Mobility In Community-dwelling Older Adults Research Articles

Comparison of Self-Reported and Capacity-Based Measures of Mobility in Community-Dwelling Older Adults in Nigeria: The Mediating Role of Age, Cognitive Status, and Chronic Conditions.

Although the association between self-reported and capacity-based mobility outcomes is prominently researched, the pathways through which self-reported measures affect capacity-based measures remains poorly understood. Therefore, our study examines the association between self-reported and capacity-based mobility measures and explores which mobility determinants mediate the association in Nigerian community-dwelling older adults. This cross-sectional study included 169 older adults [mean age (SD) = 67.7 (7.0)]. Capacity-based mobility outcomes included the Short Physical Performance Battery (SPPB), the 6-Minute Walk Test (6MWT), and the 10-Meter Walk Test (10mWT), whereas the self-reported mobility outcomes included the Lower Extremity Functional scale (LEFS), the Life Space Questionnaire (LSQ), and the Mänty Preclinical Mobility scale (inability to walk 2 km, 0.5 km, or climb a flight of stairs). Spearman's correlations were conducted to examine the relationship between self-reported and capacity-based mobility measures, whereas structural equation modeling was used to determine the mediators. The correlation between SPPB and LEFS (rho = 0.284) and 0.5 km (rho = -0.251) were fair, whereas the correlation between SPPB and inability to walk 2 km (rho = -0.244) and inability to climb a flight of stairs (rho = -0.190) were poor. Similarly, correlations between 6MWT and the LEFS (rho = 0.286), inability to walk 2 km (rho = -0.269), and 0.5 km (rho = -0.303) were fair. The 6WMT was poorly correlated with inability to climb one flight of stairs (rho = -0.233). The LSQ was not correlated with SPPB or 10mWT. Age was the only significant mediator, whereas the number of chronic conditions and cognitive status were not. The correlation between self-reported and capacity-based mobility outcomes in older adults in Nigeria is lower than those in developed countries. Our analysis provides a foundation to explore mobility determinants that could be predictive mediators for mobility outcomes, making meaningful contributions to explaining mobility complexities.

Exploring Physical and Cognitive Factors Impacting Life-Space Mobility in Community-Dwelling Older Adults

Aim: To investigate the factors and impact strength affecting mobility in community-dwelling older adults using a general linear model that can adequately address the issue of variables' distribution for more robust results. Methods: This cross-sectional study involving 103 participants was conducted to identify the factors affecting the Life-Space Assessment scores using a general linear model based on the data imputed using the hot-deck method. A complete case analysis was performed as a sensitivity analysis. Results and Conclusions: Three factors associated with life-space mobility were included in the model: walking speed, pain, and cognitive function.

Factors influencing mobility in community-dwelling older adults during the early COVID-19 pandemic: a cross-sectional study

BackgroundIn older adults, mobility is important for maintaining their independence and quality of life, and it influences their physical, cognitive, and social health. This study aimed to identify the physical and psychosocial factors that affected the mobility of community-dwelling older adults, aged 65 years or older, who were socially isolated during the coronavirus disease 2019 (COVID-19) pandemic due to stay-at-home policies.MethodsThe participants in this study were 214 community-dwelling older adults in Korea, and a cross-sectional survey was conducted from December 2020 to January 2021. Variables included participants’ general characteristics, mobility, sitting time, depression, social support, and cognitive function.ResultsMultiple linear regression analysis showed that the factors influencing older adults’ mobility during the COVID-19 pandemic were depression (β=-0.29, p < .001), age (65–74 years old) (β = 0.19, p = .002), a lower level of education (β=-0.17, p = .006), two or more comorbidities (β=-0.18, p = .001), sitting time (β=-0.17, p = .004), and the ability to drive a vehicle (β = 0.14, p = .017).ConclusionsHome healthcare interventions are needed to limit psychosocial issues and improve mobility for older adults who had limited mobility during the COVID-19 pandemic.

Home-Based Indoor Physical Activity Programs for Community-Dwelling Older Adults: A Systematic Review.

