years of age, had 2.0 (1.0) primary diagnoses for which they were being seen by physical therapist, and had 7.0 (1.9) comorbidities listed in their medical history. Participants were not selected or excluded on the basis of specific diagnoses to create a representative sample of lower-functioning older adults in a rehabilitation setting. Participants were filmed in a single session performing the m30STS. The primary investigator administered the test.
Ten raters were recruited from the staff of the SNF research site. All physical therapists and physical therapist assistants on staff at the SNF were eligible. Six raters were physical therapists and 4 were physical therapist assistants. The physical therapists and physical therapist assistants had a median of 11 years (range: 1-18 years) of experience in geriatric practice. Both physical therapists and physical therapist assistants were included on the basis of the study location's state practice act, which allows physical therapist assistants to administer functional tests. In states with similar practice acts, it is a common practice for physical therapist assistants to routinely score functional tests.
The raters attended a training session on the m30STS, which was conducted by the primary investigator. In a separate session, the raters viewed the filmed tests of the 7 participants and scored each participant. Twenty-one days later, the raters viewed the same tests and scored each participant as in the previous session. All therapists completed the 2 viewing sessions within a 21- to 25-day time frame; the primary investigator proctored all scoring sessions.
Sample size was calculated for the reliability analysis on the basis of 2 ratings for intrarater reliability having 2 observations, a target ICC of 0.80 and 80% power.32 Under these assumptions, a sample size of 7 was determined to be necessary. Because 10 observers were used for interrater reliability, with the expected ICC of 0.80, and 80% power, only 3 participants would be needed.32 All 7 participants' data were used for both intra- and interrater reliability.
The second phase sought to determine validity and minimal detectable change (MDC). All individuals 65 years of age and older admitted to inpatient or outpatient physical therapy of the SNF research site (Life Care Center of Kirkland) were screened for eligibility. Inclusion and exclusion criteria were identical to that of the participants in phase 1. Screening of all therapy admissions was conducted for 90 days from June through August of 2017; 149 individuals were screened and 33 met the inclusion criteria. Participants were on average 85.2 (8.0) years of age and had on average 2 (1.3) primary diagnoses and 5.2 (1.8) comorbidities listed in their medical history. Participants had a median time from admit to discharge of 15.0 days (range: 3-161 days). Sample size for the validity analysis was calculated using the assumption of an estimated Spearman ρ of 0.50, an α of .05, and 80% power.33 The sample calculated indicated that 29 participants should be enrolled; 33 total participants were enrolled by the conclusion of the study.
Physical therapists and physical therapist assistants employed by the SNF research site served as research project assistants. Their primary role was administering the tests for data collection. They occasionally assisted with the screening and consent process if the primary investigator was not available due to logistical constraints. Prior to the start of the project, all project assistants attended a training session conducted by the primary investigator. Training included a description of the study, inclusion/exclusion criteria, process for participant education and consent, and the testing procedures to standardize implementation. A total of 6 physical therapists and 6 physical therapist assistants participated as project assistants. The physical therapists and physical therapist assistants had a median of 9 years (range: 1-18 years) of experience in geriatric practice. Participants were tested by the project assistants at the initial physical therapy examination with the Berg Balance Scale, the m30STS, and bilateral knee extensor strength measured by handheld dynamometry. Knee extension strength to body weight ratio was selected as strength measure because it has been previously reported to be associated with sit-to-stand performance26 and testing.20
If the tests could not be completed at the initial examination because of time constraints or fatigue, they were completed within 48 hours at subsequent therapy sessions. The tests were repeated within 48 hours of planned discharge from physical therapy. Scores for the modified Barthel Index34 were collected from the patient's chart and scored within the described time frame. The modified Barthel Index retains the 10 items of the original Barthel Index with a modified scoring system to increase sensitivity to detecting change.34 The modified Barthel Index was routinely administered at the SNF research site by occupational therapists and certified occupational therapist assistants. The scoring of the test was included in routine orientation of occupational therapists and certified occupational therapist assistants upon employment at the SNF research site.
