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A Scoping Review of Physical Performance Outcome Measures Used in Exercise Interventions for Older Adults With Alzheimer Disease and Related Dementias

McGough, Ellen L., PT, PhD1; Lin, Shih-Yin, MM-BC, MPH, PhD2; Belza, Basia, RN, PhD2,3; Becofsky, Katie M., PhD4; Jones, Dina L., PT, PhD5; Liu, Minhui, RN, PhD2,6; Wilcox, Sara, PhD7; Logsdon, Rebecca G., PhD2,3

Journal of Geriatric Physical Therapy: January/March 2019 - Volume 42 - Issue 1 - p 28–47
doi: 10.1519/JPT.0000000000000159
Systematic Reviews

Background and Purpose: There is growing evidence that exercise interventions can mitigate functional decline and reduce fall risk in older adults with Alzheimer disease and related dementias (ADRD). Although physical performance outcome measures have been successfully used in older adults without cognitive impairment, additional research is needed regarding their use with individuals who have ADRD, and who may have difficulty following instructions regarding performance of these measures. The purpose of this scoping review was to identify commonly used physical performance outcome measures, for exercise interventions, that are responsive and reliable in older adults with ADRD. Ultimately, we aimed to provide recommendations regarding the use of outcome measures for individuals with ADRD across several domains of physical performance.

Methods: A scoping review was conducted to broadly assess physical performance outcome measures used in exercise interventions for older adults with ADRD. Exercise intervention studies that included at least 1 measure of physical performance were included. All physical performance outcome measures were abstracted, coded, and categorized into 5 domains of physical performance: fitness, functional mobility, gait, balance, and strength. Criteria for recommendations were based on (1) the frequency of use, (2) responsiveness, and (3) reliability. Frequency was determined by the number of studies that used the outcome measure per physical performance domain. Responsiveness was assessed via calculated effect size of the outcome measures across studies within physical performance domains. Reliability was evaluated via published studies of psychometric properties.

Results and Discussion: A total of 20 physical performance outcome measures were extracted from 48 articles that met study inclusion criteria. The most frequently used outcome measures were the 6-minute walk test, Timed Up and Go, repeated chair stand tests, short-distance gait speed, the Berg Balance Scale, and isometric strength measures. These outcome measures demonstrated a small, medium, or large effect in at least 50% of the exercise intervention studies. Good to excellent reliability was reported in samples of older adults with mild to moderate dementia. Fitness, functional mobility, gait, balance, and strength represent important domains of physical performance for older adults. The 6-minute walk test, Timed Up and Go, repeated chair stand tests, short-distance gait speed, Berg Balance Scale, and isometric strength are recommended as commonly used and reliable physical performance outcome measures for exercise interventions in older adults with mild to moderate ADRD. Further research is needed on optimal measures for individuals with severe ADRD.

Conclusions: The results of this review will aid clinicians and researchers in selecting reliable measures to evaluate physical performance outcomes in response to exercise interventions in older adults with ADRD.

1Department of Rehabilitation Medicine, University of Washington, Seattle, Washington.

2School of Nursing, University of Washington, Seattle, Washington.

3Health Promotion Research Center, University of Washington, Seattle, Washington.

4Department of Kinesiology, University of Massachusetts Amherst, Amherst, Massachusetts.

5Department of Orthopaedics, Division of Physical Therapy, and Injury Control Research Center, West Virginia University, Morgantown, West Virginia.

6Center for Innovative Care in Aging School of Nursing, Johns Hopkins University, Baltimore, Maryland.

7Department of Exercise Science and Prevention Research Center, University of South Columbia, South Carolina.

Address Correspondence to: Ellen L. McGough, PT, PhD, Department of Rehabilitation Medicine, University of Washington, 1959 NE Pacific St, Box 356490, Seattle, WA 98195 (emcg@uw.edu).

This publication was supported (in part) by the Healthy Brain Research Network (HBRN) funded by the CDC's Alzheimer's Disease and Healthy Aging Program. The HBRN is a thematic network of CDC's Prevention Research Centers Program. Efforts were supported in part by cooperative agreements: U48 DP 005000 and U48 DP005013.