Home-based exercise programs are a good strategy to promote benefits to health for people who cannot visit gyms, clinics, or have limited time for physical activity outside. To synthesize the effect of home-based indoor physical activity on psychosocial outcomes and mobility in community-dwelling older adults. A comprehensive search was conducted in the MEDLINE, PubMed, Embase, SPORTDiscus, Cochrane Library, Scopus, and Google Scholar databases. A total of 11 studies (13 publications) were included involving a total of 1004 older adults. A systematic review of randomized controlled trials was conducted using the aforementioned 7 databases. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. Level 2. Two authors independently selected studies, extracted data, and determined the risk of bias and evidence level using the Grading quality of evidence and strength of recommendations (GRADE) guidelines. We conducted a synthesis without meta-analysis (SWiM) to assess the outcome. There is moderately certain evidence that home-based exercise programs reduced the fear of falling. Psychosocial (mental health and quality of life) and mobility outcomes may improve after participating in the intervention inside the home. The review found very low to certain evidence that home-based exercises programs improved psychosocial outcomes (mental health and quality of life) and walking speed (mobility). Moderately certain evidence suggests that home-based exercises improved fear of falling. CRD42020182008.

Critically appraised paper: Timing and coordination training does not enhance standard treatment benefit on mobility in community-dwelling older adults [commentary].

Critically appraised paper: Timing and coordination training does not enhance standard treatment benefit on mobility in community-dwelling older adults [commentary].

Critically appraised paper: Timing and coordination training does not enhance standard treatment benefit on mobility in community-dwelling older adults [synopsis].

Critically appraised paper: Timing and coordination training does not enhance standard treatment benefit on mobility in community-dwelling older adults [synopsis].

Dual Roles of Cardiorespiratory Fitness and Fatigability in the Life-Space Mobility of Older Adults: The Study of Muscle, Mobility and Aging (SOMMA).

Cardiorespiratory fitness and perceived fatigability are interrelated components of physical capacity that may jointly influence movement within one's living environment (life-space mobility). We examined whether fitness and fatigability were associated with life-space mobility in community-dwelling older adults, and whether the association of fitness with life-space varied by the level of perceived fatigability. Participants were from the Study of Muscle, Mobility and Aging (SOMMA) baseline cohort (N = 775, mean age 76.1 years). Life Space Assessment scores incorporated level, frequency, and assistance used (personal, devices) for life-space mobility. Fitness was measured as VO2peak from symptom-limited treadmill testing. Fatigability cut-points included: (i) Borg Rating of Perceived Exertion (RPE) ≥ 10 after a fixed-speed (1.5 mph) treadmill test, (ii) the Pittsburgh Fatigability Scale (PFS) Physical ≥ 15, and (iii) PFS Mental ≥ 13. The total count of cut-points was used as a composite fatigability measure (range: 0-3). Linear regressions were adjusted for demographic, lifestyle, and health confounders. Better fitness was associated with greater life-space, but the association plateaued at higher fitness levels (VO2peak > 18). Life-space was significantly lower for individuals meeting ≥2 fatigability criteria (vs none), attributable mainly to more severe physical, but not mental, fatigability. In moderation analyses, the fitness-life-space association was significant only for those with RPE ≥ 10 but did not differ by PFS. Fitness below a critically low threshold was associated with limited life-space mobility, suggesting that certain older individuals may need to operate close to their maximum aerobic capacity to traverse daily environments; these associations were driven by those with more severe physical fatigability.

Validation of cutoff values of the modified five-repetition Sit-to-Stand and One-Leg Stand tests to discriminate life-space mobility in community-dwelling older adults needing support or care

Validation of cutoff values of the modified five-repetition Sit-to-Stand and One-Leg Stand tests to discriminate life-space mobility in community-dwelling older adults needing support or care

The Effect of Dual-Task on Manual Dexterity and Functional Mobility in Community-Dwelling Older Adults

The Effect of Dual-Task on Manual Dexterity and Functional Mobility in Community-Dwelling Older Adults

Community-based group physical activity and/or nutrition interventions to promote mobility in older adults: an umbrella review