Testing Procedures
To standardize the testing procedure, the m30STS was administered with the following protocol. Participants were screened prior to testing for inclusion and exclusion criteria. Two chairs with a seat height of 45.7 cm (18 in) and standard armrests were designated to be used in the study. One was located in the inpatient area and a second located in the outpatient clinic. If the participant could not access the designated chair because of obesity or other concerns regarding participant comfort, a wheelchair was substituted using the discretion of the evaluating therapist. All substitutions were noted on the data collection sheet. The chair was placed against the wall to prevent it from moving. The test began with the participant seated in the middle of the chair, with his or her back straight, and feet shoulder width apart. The participant was instructed to place his or her hands on the armrests. At the signal “go,” the participant rose to a full stand with the body straight and erect and then returned to the initial position. The participant was not permitted to lean back on the chair with his or her legs. The participant could use UE support as necessary to rise to stand; however, the participant was instructed to let go of the armrests and bring the UEs to the midline of the body when attaining a fully upright standing posture. The use of a walker or other device for balance upon standing was not permitted. The participant was instructed to fully sit down between each stand and to stop if the sit-to-stand movement exacerbated pain. The number of stands a participant performed in 30 seconds was counted and recorded. If the participant stood more than halfway at the end of the timing, it was counted as a stand. The participant was allowed 1 to 2 practice rises in order to clarify correct technique if needed prior to the test.
Knee extensor strength testing was performed with a microFET2 digital handheld dynamometer (Hoggan Scientific, LLC, Salt Lake City, Utah), which was routinely used in practice by therapists in the research site. The dynamometer was calibrated 1 month prior to the study. The testing position and method were based on methods previously described.35,36 The participant was seated upright, with the knees in 90° flexion. A raised mat was used in cases in which a chair was insufficient to allow for free movement of the leg into 90° flexion. A block for stabilization of the opposite foot was used if participant comfort dictated it. Participants were instructed to sit upright and avoid leaning back in the chair or on the mat during testing. Participants were permitted to use the UEs for support on the chair or the mat. The dynamometer was placed perpendicular to and just proximal to the malleoli on the lower leg. Participants were instructed to take 1 to 2 seconds to come to maximum effort and were given encouragement to push into knee extension as hard as they were able into the dynamometer for approximately 7 seconds. The tester provided counterforce, with no additional force added. The dynamometer was not allowed to move, in order to resist the force generated by the participant. Two trials were permitted and peak force was recorded. The larger of the 2 trials was used.
The Berg Balance Scale was administered per guidelines that have previously been defined.37 Phase II of the study also sought to establish responsiveness to change of the m30STS via the MDC.
Data Analysis
Data were analyzed using IBM SPSS for Mac (version 23.0; IBM Corp, Armonk, New York). Descriptive statistics were calculated for demographic and testing variables. Interclass correlation coefficients were calculated to determine the reliability coefficients for phase I. Spearman correlations were calculated to establish concurrent and predictive validity for phase II. Linear and ordinal regressions were performed on significant correlations to establish predictive validity. For phase III, the standard error of the measure (SEM) and MDC90 were calculated.
To calculate the MDC, the SEM was first calculated using the equation SEM = SD × √1 − r, in which the standard deviation of the m30STS was used from the 33 participants in phase II. The reliability coefficient used was the intrarater reliability ICC of the measure established in phase I. The MDC was then calculated using the formula for the MDC at the 90% confidence interval which is MDC90 = SEM × 1.65 × √2.38 The SEM used was from the first calculation, 1.65 is the z score at the 90% confidence level from a normal distribution, and √2 adjusts for errors associated with the repeated measures associated with test-retest intrarater reliability.
RESULTS
Reliability
Interrater reliability using absolute agreement was calculated as ICC2,1 = 0.737 (P ≤ .001). Test-retest intrarater reliability using absolute agreement was calculated as ICC2,k = 0.987 (P ≤ .001).