The findings and/or conclusions of this publication are those of the authors and do not necessarily represent the official views of the Centers for Disease Control and Prevention.

The authors declare no conflicts of interest.

Robert Wellmon was the Decision Editor.

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INTRODUCTION

Alzheimer disease and related dementias (ADRD) are complex neurocognitive disorders characterized by progressive memory loss and declining language, attention, executive function, perceptual-motor skills, and social cognition.1 In addition to these neurocognitive changes, alterations in sensory and motor systems affect physical and functional status.2 Notably, changes in physical performance often precede the onset of dementia, and physical function progressively declines with advancing stages of disease.3 There is evidence to support the use of exercise interventions for individuals with ADRD to mitigate physical decline, prevent falls, and preserve day-to-day function.4 , 5 However, determining the effectiveness of exercise interventions in this population is challenging, as many tests of physical health and functional status require a high level of comprehension, memory, and attention for an individual to perform to the best of their ability. Thus, outcome measures used commonly with older adults without ADRD may not translate for use in individuals with these conditions.

The purpose of this article was to identify commonly used physical performance outcome measures that are responsive and reliable in older adults with ADRD. This scoping review of the literature provides a review of physical performance measures in people with ADRD through May 2015 and is specific to physical performance outcomes of exercise interventions. This review differs from a review completed by Bossers et al6 in that it is focused exclusively on exercise interventions, includes a larger variety of study designs, and compares effect sizes for measures across multiple studies. Scoping reviews are useful in areas in which researchers are unable to perform systematic reviews because of fewer studies that use rigorous designs, such as randomized controlled trials.7–9 To our knowledge, no scoping reviews have been conducted to date on physical performance outcome measures for use in exercise interventions for older adults with ADRD. Since we aimed to develop a comprehensive inventory of potential physical performance outcome measures for individuals with ADRD, it was appropriate to include a greater variety of research designs (eg, quasiexperimental studies) to ensure the completeness of the review. For this investigation, exercise was defined as physical activity that is planned, structured, and repetitive over an extended period, with the purpose to improve fitness, performance, or health.10 Physical performance outcome measures were evaluated on 3 criteria: frequency of use, responsiveness, and reliability in studies of older adults with ADRD.

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METHODS

Search Strategies

The strategy outlined in Appendix A was used to search for studies published between January 2000 and May 2015 first using PubMed, and then replicated in CINAHL, PsycINFO, Embase, and ALOIS.

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Inclusion and Exclusion Criteria

Studies were included if they met the following criteria: (1) were published in English between January 2000 and May 2015; (2) sampled predominantly older adults (65 years and older); (3) included at least 20 participants with ADRD, including mild cognitive impairment (MCI) or dementia indicated by a clinical diagnosis and/or cognitive testing; (4) included an exercise intervention; and (5) reported at least 1 outcome measure related to objective physical functioning. Studies were excluded if participants had neurological conditions other than ADRD (eg, Parkinson's disease, stroke, traumatic brain injury, Huntington's disease, and HIV-induced dementia) or if the outcome measures were unique to a single study and psychometric data were not available for individuals with ADRD.

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Selection of Articles and Data Extraction

The study flowchart is shown in Figure 1. Two reviewers (S.L. and R.L.) independently screened the title of all entries (N = 2938) yielded from the 5 electronic databases and then met to resolve disagreements. When the relevancy of an article could not be determined by its title, the 2 reviewers consulted its abstract. After the 2 reviewers resolved all disagreements, the abstracts of all relevant entries (N = 362) were equally distributed to 4 pairs of reviewers. All reviewers were researchers with experience in conducting systematic and/or scoping reviews or who had research expertise in ADRD, exercise, physical activity, and/or physical performance outcomes. Each reviewer of the pair first reviewed all of the assigned abstracts against the aforementioned inclusion/exclusion criteria independently, and then the 2 reviewers met to resolve disagreements. After each pair had reached consensus on relevancy of abstracts, the full articles of these abstracts (N = 116) were redistributed to the 4 pairs of reviewers for further review and data abstraction. Each reviewer independently extracted information from the assigned full articles on study design, sample size, type of cognitive impairment, intervention characteristics, and outcome measures, and entered these data into an online abstraction tool. Following independent review, each pair of reviewers again compared their results, resolved any disagreements, and consolidated their data extraction forms. In rare cases where pairs of reviewers did not reach consensus, articles were discussed among the entire team and questions were resolved. The reference list of each full article was also reviewed during the data abstraction process to identify additional relevant articles. Scores on the Mini-Mental State Examination were extracted from each study to describe the level of cognitive impairment of study participants. The Mini-Mental State Examination scale ranges from 0 to 30: mild dementia = 21 to 25, moderate dementia = 11 to 20, and severe dementia = 0 to 10.11