BackgroundPhysical activity and a healthy diet are important in helping to maintain mobility with aging. This umbrella review aims to identify group-based physical activity and/or nutrition interventions for community-dwelling older adults that improve mobility-related outcomes.MethodsFive electronic databases (MEDLINE, Embase, CINAHL, Cochrane CENTRAL, Sociological s) were searched from inception to December 2021. Eligibility criteria included systematic reviews exploring the effectiveness of physical activity or structured exercise, alone or combined with nutrition interventions on mobility-related outcomes (aerobic capacity, physical function, balance, falls/safety, muscle strength, health-related quality of life/wellbeing). Interventions must have been delivered in a group setting to community-dwelling older adults aged 55+. Two reviewers independently performed eligibility screening, critical appraisal (using AMSTAR 2) and data extraction. The GRADE approach was used to reflect the certainty of evidence based on the size of the effect within each mobility-related outcome category. Older adult/provider research partners informed data synthesis and results presentation.ResultsIn total, 62 systematic reviews (1 high, 21 moderate, 40 low/critically low quality) were identified; 53 included physical activity only, and nine included both physical activity and nutritional supplements. No reviews included nutrition interventions alone. Combined aerobic/resistance, general physical activity, and mind-body exercise all improved physical function and balance (moderate-high certainty). Aerobic/resistance training improved aerobic capacity (high certainty). Resistance training and general physical activity improved muscle strength (moderate certainty). Aerobic/resistance training and general physical activity are likely to reduce falls among older adults (moderate certainty). There was no evidence of benefit for nutritional supplementation with physical activity.ConclusionsGroup-based physical activity interventions that combine aerobic and resistance, general PA and mind-body exercise can improve measures of mobility in community-dwelling older adults. We found no reviews focused on nutrition only, highlighting a gap in the literature.

Group-based nutrition interventions to promote healthy eating and mobility in community-dwelling older adults: a systematic review.

To identify the efficacy of group-based nutrition interventions to increase healthy eating, reduce nutrition risk, improve nutritional status and improve physical mobility among community-dwelling older adults. Systematic review. Electronic databases MEDLINE, CINAHL, EMBASE, PsycINFO and Sociological Abstracts were searched on July 15, 2020 for studies published in English since January 2010. Study selection, critical appraisal (using the Joanna Briggs Institute's tools) and data extraction were performed in duplicate by two independent reviewers. Nutrition interventions delivered to groups in community-based settings were eligible. Studies delivered in acute or long-term care settings were excluded. Community-dwelling older adults aged 55+ years. Studies targeting specific disease populations or promoting weight loss were excluded. Thirty-one experimental and quasi-experimental studies with generally unclear to high risk of bias were included. Interventions included nutrition education with behaviour change techniques (BCT) (e.g. goal setting, interactive cooking demonstrations) (n 21), didactic nutrition education (n 4), interactive nutrition education (n 2), food access (n 2) and nutrition education with BCT and food access (n 2). Group-based nutrition education with BCT demonstrated the most promise in improving food and fluid intake, nutritional status and healthy eating knowledge compared with baseline or control. The impact on mobility outcomes was unclear. Group-based nutrition education with BCT demonstrated the most promise for improving healthy eating among community-dwelling older adults. Our findings should be interpreted with caution related to generally low certainty, unclear to high risk of bias and high heterogeneity across interventions and outcomes. Higher quality research in group-based nutrition education for older adults is needed.

Community-based physical activity and/or nutrition interventions to promote mobility in older adults: An umbrella review.

Background: Physical activity and a healthy diet are important in helping to maintain mobility and quality of life with aging. Delivery of physical activity and nutrition interventions in a group setting adds the benefits of social participation. Several published systematic reviews have explored a broad range of PA and/or nutrition interventions for older adults, making it challenging to bring together the best scientific evidence to inform program design and to inform multicomponent intervention development. This umbrella review aims to identify group-based physical activity and nutrition interventions for community-dwelling older adults that improve mobility. Methods: Five electronic databases (MEDLINE, Embase, CINAHL, Cochrane CENTRAL, Sociological Abstracts) were searched from inception to April 28, 2020. Eligibility criteria included systematic reviews exploring the effectiveness of physical activity and/or nutrition interventions, delivered in a group setting for community-dwelling older adults. Two reviewers independently performed eligibility screening, critical appraisal (using AMSTAR 2) and data extraction. The GRADE approach was used to assess the overall certainty of the evidence. Older adult/provider research partners informed data synthesis and results presentation. Results: In total, 54 systematic reviews (1 high, 21 moderate, 32 low/critically low quality) were identified; 46 included physical activity only, and eight included both physical activity and nutritional supplements. No reviews included nutrition interventions alone. Combined aerobic/resistance, general physical activity, and mind-body exercise all improved physical function and balance (moderate-high certainty). Aerobic/resistance training improved aerobic capacity (high certainty). Resistance training and general physical activity improved muscle strength (moderate certainty). Aerobic/resistance training and general physical activity are likely to reduce falls among older adults (moderate certainty). There was no evidence of benefit for nutritional supplementation with physical activity. Conclusions: Multicomponent group-based physical activity interventions can improve measures of mobility in community-dwelling older adults. We found no reviews focused on nutrition only, highlighting a gap in the literature.