Validity
The initial m30STS correlates with the initial Berg Balance Scale (Spearman ρ = 0.737, P = .01) and the initial modified Barthel Index (Spearman ρ = 0.711, P = .01), as well as individual subscale items on the modified Barthel Index bathing (Spearman ρ = 0.511, P = .01), toileting (Spearman ρ = 0.581, P = .01), stair climbing (Spearman ρ = 0.566 P = .01), ambulation (Spearman ρ = 0.653, P = .01), and transfers (Spearman ρ = 0.574, P = .01). Only one participant used a wheelchair, thus concurrent validity was not computed for wheelchair mobility on the modified Barthel Index. There were no correlations between initial strength to body weight ratio and the m30STS (Spearman ρ range = 0.108-0.282, P ≥ .05), nor were there correlations between the unadjusted initial strength values and m30STS (Spearman ρ range = 0.121-0.251, P ≥ .05). (See the Table for descriptive statistics of all variables.)
Table. -
Descriptive Statistics of Phase II Measures
|
Initial |
Discharge |
| Mean |
SD |
Mean |
SD |
| Berg Balance Scale |
22.2 |
13.6 |
33.8 |
10.5 |
| m30STS |
2.8 |
2.7 |
4.8 |
5.5 |
| Left knee extensors handheld dynamometry, lbf |
29.3 |
9.9 |
34.6 |
11.7 |
| Right knee extensors handheld dynamometry, lbf |
31.5 |
14.7 |
36.1 |
13.4 |
|
Median
|
Range
|
Median
|
Range
|
| Barthel bathing score |
3.0 |
0-5.0 |
4.0 |
1.0-5.0 |
| Barthel toilet score |
5.0 |
0-10.0 |
9.0 |
5.0-10.0 |
| Barthel stair score |
0 |
0-8.0 |
2.0 |
0-10.0 |
| Barthel ambulation score |
8.0 |
0-15.0 |
8.0 |
8.0-15.0 |
| Barthel transfer score |
8.0 |
3.0-15.0 |
15.0 |
8.0-15.0 |
Abbreviation: m30STS, modified 30-second sit-to-stand test.
The discharge m30STS showed a similar pattern of correlation to other discharge measures as the initial concurrent validity metrics. The discharge m30STS correlated with the discharge Berg Balance Scale (Spearman ρ = 0.727, P = .01), the discharge modified Barthel Index (Spearman ρ = 0.824, P = .01), and discharge modified Barthel Index subscales of Bathing (Spearman ρ = 0.429, P = .05), Toileting (Spearman ρ = 0.447, P = .05), Ambulation (Spearman ρ = 0.539, P = .01), and Transferring (Spearman ρ = 0.446, P = .05). There were no correlations between discharge strength to body weight ratio and the m30STS (Spearman ρ range = 0.153-0.322, P ≥ .05), nor were there correlations between the unadjusted discharge strength values and m30STS (Spearman ρ range = 0.110-0.115, P ≥ .05). (See the Table for descriptive statistics of all variables.)
The initial m30STS correlated with the discharge Berg Balance Scale (Spearman ρ = 0.578, P = .01), the discharge modified Barthel bathing score (Spearman ρ = 0.498, P = .010), and the discharge modified Barthel ambulation score (Spearman ρ = 0.504, P = .009). However, the initial m30STS did not correlate with the discharge modified Barthel Index (Spearman ρ = 0.375, P = .059), the discharge modified Barthel subscales of toilet score (Spearman ρ = 0.375, P = .059) or discharge stair score (Spearman ρ = 0.285, P = .167) or the total time of care (Spearman ρ = −0.336, P = .056).
For linear regression analysis, the ability of the initial m30STS to predict discharge Berg Balance Scale yielded the significant regression equation of discharge Berg Balance Scale = 2.119 (m30STS) + 27.970 (P ≤ .001). The adjusted R2 of this model is 0.315, indicating that the initial m30STS predicts 31.5% of the variability in the discharge Berg Balance Scale. Entering the initial m30STS into ordinal regressions to predict the discharge modified Barthel Index bathing scores and ambulation scores did not yield significant results (P = .108 and .108, respectively).
Minimal Detectable Change
The SEM was calculated using the standard deviation of 2.70 taken from the initial m30STS standard deviation and the test-retest intrarater reliability coefficient of 0.987. The SEM was calculated to be 0.30. The MDC90 was calculated to be 0.70.
