Full length articleReliability and concurrent validity of spatiotemporal stride characteristics measured with an ankle-worn sensor among older individuals
Introduction
Gait characteristics of older people reflect their health status, and deviations from normal gait patterns also predict future adverse health events [1,2]. Spatiotemporal characteristics, such as average stride length, cadence or velocity are often used to describe gait in older populations [3]. Additional insight into the functional status of an individual may be gained by exploring the step-to-step or stride-to-stride variation (gait variability) [3,4], which may be an even more sensitive prognostic indicator of future health outcomes than the mean stride characteristics [5,6].
There are several methods that capture spatiotemporal gait characteristics. Arguably, the golden standards would include motion capture for spatial information (e.g. stride length), and force plates and instrumented walkways for temporal characteristics (e.g. stride duration). However, these are laboratory-bound methods and limit the number of captured strides in overground walking to only the instrumented part/capture volume. Accordingly, much recent effort has been devoted to affordable wearable inertial measurement units (IMU) [[7], [8], [9], [10], [11], [12], [13]], which capture strides independent of a pre-determined capture area [5,6,14,15]. Most of the validation studies of IMU-based gait assessments have been conducted for mean gait characteristics. For example, foot-worn sensors show excellent concurrent validity when compared to motion capture, force plate and instrumented walkways [[7], [8], [9], [10], [11], [12], [13]]. For session-to-session reliability of mean spatiotemporal characteristics, many wear-locations (trunk, shank, foot), have shown good results [7,8,16,17]. However, the concurrent validity and reliability of IMU-based gait variability characterisations have rarely been reported.
IMUs have exhibited the best concurrent validity when foot-worn sensors have been utilised [11,12]. However, mounting a sensor on the foot is somewhat cumbersome particularly if extended monitoring is desired. Participants have indicated a preference for an ankle worn device if given a choice [18]. Hip-worn sensors, while convenient, produce suboptimal results, particularly when attempting to identify stride length or gait velocity [19] and therefore, an ankle/shank-worn unit might be considered the preferred wear-location. While the validity and reliability of ankle/shank-worn IMUs for spatiotemporal gait characteristics assessments have been established among young healthy adults [11,12], data among older people is still missing. This is problematic because older people walk slower than younger people [20], and the validity and reliability of some IMU-based gait characteristics depend on gait speed [7]. Consequently, the validity and reliability of IMUs should be evaluated also among older people.
The purpose of the present study was to assess the concurrent validity and session-to-session reliability of ankle-worn IMU-based spatiotemporal gait characteristic assessments among healthy older adults aged 70 years and older. Numerous alternatives for gait event identification have been reported in the literature but no golden standard algorithm has yet emerged. Therefore, a novel algorithm based on prior art [21] was developed and evaluated in the present study.
Section snippets
Methods
A convenience sample of N = 27 healthy men (N = 10) and women (N = 17) were recruited from the University of the Third Age meetings at the University of Jyväskylä, and through word of mouth. The mean age, height and body mass of the women were 74.8 (SD 44) years, 160 (6) cm, and 68.8 (9.5) kg, and the respective values for men were 73.7 (4.1) years, 176 (7) cm, and 84.2 (9.4) kg. The inclusion criteria included age 70 years or older, and the ability to walk continuously for three minutes
Results
The mean values of the stride characteristics measured with both the motion capture-based and IMU-based methods and on both measurement sessions are given in Table 1.
Significant difference (mean bias calculated as motion capture minus IMU) was observed between methods in stride length (3 cm), stride velocity (2 cm/s), stance duration SD (-4.5 ms), swing duration SD (-10.7 ms), stride length SD (-3.1 cm), and stride velocity SD (-2.4 cm/s) (all p < 0.05). Fair to excellent agreement was observed
Discussion
The primary findings of the present study were 1) that, apart from swing duration, IMU-evaluated mean stride characteristics exhibited excellent concurrent validity to corresponding motion-capture-evaluated values and 2) that both methods exhibited excellent reliability for mean stride characteristics. However, IMU-based stride variability characteristics exhibited poor concurrent validity to motion capture. Notably, both the motion capture and the IMU-based characterisation exhibited poor to
Declaration of Competing Interest
None of the authors have conflicts of interests to report.
Acknowledgements
We wish to thank the participants who volunteered their time. Gerontology Research Center is a joint effort between the University of Jyvaskyla and the University of Tampere.
This work was supported by the European Research Council (grant number 693045, Prof. Rantanen) and the Academy of Finland (grant number 310526, Prof. Rantanen).
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