Facilitators and barriers to real-life mobility in community-dwelling older adults: a narrative review of accelerometry- and global positioning system-based studies.

Real-life mobility, also called “enacted” mobility, characterizes an individual’s activity and participation in the community. Real-life mobility may be facilitated or hindered by a variety of factors, such as physical abilities, cognitive function, psychosocial aspects, and external environment characteristics. Advances in technology have allowed for objective quantification of real-life mobility using wearable sensors, specifically, accelerometry and global positioning systems (GPSs). In this review article, first, we summarize the common mobility measures extracted from accelerometry and GPS. Second, we summarize studies assessing the associations of facilitators and barriers influencing mobility of community-dwelling older adults with mobility measures from sensor technology. We found the most used accelerometry measures focus on the duration and intensity of activity in daily life. Gait quality measures, e.g., cadence, variability, and symmetry, are not usually included. GPS has been used to investigate mobility behavior, such as spatial and temporal measures of path traveled, location nodes traversed, and mode of transportation. Factors of note that facilitate/hinder community mobility were cognition and psychosocial influences. Fewer studies have included the influence of external environments, such as sidewalk quality, and socio-economic status in defining enacted mobility. Increasing our understanding of the facilitators and barriers to enacted mobility can inform wearable technology-enabled interventions targeted at delaying mobility-related disability and improving participation of older adults in the community.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40520-022-02096-x.

Mobility enhancement among older adults 75\u2009+\u2009in rural areas: Study protocol of the MOBILE randomized controlled trial

BackgroundMaintaining mobility in old age is crucial for healthy ageing including delaying the onset and progress of frailty. However, the extent of an individuals´ mobility relies largely on their personal, social, and environmental resources as outlined in the Life-Space Constriction Model. Recent studies mainly focus on facilitating habitual out-of-home mobility by fostering one type of resources only. The MOBILE trial aims at testing whether tablet-assisted motivational counselling enhances the mobility of community-dwelling older adults by addressing personal, social, and environmental resources.MethodsIn the MOBILE randomized controlled trial, we plan to enrol 254 community-dwelling older adults aged 75 and older from Havelland, a rural area in Germany. The intervention group will receive a tablet-assisted motivational counselling at the participant´s home and two follow-up telephone sessions. Main focus of the counselling sessions lays on setting and adapting individual mobility goals and applying action planning and habit formation strategies by incorporating the personal social network and regional opportunities for engaging in mobility related activities. The control group will receive postal general health information. The primary mobility outcome is time out-of-home assessed by GPS (GPS.Rec2.0-App) at three points in time (baseline, after one month, and after three months for seven consecutive days each). Secondary outcomes are the size of the GPS-derived life-space convex hull, self-reported life-space mobility (LSA-D), physical activity (IPAQ), depressive symptoms (GDS), frailty phenotype, and health status (SF-12).DiscussionThe MOBILE trial will test the effect of a motivational counselling intervention on out-of-home mobility in community-dwelling older adults. Novel aspects of the MOBILE trial include the preventive multi-level intervention approach in combination with easy-to-use technology. The ecological approach ensures low-threshold implementation, which increases the benefit for the people in the region.Trial registrationThe MOBILE trial is prospectively registered at DRKS (Deutsches Register Klinischer Studien, German Registry of Clinical Trials) DRKS00025230. Registered 5 May 2021.

Effect of life-space mobility on subjective well-being in aged home-based rehabilitation users with different levels of independence in activities of daily living.