Figure 1

Figure 1

All outcome measures identified and coded in the abstraction process were categorized into 5 domains of physical performance (Figure 2): fitness, functional mobility, gait, balance, and strength.12–14 These domains were selected based on their important role in the everyday function of older adults as defined by the NIH Toolbox, the American College of Sports Medicine, and other resources.13 , 14 Although constructs of physical performance domains are closely related, they are distinct in their physiological and functional response to specific exercise interventions.11 Fitness (endurance), gait (locomotion), balance, and strength have been identified as distinct constructs of motor function, while functional mobility results from combinations of movement.9 , 13

Figure 2

Figure 2

Once the outcome measures were abstracted and categorized into domains, we abstracted the means and standard deviations from each study to calculate effect sizes, our indicator of responsiveness. Finally, to evaluate reliability, we retrieved psychometric studies and reviewed them for test-retest reliability and interrater reliability in older adults with ADRD.

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Statistical Analysis

One of the authors (S.L.) computed Cohen's d effect sizes (ESs) for each identified outcome measure in each study using the Stata 13 software (StataCorp, LP) to examine the magnitude of change in response to an exercise intervention. To ensure a consistent basis of comparison, ESs were only calculated when both pretest and posttest means and standard deviations were available (See Appendix B for formulas). The magnitude of the ES was defined according to the guidelines proposed by Cohen15 and Sawilowsky,16 d = 0.20 small, d = 0.50 medium, and d = 0.80 large. An ES less than 0.20 was considered to reflect an intervention that had minimal to no effect. The frequency of an outcome measure for each domain was reported.

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RESULTS

Our final sample included 48 articles; 2 of which described different outcomes from the same study.17 , 18 A total of 20 outcome measures were extracted and organized into the physical performance domains of fitness (3 measures), functional mobility (6 measures), gait (3 measures), balance (6 measures), and strength (2 measures).

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Fitness Measures

Studies that measured fitness are summarized in Table 1. The 6-minute walk test (6MWT) 19 was used as an outcome in 8 studies, comprising 5 randomized controlled trials (RCTs), 2 nonrandomized trials (NRTs), and 1 single-group pre-post study. In the 6MWT, the participant is asked to walk as far as possible, in 6 minutes, on a flat, indoor corridor (30-m length preferred) with turnaround points marked by a cone. Among the 5 RCTs, the 6MWT demonstrated a large ES in 1 study (d = 2.9),20 small ESs (d = 0.20-0.46) in 3 RCTs,21–23 and no meaningful ES in 1 RCT.24 Medium to large ESs (d = 0.67-1.69) were demonstrated in the NRTs.25 , 26 A large ES was also observed in the pre-post study (d = 0.81).27 The 6MWT has demonstrated good to excellent relative test-retest reliability in studies of older adults with mild to moderate dementia (intraclass correlation coefficient [ICC] = 0.86; n = 58)28 and mild to severe dementia (ICC = 0.98-0.99; n = 51).29

Table 1

Table 1

The 2-minute walk test (2MWT) 19 was used as an outcome measure in 1 RCT30 and 1 NRT.31 In the 2MWT, the participant is asked to walk as far as possible, in 2 minutes, on a flat, indoor corridor (30-m length preferred), with turnaround points marked by a cone.32 No effect was seen in the RCT, but a small ES was demonstrated in the NRT (d = 0.21). Reliability of the 2MWT has not been reported in people with ADRD. The 2MWT has demonstrated concurrent validity with the 6MWT in older adults without dementia living in long-term care (r = 0.92).33 Two studies used the 2-minute step test from the Senior Fitness Test.34 One was an NRT, yielding a large ES (d = 0.89);35 the other was a time series study, yielding minimal to no effect (d = 0.18).36 No studies were identified examining the psychometric properties of the 2-minute step test in people with ADRD.