DISCUSSION
To the best of our knowledge, this is the first investigation of the interrater and test-retest intrarater reliability of the m30STS. Our study found that ICC2,1 of 0.737 for interrater reliability and ICC2,k of 0.987 for test-retest intrarater reliability establish moderate and excellent reliability, respectively.39
The m30STS demonstrated moderate concurrent validity with the Berg Balance Scale and moderate to good concurrent validity with the total scores of the modified Barthel Index. Concurrent validity of the m30STS with these measures has not been previously reported in the literature.40 The Berg Balance Scale is a well-established clinical balance measure with good psychometric properties.41 We defined a testing procedure for the m30STS, which had relatively high balance demands. The participant was not allowed to lean back on the chair with the lower extremities and had to let go of the armrests with each repetition, moving the UEs toward the midline of the body; the use of an assistive device was not allowed. Concurrent validity findings with the Berg Balance Scale in this study illustrate that the m30STS captures an aspect of balance capacity. In addition, the m30STS demonstrated moderate predictive validity for higher Berg Balance Scale scores at discharge.40 Higher repetitions initially performed on m30STS were predictive of higher BBS scores at discharge, explaining 31.5%, or approximately one-third of the variability in the balance score. The current and predictive validity findings are unsurprising, given the higher balance demands of the m30STS. The modified Barthel Index is a widely used measure of functional performance and accepted as a valid tool.42 The fact that the modified Barthel Index correlated with the m30STS lends weight to the m30STS as a clinically relevant tool that reflects improvements in functional performance.
The m30STS did not correlate with knee extensor strength to body weight ratio. The use of the UEs on armrests to rise to stand has demonstrated an approximate 50% reduction of the mean maximum hip moment and 30% reduction of the mean knee moment.43 The addition of UE support in the m30STS may have decreased the relative contribution of lower leg strength to such a degree that a significant correlation of LE strength with the m30STS was negated.
In comparison with other sit-to-stand tests, the m30STS demonstrated increased feasibility in the geriatric population. Of 33 participants who were tested on initial examination in phase II of this study, 24 participants (73%) were able to perform at least 1 repetition of standing in the test. The percentage of participants able to perform 1 repetition was higher at discharge: 82% of participants (22 participants of 27 total) were able to perform at least 1 repetition.
The MDC90 of 0.70 established in this study means that an increase of 1 additional repetition in the m30STS is a change beyond error. This provides an essential piece of information for the clinician looking to establish whether progress can be considered a real change.
A possible limiting factor in our study of interrater reliability may have been the challenge of interpreting from the film if the participant was indeed balancing independently without leaning back on the chair. This element may be more easily judged in live testing and may yield higher interrater reliability in clinical practice. Nevertheless, our findings indicate that the m30STS is a reliable tool in a geriatric population with a lower level of function.
Another potentially limiting factor in our study of validity was the collection of the modified Barthel Index scores from chart review. This may have contributed unaccounted variability in the scoring of this measure.
The participants in phase II were associated with 1 SNF and may not be representative of all lower-functioning older adults. The sample for phase I was selected by convenience from the associations at the primary investigator's practice setting and also may not be typical of the older adult population at large. The isometric strength testing of the knee extensors represented only 1 muscle group active in the sit-to-stand maneuver. Future studies should assess possible correlations between the m30STS and more global strength measures.
CONCLUSIONS
The m30CST is a reliable, feasible tool for use in a general geriatric population with a lower level of function. The m30STS demonstrated concurrent validity with the Berg Balance Scale and modified Barthel Index but not with knee extensor strength to body weight ratio. One repetition of the m30STS was established as the MDC90 as change beyond error. These findings strengthen the psychometric properties of the m30STS as an outcome measure for clinical use.
ACKNOWLEDGMENTS
The authors thank the physical therapy and occupational therapy staff at Life Care Center of Kirkland for the testing of participants and assisting with the consent process.