[Purpose] The relationship between quality of life and life-space mobility in community-dwelling older adults has recently been reported. The present study aimed to elucidate this relationship in home-based rehabilitation users with limited life-space mobility and loss of independence in activities of daily living. [Participants and Methods] The study population comprised 33 home-based rehabilitation users. The participants were expected to have a wide range of the level of independence in activities of daily living; therefore, they were categorized into three groups according to the Barthel Index score: independent (95–100 points), moderately disabled (90–65 points), and severely disabled (60–0 points) groups. We examined the relationships among the Philadelphia Geriatric Center Morale Scale, Life-Space Assessment, and Barthel Index scores and age. [Results] We detected a strong positive correlation between the Philadelphia Geriatric Center Morale Scale and Life-Space Assessment scores in the independent group; however, no significant correlations were observed in the moderately and severely disabled groups. [Conclusion] Our findings suggest a relationship between subjective well-being and life-space mobility in home-based rehabilitation users who are mostly independent in activities of daily living. However, owing to the small sample size and characteristics of the scales used in this study, further studies are warranted to verify these results.

Short distance analysis of the 400-meter walk test of mobility in community-dwelling older adults

The 400-meter walk test (400MWT) is used to assess cardiovascular and pulmonary fitness or to predict adverse outcomes such as mobility disability. Additionally, short tests of walking such as the 4- or 8-meter walk test are administered to predict mortality, falls and other events. It remains uncertain if and how an integrated measurement of a short distance during 400MWT can replace an additional short distance measurement which would be clinically useful. How do short distance (i.e. segment) measurements of gait speed and walk ratio during a 400MWT of mobility compare to those from an additional 8-meter walk test? A 400MWT and a separate 8-meter walk test were performed by 148 community-dwelling older adults (mean age 80.4 ± 4.4 years) using an instrumented walkway. Gait speed and walk ratio (i.e. step length divided by step frequency) of single segments of the 400MWT were strongly associated with gait speed (r ≥ 0.91) and walk ratio (r ≥ 0.93) of an 8-meter walk test with best agreement in the middle part 20-meter walk during the 400MWT. Mean gait speed of all single walks on the instrumented walkway during the 400MWT was faster than the mean gait speed of the total 400MWT. A single walk of the 6th to 10th 20-meter walk during the 400MWT can be used as a substitute to an additional short distance trial. Furthermore, the awareness of being measured is higher on an instrumented walkway and possibly increases the motivation to overperform.

Use of GPS Tracking Technology to Measure Mobility in Older Adults: A Systematic Review

Global positioning system (GPS) tracking technology is increasingly used in aging research to objectively measure the spatial and temporal aspects of mobility in older adults. The review aims to systematically synthesize the literature to identify GPS-driven mobility measures and potential determinants of mobility limitation for community-dwelling older adults. A systematic search of six electronic databases was conducted. A total of 4897 articles were found with 2578 left to review after deduplication. Twenty-five studies met inclusion criteria: 24 cross-sectional studies and one follow-up study that measured mobility changes over time. Various types of GPS devices were used, including smartphones, GPS watches, or portable data logging kits. The GPS tracking period ranged from 1 to 30 days. The daily device wear time varied from 10 to 24 hours. Commonly reported GPS-based mobility measures included time out of home, distance moved, the number of out-of-home trips or walking tracts, the number of visited places, life-space area, and walking speed. Twenty-one studies reported some aspects of demographic, physical, psychosocial, or environmental factors related to the levels of GPS-based mobility. GPS tracking technology can continuously record individuals’ activities and functional abilities within their life space. We found that there was heterogeneity in ways of applying GPS technology and defining and measuring mobility in community-dwelling older adults. Given the lack of consistency in GPS-based mobility assessment, a clear definition of mobility and standardization of GPS data collection and analysis are required for comparison across studies and better understanding determinants of mobility limitation in community-dwelling older adults.

Associations Between Cognitive Function, Balance, and Mobility in Community-Dwelling Older Adults With COPD

Older adults with chronic obstructive pulmonary disease (COPD) are at risk for physical and cognitive impairment. Cognitive function is associated with falls in older adults however it is unknown if a relationship exists between cognitive function and falls in COPD. The aim of this study was to examine the relationships between cognitive function and balance and mobility in older adults with COPD. A secondary analysis was performed using data from the 2010 wave of the Health and Retirement Study (HRS) (N=4051). Cognitive (immediate and delayed recall, executive function) and physical (gait speed, tandem balance time) measure data was extracted from older adults with COPD (N=382) and an age matched control group without COPD (N=382) who met inclusion/exclusion criteria. Multivariate linear regression modeling was performed to examine associations between cognitive function and mobility or balance while controlling for age, gender, BMI, grip strength, and education. We found that in COPD, immediate word recall, delayed word recall, orientation, and executive function (β ranging from 0.004-0.02) were significantly associated with gait speed while only delayed word recall (β = 0.122, p < .05) was associated with tandem balance. These same associations did not exist in those without COPD. In older adults with COPD, cognitive function is associated with balance and mobility. Screening for cognitive function, specifically delayed recall, should be a part of the management of falls in this population.