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Functional Mobility Measures

Studies that measured functional mobility are summarized in Table 2. A repeated chair stand test, including the 30-second chair stand (and modified 10-second) and 5-time sit-to-stand (FTSTS), was used in 20 of 47 studies to measure functional mobility and lower extremity strength. The 30-second chair stand test measures the maximum number of times the participant is able to stand in 30 seconds, and the FTSTS measures the time it takes to stand 5 times quickly. Both chair stand tests utilize a standard 17- to 18-inch chair without armrests, and the participant starts from the middle of the chair with a straight back. There were 10 RCTs, 6 NRTs, 1 pre-post, and 2 time series studies. Of the 10 RCTs, a small ES (d = 0.41-0.48)21 and a large ES (d = 1.08)37 were demonstrated on the 30-second test and 3 studies showed medium to large ESs on the FTSTS (d = 0.50-0.77).38–40 In 5 NRT studies, the 30-second chair stand demonstrated small ESs (d = 0.20-0.41) in 2 studies26 , 41 and large ESs (1.07-1.32) in 3 studies.35 , 41 , 42 In NRT studies, the FTSTS test showed small to medium ESs in 2 studies (d = 0.44-0.71).31 , 43 Good to excellent test-retest reliability on the 30-second chair stand (ICC = 0.84, n = 58)28 and the FTSTS (ICC = 0.94, n = 12) have been reported.44 In addition, excellent interrater reliability on the 30-second chair stand (ICC = 1.0, n = 33) has been reported in older adults with ADRD.45

Table 2

Table 2

The Timed Up and Go (TUG) 46 test was used in 17 of 47 studies measuring functional mobility, including 12 RCTs, 2 NRTs, 2 single-group pre-post, and 1 time series study. For the TUG test, participants are asked to stand from the chair and walk 3 m around a cone, return to chair, and sit down. The TUG was performed at usual pace in these studies. Among the 12 RCTs, 6 reported small ESs (d = 0.23-0.34)6 , 38–40 , 47 , 48 and 1 reported a medium ES (d = 0.62).37 In the other 5 RCTs, the TUG showed minimal to no effect.21 , 39 , 42 , 49 , 50 Excellent relative test-retest reliability has been reported on the TUG (ICC ≥0.94) in older adults with cognitive impairment, ranging in severity from MCI to moderate dementia.28 , 29 , 51

The Performance-Oriented Mobility Assessment (POMA) was used in 6 studies, including 4 RCTs and 2 single-group pre-post studies. The POMA is a task-oriented test of gait and balance that contains 9 items (16 points) for balance assessment and 7 items (12 points) for gait assessment. A higher score on the POMA indicates a higher level of function. Medium to large positive ESs (d = 0.71-0.88) were demonstrated in the 2 RCTs,38 , 39 no meaningful ES in 1 RCT,50 and 1 RCT lacked data to calculate the ES.52 Notably, the 3 RCTs with calculated ESs also administered the TUG. Overall, the POMA yielded larger ESs than the TUG when administered in the same study. In people with dementia, excellent test-retest reliability was demonstrated in older adults with mild-moderate dementia (ICC = 0.96).51 Good interrater reliability (ICC = 0.97)53 and predictive validity for falls (within 3 months) has been demonstrated (sensitivity = 70%-85%, specificity = 51%-61%) for the POMA and its subtests.54 In the POMA, feasibility and predictive validity in people with dementia have been demonstrated, although found to be limited in individuals with advanced dementia.54

The Functional Independence Measure (FIM) indicates how much assistance is required to carry out activities of daily living.55 The FIM was used in 3 studies, including 2 RCTs and 1 NRT. The FIM contains 18 items composed of 13 motor tasks and 5 basic activities of daily living. Each task is rated on a 7-point ordinal scale that ranges from 1, indicating total assistance (fully dependent), to 7, indicating complete independence. The FIM total score ranges from 10 (lowest function) to 126 (highest function). A large ES (d = 1.45) was found in 1 RCT,56 and a small ES was found in the other RCT (d = 0.22-0.39)57 and the NRT (d = 0.28).41 Psychometric properties of the FIM were not available.

