Validity of the Gait Variability Index in older adults: Effect of aging and mobility impairments
Introduction
Gait variability, defined as the fluctuation in spatiotemporal characteristics between steps, is a sensitive indicator of mobility deficits [1]. For example, variability in spatiotemporal parameters is reported to predict mobility deficits and future falls better than the mean of spatiotemporal parameters in older adults [2]. Gait variability is altered by pathological conditions of disease and injury [3]. An investigation of the magnitude of these fluctuations has received considerable attention and is the focus of the current study. Particularly, the magnitude in gait variability is an important outcome measure in older adults since altered gait variability has shown to be associated with advancing age, mobility deficits, cognitive impairments and fall risk [4], [5], [6], [7]. A majority of the literature in older adults report that gait variability is increased in older adults [1]. However, decreased gait variability has also been reported in some spatiotemporal parameters (such as step width) and related to mobility deficits [8]. Despite the mounting evidence supporting use of gait variability as an outcome measure in the older adult population, there has been limited use of gait variability measures in clinical settings or in randomized controlled trials.
The lack of widespread use of gait variability as an outcome measure may, in part, be due to methodological challenges [9]. First, it is unclear which spatiotemporal measures are of greatest importance when assessing gait variability. Variability has been reported for at least 11 spatiotemporal parameters, but it is unclear which are most relevant to mobility function and the deficits that they reflect. For instance, step width variability was associated with age-related sensory impairments in a study by Brach et al. [10], whereas Richardson et al. reported that step time and not step width variability was associated with sensory impairments [11]. Second, there is a lack of consensus regarding how best to quantify gait variability [e.g., standard deviation (SD), coefficient of variation (CV)]. Some researchers have proposed that until a consensus can be reached, gait variability should be analyzed multiple ways [9]. Third, for individuals with impaired mobility the increase in gait variability can be observed across many different spatiotemporal parameters. This inter-dependence confounds statistical analysis because it is not clear which parameters are the best indicators of mobility deficits.
These methodological issues motivated the development of the Gait Variability Index (GVI). The GVI is a conglomerate measure of gait variability derived from nine spatiotemporal parameters and was developed to improve objective quantification of gait variability [12]. Preliminary validity was demonstrated by a decrease in GVI for individuals with Friedreich's Ataxia, suggesting that the GVI was linked to mobility function [12]. While the GVI seems to be a promising outcome measure because it avoids some of the methodological problems surrounding variability measures, it is not yet validated as an outcome measure in older adults. Therefore, the purpose of this study was to investigate the validity of the GVI as an outcome measure of mobility deficits in older adults.
Section snippets
Participants
This study retrospectively analyzed data pooled from 5 studies (Table 1). Participants aged 18–90 years (n = 186) were included. Participant data was categorized into two broad categories: younger adults (YA) less than 65 years of age and older adults (OA) greater than or equal to 65 years of age. Study protocols were approved by the Institutional Review Boards at the respective institutions and all participants gave their informed consent before participation.
Procedures
Procedures of included studies have
Results
Data reduction steps (i.e., ensuring enough steps to compute variability through GVI) resulted in a reduced data pool of 105 individuals in the YA group and 81 individuals in the OA group. The characteristics of the study pool and relevant characteristics of sub-groups of participants from each study are presented in Table 2.
Discussion
The GVI was previously developed as a composite measure to quantify the magnitude of variability in spatiotemporal parameters and demonstrated preliminary validity as an indicator of mobility deficits [12]. In the present study, GVI was validated as an indicator of age-related deficits in mobility function. Our study had 4 important findings: (1) GVI was significantly lower in older adults (age ≥ 65 years) compared to younger adults (age < 65 years), (2) decrements in GVI appeared to become
Conclusions
The GVI is a valid assessment for gauging the magnitude of spatiotemporal gait variability in older adults because (1) it is lower in older adults compared to younger, (2) seems to reduce with advancing age during the critical years where mobility deficits begin to emerge, (3) is capable of differentiating older adults who are high-functioning from those with mild to moderate mobility deficits, and (4) associates with some clinical measures of functional mobility and balance performance. Future
Acknowledgements
This study was supported in part by the Brooks Dean's Professorship Award which provided financial assistance for data collection of one of the included studies. Partial support was also provided by the University of Florida Claude D. Pepper Older Americans Independence Center (P30AG028740-04 and 2P30AG028740-06) and by the U.S. Department of Veterans Affairs Rehabilitation Research and Development Service (B7176W and B6793C) for two of other included studies.
Conflict of interest statement:
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