Modifiable factors related to life-space mobility in community-dwelling older adults: results from the Canadian Longitudinal Study on Aging

BackgroundThe most common methods for measuring mobility in older adulthood include performance-based tests, such as the Timed-Up-and-Go and gait speed. While these measures have strong predictive validity for adverse outcomes, they are limited to assessing what older adults do in standardized settings, rather than what they do in their daily life. Life-space mobility, which is the ability to move within environments that expand from one’s home to the greater community, has been proposed as a more comprehensive measure of mobility. The aim of this study was to determine the association between modifiable factors and life-space mobility in older adults enrolled in the Canadian Longitudinal Study on Aging (CLSA).MethodsLife-space mobility was measured using the Life Space Index (LSI). Explanatory factors included physical, psychosocial and cognitive determinants, as well as pain, fatigue, driving status, nutrition, body mass index, smoking status, and vision. To estimate the association between the LSI and explanatory variables, univariate and multivariable ordinary least squares regression analyses were performed.ResultsAll adults 65 years and older (n = 12,646) were included in the analysis. Fifty percent were women and the mean age was 73.0 (SD5.7). The mean LSI score was 80.5, indicating that, on average, the sample was able to move outside of their neighborhood independently. All explanatory variables were significantly associated with the LSI except for balance and memory. The top 3 variables that explained the most variation in the LSI were driving, social support and walking speed.ConclusionTo our knowledge, this was the first study to examine the association between life-space mobility and a comprehensive set of modifiable factors that were selected based on a theoretical framework and existing research evidence. This study had two important messages. First, driving, social support and walking speed emerged as the most significant correlates of life-space mobility in older adults. Second, life-space mobility is multifactorial and interventions that are pragmatic in their design and testing are needed that consider the complexity involved. A multi-disciplinary approach to examining life-space mobility in older adults is needed to optimize opportunities for healthy aging and develop strategies that support mobility in older adulthood.

Rate of Force Development as a Predictor of Mobility in Community-dwelling Older Adults.

Rate of force development (RFD) is influential, and possibly more influential than other muscular performance parameters, for mobility in older adults. However, only a few studies have investigated this matter, and this has not been examined for the plantar flexors (PFs). The purpose of this study was to examine the contribution of PF RFD and other common tests of muscular performance to Up-and-Go (UG) performance and walking speed (WS) in older adults. Twenty-six (19 females) healthy, community-dwelling older adults (73.7 ± 4.9 years) were recruited from a senior citizen center for this observational study. Handgrip strength, UG performance, as well as preferred and maximal WS were obtained. Time taken to complete 5-chair rises and the number of chair rises completed in 30 seconds were recorded. Rate of force development of the PFs was obtained during a rapid, bilateral calf raise performed on a force plate. Hierarchical multiple linear regression was used to identify significant predictors, after adjusting for physical activity level and body mass index, of mobility (ie, UG, preferred and maximal WS). No muscular performance variables correlated with preferred WS. Rate of force development (adjusted R2 = 0.356; P = .008) and handgrip strength (adjusted R2 = 0.293; P = .026) were the only predictors of maximal WS and accounted for a 21.7% and 16.1% change in R2, respectively, after accounting for physical activity level and body mass index. Rate of force development was the only predictor of UG performance (adjusted R2 = 0.212; P = .006) and accounted for a 29.2% change in R2 after adjustment variables were applied. Compared to common assessments of muscular performance, such as handgrip strength and chair rise performance, PF RFD was a greater predictor of mobility in older adults. These findings, in conjunction with recent reports, indicate that the assessment of RFD likely complements strength testing, thereby enabling a more robust assessment of functional decline in older adults.