The Short Physical Performance Battery (SPPB) is a widely used test of lower extremity function in older adults and consists of 3 tasks: static standing balance, comfortable walking speed (8 ft, 3 m, or 4 m), and a timed, 5-time chair stand test. The SPPB was used in 2 RCTs, but data were not available to calculate the ESs. No significant improvement was reported on the total SPPB score in either of the studies.57 , 58 Psychometric properties of the SPPB components have been reported in the chair stands and gait speed as described later.

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Gait Measures

Studies that measured gait are summarized in Table 3. Gait speed (m/s) during a short-distance walk at usual (self-selected) pace and/or fast pace was used in 13 studies, including 9 RCTs, 2 NRTs, and 2 single-group pre-post design. A walking distance of 6 m was most commonly used, but distances of 5 m and 2.4 m were also utilized. Among the 9 RCTs, 5 demonstrated small-to-medium ESs for usual-paced gait speed (d = 0.20-0.57),21 , 40 , 68–70 and 1 demonstrated a large ES for fast-paced gait speed (d = 0.80).39 Two NRTs showed a medium ES for usual-paced gait speed (m/s) (d = 0.78)26 and a large ES for fast walking time (s) (d = 1.25).35 Timed gait speed has demonstrated good to excellent test-retest reliability in people with mild to severe dementia on the 6-m and 10-m walks (ICC = 0.86-0.98).29 , 71 In older adults with moderate to severe dementia, concurrent validity was reported between gait speed (m/s) and lower extremity function on the SPPB (r = 0.71).72

Table 3

Table 3

Quantitative gait analysis using instrumentation to gather spatial and temporal parameters of gait was used in 4 studies, including 2 RCTs and 2 NRTs. Instrumentation consisted of a single digital camera and kinematic software (1 study),73 the GAITRite Walkway System (2 studies),43 , 74 and the Bessou locometer (line or thread attached to a pulley) and SATEL software (1 study).75 Common spatial and temporal parameters across the studies using quantitative methods included gait speed (meters/second), stride length (meters), step length (meters), cadence (steps/minute), stride time (seconds), step width (meters), and double- or single-leg support (time or percentage of gait cycle). In older adults with moderate to severe dementia, concurrent validity was reported between GAITRite parameters (cadence, stride length, and stride velocity) and lower extremity function on the SPPB (r > 0.51).72

Among the 2 RCTs, small to large ESs were reported in parameters collected via the electronic walkway, including gait speed, stride length, stride time, and double-limb support, with 1 study reporting small to medium ESs (d = 0.40-0.56) during fast-paced walking,74 and the other RCT reporting large ESs (d = 1.18-2.37) during usual-paced walking.75 In the 2 NRTs, stride length improved in 1 study and was the only parameter that improved significantly, demonstrating a medium ES (d = 0.61).73 There was no effect in the other NRT.43 Quantitative gait analysis, using GAITRite, has demonstrated high test-retest reliability in people with ADRD, ranging from mild to severe disease (ICC = 0.97-0.98),29 and good test-retest reliability of velocity, cadence, step length, stride length, step width, and swing and stance times for all gait parameters in people with mild to moderate (ICC > 0.86)71 and moderate to severe ADRD (ICC > 0.91).72

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Balance Measures

Studies that measured balance are summarized in Table 4. The Berg Balance Scale (BBS), a measure of static and dynamic balance, is a 14-item test with a total of 56 points (a higher score indicates lower fall risk). The BBS was used in 9 studies, including 8 RCTs and 1 NRT. Among the 8 RCTs, 4 studies had ESs ranging from small to large (d = 0.29-2.52).48 , 56 , 77 , 78 In 1 RCT, improvement was statistically significant but the ES was minimal.61 In the NRT, a medium ES was reported (d = 0.51) but improvement was not statistically significant.42 For older adults with ADRD, excellent test-retest reliability (ICC = 0.95)79 and good to excellent interrater reliability have been reported (ICC = 0.72-0.99) on the BBS.45 , 79