REFERENCES
1. Rikli RE, Jones CJ. Development and validation of criterion-referenced clinically relevant fitness standards for maintaining physical independence in later years. Gerontologist. 2013;53(2):255–267.
2. Gama ZA, Gomex-Conesa A. Risk factors for falls in the elderly: systemic review. Rev Saude Publica. 2008;42(5):946–956.
3. den Ouden ME, Schururmans MJ, Arts IE, van der Schouw YT.
Physical performance characteristics related to disability in older persons: a systematic review. Maturitas. 2011;69(3):208–219.
4. Bohannon RW. Daily sit-to-stands performed by adults: a systematic review. J Phys Ther Sci. 2015;27(3):939–942.
5. Guralnik JM, Ferrucci L, Simonsick EM, Salive ME, Wallace RB. Lower-extremity function in persons over the age of 70 years as a predictor of subsequent disability. N Engl J Med. 1995;332(9):556–561.
6. Huang WW, Perera S, VanSwearingen J, Studenski S. Performance measures predict the onset of basic ADL difficulty in community-dwelling older adults. J Am Geriatr Soc. 2010;58(5):844–852.
7. Zhang F, Ferrucci L, Culham E, Metter EJ, Guralnik J, Deshpande N. Performance on Five Times Sit to Stand task as a predictor of subsequent falls and disability in older persons. J Aging Health. 2013;25(3):478–492.
8. Buatois S, Miljkovic D, Manckoundia P, et al. Five Times Sit to Stand test is a predictor of recurrent falls in healthy community-living subjects aged 65 and older. J Am Geriatr Soc. 2008;56(8):1575–1577.
9. Cooper R, Kuh D, Hardy R Mortality Review Group; FALCon and HALCyon Study Teams. Objectively measured physical capability levels and mortality: systematic review and meta-analysis. BMJ. 2010;341:c4467.
10. Mun B, Lee Y, Kim T, et al. Study on the usefulness of sit to stand training in self-directed treatment of stroke patients. J Phys Ther Sci. 2014;26(4):483–485.
11. Toots A, Littbrand H, Lindelof N, et al. Effects of a high-intensity functional exercise program on dependence in activities of daily living and balance in older adults with dementia. J Am Geriatr Soc. 2016;64(1):55–64.
12. Boyne P, Israel S, Dunning K. Speed-dependent body weight supported sit-to-stand training in chronic stroke: a case series. J Neurol Phys Ther. 2011;35(4):178–184.
13. Britton E, Harris N, Turton A. An exploratory randomized controlled trial of assisted practice for improving sit-to-stand in stroke patients in the hospital setting. Clin Rehabil. 2008;22(5):458–468.
14. Bohannon RW. Sit-to-stand test for measuring performance of lower extremity muscles. Percept Mot Skills. 1995;80(1):163–166.
15. Csuka M, McCarty D. Simple method for measurement of lower extremity strength. Am J Med. 1985;78(1):77–81.
16. Bohannon RW. Five-repetition sit-to-stand test performance by community-dwelling adults: a preliminary investigation of times, determinants, and relationship with self-reported
physical performance. Isokin Ex Sci. 2007;15(2):77–81.
17. Bohannon RW. Measurement of sit-to-stand among older adults. Top Geriatr Rehabil. 2012;28(1):11–16.
18. Jones CJ, Rikli RE, Beam WC. A 30-second chair stand test as a measure of lower body strength in community-residing older adults. Res Q Exerc Sport. 1999;70(2):113–119.
19. Bohannon RW. Test-retest
reliability of the five-repetition sit-to-stand test: a systematic review of the literature involving adults. J Strength Cond Res. 2011;25(11):3205–3207.
20. Bohannon RW. Sit-to-stand test: performance and determinants across the age-span. Isokinet Exerc Sci. 2010;18(4):235–240.
21. Goldberg A, Chavis M, Watkins J, Wilson T. The Five Times Sit to Stand test:
validity,
reliability, and detectable change in older females. Aging Clin Exp Res. 2012;24(4):339–344.
22. Schaubert KL, Bohannon RW.
Reliability and
validity of three strength measures obtained from community-dwelling elderly persons. J Strength Cond Res. 2005;19(3):717–720.