Table 4

Table 4

The Functional Reach Test, a measure of dynamic balance, was used in 4 studies, including 3 RCTs and 1 time series study. Among the 3 RCTs, 2 reported medium to large ESs (d = 0.69-0.99).37 , 49 No meaningful ES was demonstrated in the other studies. Good test-retest reliability (ICC = 0.80) and interrater reliability (ICC = 0.79) have been reported in older adults with ADRD.79

The single-leg stance test was administered in 4 studies, including 2 RCTs, 1 NRT, and 1 time series study. In 1 RCT, significant improvement and small to large ESs were reported (d = 0.38-0.85)40; however, outcome data were not reported in the other RCT.70 No improvement was observed in the time series trial.59 Psychometric properties were not available.

The Frailty and Injuries Cooperative Studies of Intervention Techniques-Subtest 4 (FICSIT-4) to measure narrow-base stance time was used in 2 studies, 1 RCT and 1 NRT. The RCT intervention yielded a medium ES (d = 0.64)21 and the NRT a small ES (d = 0.38).26 Good relative test-retest reliability (ICC = 0.79, n = 58) has been reported in older adults with ADRD.28

Instrumented postural sway, a measure of body sway during static standing (normal-base, narrow-base, or varied surface), was administered in 4 studies, 2 RCTs and 2 NRTs. Reduced postural sway, suggesting improvement in postural control, was demonstrated with a large ES in 1 RCT (d = 0.64-0.89)78 and a small ES in the other RCT (d = 0.30).49 Significantly less postural sway was reported in both NRTs with a medium ES (d = 0.42),43 but outcome data were not provided for this measure in the other NRT.42 Excellent test-retest reliability (ICC = 0.91) has been reported for a static balance force plate composite measure under different sensory conditions (eyes open and closed standing on a firm surface, and eyes open and closed while standing on foam) in older adults with mild to moderate ADRD.49

The Figure-of-8 Walk (F8W) Test 80 was administered in 2 studies, 1 RCT and 1 NRT. The F8W requires a person to walk a figure of 8 around 2 cones placed 5 ft apart. Typical measurement parameters include speed, number of steps, and accuracy of walking.80 A small ES for speed was seen in the RCT (d = 0.28)21 and small ESs were demonstrated for increased speed and decreased oversteps in the NRT.26 The F8W has demonstrated excellent relative test-retest reliability in older adults with mild to moderate dementia (ICC = 0.91; n = 46).28

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Strength Measures

Studies that measured strength are summarized in Table 5. Strength measures included isometric measures, using handheld dynamometers, of handgrip and lower extremity strength and dynamic measures using a 1-repetition maximum (RM) test for lower extremity strength. Handgrip strength was used in 8 studies, including 4 RCTs, 2 NRTs, and 2 pre-post design. Among the RCTs, small to medium ESs (d = 0.34-0.70) were reported in 2 studies.40 , 62 Isometric lower extremity strength of the knee extensors17 , 21 , 26 , 39 , 40 and hip flexors and ankle dorsiflexors17 , 39 , 40 was measured in 6 studies, including 4 RCTs, 1 NRT, and 1 pre-/poststudy. Among the RCTs, small to medium ESs (d = 0.26-0.63) were reported for lower extremity isometric strength.21 , 26 Lower extremity 1-RM tests were used in 5 studies, including 3 RCTs and 2 NRTs. In the RCTs, large ESs (d = 1.38-1.39) were reported on leg press and hip abductor dynamic muscle strength tests.27 , 38 , 39 , 43 Excellent test-retest reliability has been reported in individuals with mild to moderate ADRD for handgrip strength, taking the best of 3 maximum efforts to squeeze a dynamometer with the dominant hand with the arm extended (ICC > 0.90).28 Excellent test-retest reliability has also been reported for handheld dynamometer measures of maximum effort isometric knee extension (seated, 90° knee flexion), placed just proximal to the malleoli and using the best of 2 trials for individuals with mild to severe dementia (ICC > 0.95).81

Table 5

Table 5

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DISCUSSION

Fitness, functional mobility, gait, balance, and strength represent important domains of physical function for older adults. Mounting evidence from both RCTs and other intervention trials suggests that each of these domains can improve in people with ADRD.83 This scoping review identified commonly used physical performance outcome measures that are responsive and reliable for use in exercise interventions for older adults with ADRD. Use of these measures in future research has the potential to lead to improved clinical care for this vulnerable and growing population.

Physical fitness, including cardiorespiratory and muscular fitness, is associated with decreased morbidity and mortality and is important for maintaining relative independence in older adults.14 In studies included in this review, fitness was most often measured with the 6MWT, which was found to be sensitive to change (most studies reported medium to large ES), and reliable in subjects with ADRD. Furthermore, the 6MWT has been widely used to assess exercise capacity in noncognitively impaired older adult populations and also provides information on an individual's functional mobility.84 , 85 Minimal detectable change (MDC), the magnitude of change that exceeds expected measurement error and variability on the 6MWT (MDC 90th percentile), was reported to be 33.47 m in older adults with ADRD.29 Although few studies used the 2MWT, and reliability was not available, this test is shorter than the 6MWT and may be more feasible for individuals with severe cognitive impairment.

Measures of functional mobility are important for evaluating risk for progressive and/or catastrophic mobility disability86 as well as outcomes of exercise intervention studies. The most frequent measures used to assess functional mobility outcomes in response to exercise interventions were the TUG and chair stand tests (FTSTS or 30-second chair stand). Both tests had good to excellent reliability in people with ADRD. Reliable measures of lower extremity isometric strength are predictive of sit-to-stand performance in older adults with ADRD,81 suggesting that handheld dynamometer measurement may enhance assessment of lower extremity function in older adults with ADRD.

The sensitivity of the TUG to detect clinically meaningful change may decrease as dementia severity increases. This is suggested by MDC values on the TUG that range from 4.0929 to 8.07 seconds28 in older adults with ADRD compared with a reported MDC of 1.52 seconds in people with MCI.29 It is also interesting to note that a higher MDC for the 30-second chair stand has been reported in individuals with MCI (MDC = 4.21 stands) than those with moderate dementia (MDC = 2.3 stands).

Improvement on tests of functional mobility is clinically important because poor performance on these tests is associated with increased risk for adverse health events, including falls.87 , 88 The FIM, used in 3 studies, is more time-consuming and dependent on ratings from trained personnel. However, it may be feasible to obtain useful FIM ratings from caregivers since moderate to high correlations (r = 0.62-0.91) have been reported between caregiver-reported FIM scores and investigator observation-derived FIM scores (real-time or videotaped).89

Quantitative measures of gait allow for assessment of temporal and spatial characteristics of walking, including gait speed, step length, swing time, and stance time step. The 6-m walk test was used as a gait outcome measure in multiple exercise intervention studies. Short-distance (6-10 m) gait speed has demonstrated good to excellent reliability in people with dementia;29 , 71 it is also inexpensive and easy to measure in clinical and research settings. Five- to 10-m walking distance tests have demonstrated feasibility and are psychometrically sound in older adults without dementia.90 However, although we included 3 studies that used 2.4-m distance, this shorter distance is not recommended due to low concurrent validity with longer distance walk tests.91 In this review, gait speed was responsive to exercise interventions in older adults with ADRD, demonstrating small to medium ESs in more than half of the RCTs. Additional quantitative temporal and spatial gait parameters, including stride length, stride time, and double limb support, were also responsive to exercise interventions as demonstrated by medium to large effect sizes during usual- and fast-paced walking. Reduced gait speed, stride length, and increased double support have been associated with instability and falls in older adults with dementia,72 suggesting that improvements in these parameters are clinically important.