23. Bohannon RW. Five-repetition sit-to-stand test: usefulness for older patients in a home-care setting. Percept Mot Skills. 2011;112(3):803–806.
24. Bodilson AC, Juul-Larsen HG, Peterson J, Beyer N, Andersen O, Bandholm T. Feasibility and inter-rater
reliability of
physical performance measures in acutely admitted older medical patients. PLoS One. 2015;10(2): e0118248.
25. Kristensen MT, Jakobsen TL, Nielson JW, Jørgensen LM, Nienhuis RJ, Jønsson LR. Cumulated ambulation score to evaluate mobility is feasible in geriatric patients and in patients with hip fracture. Dan Med J. 2012;59(7):A4464.
26. Eriksrud O, Bohannon RW. Relationship of knee extension force to independence in sit-to-stand performance in patients receiving acute rehabilitation. Phys Ther. 2003;83(6):544–551.
27. Alexander NB, Galecki AT, Nyquist LV. Chair and bed rise performance in ADL-impaired congregate housing residents. J Am Geriatr Soc. 2000;48(5):526–533.
28. Le Berre M, Apap D, Babcock J, et al. The psychometric properties of a modified Sit-to-Stand Test with use of the upper extremities in institutionalized older adults. Percep Mot Skills. 2016;123(1):138–152.
29. Applebaum EV, Breton D, Feng ZW, et al. Modified 30-second Sit to Stand Test predicts falls in a cohort of institutionalized older veterans. PLoS One. 2017;12(5):e0176946.
30. Whitney SL, Wrisely DM, Marchetti GF, Gee MA, Redfern MS, Furman JM. Clinical measurement of sit-to-stand performance in people with balance disorders:
validity of data for the Five Times Sit to Stand test. Phys Ther. 2005;85(10):1034–1045.
31. Lord SR, Murray SM, Chapman K, Munro B, Tiedemann A. Sit-to-stand performance depends on sensation, speed, balance and psychological status in addition to strength in older people. J Gerontol A Biol Med Sci. 2002;57(8):M539–M543.
32. Bujang M, Baharum N. A simplified guide to determination of sample size requirements for estimating the value of intraclass correlation coefficient: a review. Arch Orofac Sci. 2017;12(1):1–11.
33. Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing Clinical Research: An Epidemiologic Approach. 4th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2013. Appendix 6C, page 79.
34. Shah S, Vanclay F, Cooper B. Improving the sensitivity of the Barthel Index for stroke rehabilitation. J Clin Epidemiol. 1989;42(8):703–709.
35. Bohannon RW. Test-retest
reliability of hand-held dynamometry during a single session of strength assessment. Phys Ther. 1986;66(2):206–208.
36. Mentiplay BF, Perraton LG, Bower KJ, et al. Assessment of lower limb muscle strength and power using hand-held and fixed dynamometry: a
reliability and
validity study. PLoS One. 2015;10(10):e0140822.
37. Berg K, Wood-Dauphinee S, Williams JI, Gayton D. Measuring balance in the elderly: preliminary development of an instrument. Physiother Canada. 1989;41(6):304–311.
38. Haley SM, Fragala-Pinkham MA. Interpreting change scores of tests used in physical therapy. Phys Ther. 2006;86(5):735–743.
39. Koo TK, Li MY. A guideline of selecting and reporting interclass correlation coefficients for
reliability research. J Chiropr Med. 2016;15(2):155–163.
40. Zou KH, Tuncali K, Silverman SG. Correlation and simple linear regression. Radiology. 2003;227(3):617–628.
41. Sibley KM, Howe T, Lamb SE, et al. Recommendations for a core outcome: set for measuring standing balance in adult populations: a consensus-based approach. PLoS One. 2015;10(3):e0120568. eCollection 2015.
42. Quinn TJ, Langhorne P, Stott D. Barthel Index for stroke trials: development, properties, and application. Stroke. 2011;42(4):1146–1151.
43. Arborelius UP, Wrentenberg P, Lindberg F. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics. 1992;35(11):1377–1391.