In nursing home residents with moderate to severe dementia, gait changes measured with an electronic walkway system (GAITRite) were significant predictors of at least 1 fall, gathered from a computerized fall incident report system.54 Specifically, reduced gait speed (odds ratio = 1.22; 95% confidence interval = 1.04-1.43) and reduced mean stride length (odds ratio = 1.19; 95% confidence interval = 1.03-1.40) were significant predictors of a fall within 3 months. Sensitivity was 82% for velocity and 86% for mean stride length. Specificity was 52% for velocity and mean stride length.54 The MDC at the 90th percentile for gait speed is 0.09 m/s.29

Decreased usual gait speed is a consistent risk factor for disability, cognitive impairment, institutionalization, falls, and mortality.92 Researchers have also suggested that gait speed alone can be used as a predictor of mobility disability, dementia, and mortality in community-dwelling older adults.92 Further research is needed to determine whether improved gait speed reduces the onset of mobility disability and mortality in older adults with ADRD.

Performance on balance tests is nearly as prognostic in predicting adverse health events in older adults as usual gait speed.88 Balance deficits are present even at the earliest stages of ADRD, suggesting that early identification and balance training could improve postural stability and reduce risk for falls over the course of disease.93 , 94 Balance measures used in the reviewed studies were the BBS, Functional Reach, Single-Leg Stance, the FICSIT-4, and the Figure-of-8 test. In this scoping review, the BBS, a measure of static and dynamic balance, was the most frequently used balance test. Lower scores on the BBS have been associated with falls in older adults with moderate to severe dementia.72 In this review, 4 of 8 RCTs reported small to large ESs, suggesting reduced fall risk in response to exercise interventions. Excellent relative test-retest reliability and good to excellent interrater reliability support the application of the BBS in people with dementia; however, further research is needed considering a ceiling effect on the BBS in other older adult populations.28 MDCs, at the 95th percentile (n = 15), of 16.7 for the BBS and 12.6 cm for the Functional Reach have been reported in people with mild to moderate dementia. However, both tests had high standard error of measurement and enough disagreement of 2 evaluators in one session to cause problems with interpretation.79 Therefore, further study of MDCs is needed for the BBS and Functional Reach Test in people with ADRD.

Similar to quantitative gait analysis, instrumented postural sway provides quantitative data beyond that which can be attained with traditional clinical performance-based tests,95 and postural sway measures represent independent domains of mobility in healthy community-dwelling older adults and individuals with Parkinson's disease,96 , 97 which is likely similar in individuals with ADRD. In response to exercise interventions, a reduction of postural sway was detected during static standing in 2 of the 4 RCTs.

This scoping review of the literature is based on a broad and comprehensive literature search, conducted with the assistance of a research librarian. Each relevant article identified was reviewed in pairs, with each partner completing the abstraction process independently and any differences in ratings being resolved by consensus between the reviewers or among the entire group. The results of this review provide information on responsiveness and reliability, making it an excellent resource for researchers and clinicians implementing exercise interventions with this population. Limitations to the current review are related to scoping review methodology. No quality appraisal of studies was conducted. Across all studies included in this review, there was considerable variability in the characteristics reported of the exercise interventions. Although these characteristics (eg, components, dose, and duration) are summarized in measurement tables, they were not considered in evaluating the sensitivity or strength of the outcome measures, thus some differences in ES might be due to differences in the programs, rather than in the measures themselves. However, since the outcome measures that were ultimately included in the review were used across multiple studies, this limitation is at least partially mitigated.

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CONCLUSIONS

There are challenges in evaluating the effects of exercise interventions for older adults with ADRD, particularly as cognitive impairment progresses. Physical performance outcome measures used in older adults without cognitive impairment may not translate to intervention work with individuals who have ADRD. In studies of older adults with ADRD, the 6MWT, TUG, repeated chair stand tests, short-distance gait speed, the BBS, and isometric strength are frequently used and responsive to exercise interventions. In addition, good to excellent reliability on these outcome measures has been reported in individuals with mild to moderate dementia. Further research is needed to identify optimal outcome measures for individuals with severe dementia. The results of this review have the potential to aid clinicians and researchers in selecting appropriate measures to evaluate physical performance outcomes in response to exercise interventions in older adults with ADRD.

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                  Appendix A: Search Strategies (PubMed)

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                  Appendix B: Formula for Effect Size Calculation (Cohen's d)

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                  Keywords:

                  Alzheimer disease and related dementia; exercise interventions; outcome measures

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