Reliability of COP-based postural sway measures and age-related differences
Introduction
Assessment of human postural (or balance) control is of frequent interest to researchers and clinicians. Decrements in balance control have been considered an important factor in the probability of a fall [1], [2], and falls are often a proximal cause of injury and disability in the general population as well as in contemporary industry [3], [4]. Performance of the balance control system is commonly assessed in the laboratory by quantifying sway during quiet upright stance. The most commonly used measures of sway are various parameters derived from temporal patterns of center of pressure (COP). Traditional COP-based measures (e.g. ellipse area, mean COP velocity, etc.) have demonstrated differences with age [5], [6], sensory conditions [7], and pathology [8], [9], and have been related to risk of falls [1], [2]. However, it has also been suggested that these measures ignore the dynamic characteristics of COP movement and do not represent more subtle aspects of postural control [10]. To overcome these limitations, some modern approaches have been described, including Hurst rescaled range analysis (HR/S) and detrended fluctuation analysis (DFA), which are intended to reveal the underlying fractal properties of the COP time series. Some of these modern methods have been reported as being more sensitive to factors thought to affect balance (e.g. fractal COP measures are more sensitive to age-related changes [11]).
In general, selection of a sway measure for research or clinical use should be motivated by several factors, including the measure reliability. COP mean velocity, for example, has been reported as the most reliable among traditional measures [12], [13], [14], and within-day results appear to have better reliability than between-day results [15]. Despite these valuable studies, important questions remain regarding the reliability of COP-based measures of postural control. No study to our knowledge has investigated the reliability of the HR/S exponent. Only one study assessed within-day reliability of Hurst exponent derived from DFA method and age-related differences [16]. Whether age-related differences in reliability are present for other COP measures remains unknown. In the present study, we assessed within- and between-day reliability of both traditional COP measures and two more recent measures. Results from this work were intended to facilitate better selection of COP-based sway measures in future studies.
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Participants
Thirty-two healthy individuals (16 younger and 16 older, gender balanced in each group) from the University and local community volunteered for the study (Table 1). The two age groups were intended to represent individuals near the typical beginning and end of working life. They had no self-reported injuries, illnesses, musculoskeletal disorders, or occurrences of falls in the past year. All completed an informed consent procedure approved by the Virginia Tech Institutional Review Board.
Procedures
Each
Results
Descriptive summaries of the COP-based measures for both age groups are presented in Table 2. Preliminary MANCOVA results indicated significant effects of age (p < 0.0001) and day (p < 0.0001). There was no significant trial effect (p = 0.41) or day × trial interaction (p = 0.81). Time of day and session interval as covariates also had no significant effects (p = 0.28 and p = 0.12, respectively). Subsequent univariate ANCOVAs indicated significant age effects on all COP measures except for RMS distance (p =
Discussion
The main objective of this study was to assess within- and between-day test–retest reliability of several postural sway measures and to investigate age-related differences in reliability. Overall, the results indicate that COP-based measures have quite diverse levels of reliability. Among the measures obtained, mean velocity was the most reliable, in accordance with previous studies [12], [13], [14]. Using seven healthy and older participants, Lafond et al. [12] reported within-day ICC values
Acknowledgments
This work was supported in part by Cooperative Agreement Number R01 OH0078802 from the Centers for Disease Control and Prevention (CDC). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of CDC. The authors thank Mr. Navrag Singh for his assistance in data collection.
References (37)
- et al.
Ability of static and statistical mechanics posturographic measures to distinguish between age and fall risk
J Biomech
(2005) - et al.
Intrasession reliability of the center of pressure measures of postural steadiness in healthy elderly people
Arch Phys Med Rehabil
(2004) - et al.
Measurement of the visual contribution to postural steadiness from the COP movement: methodology and reliability
Gait Posture
(2005) - et al.
The assessment of body sway and the choice of stability parameter(s)
Gait Posture
(2005) - et al.
Kinematic characteristics of standing disequilibrium: reliability and validity of posturographic protocol
Arch Phys Med Rehabil
(1999) Human balance and posture control during standing and walking
Gait Posture
(1995)- et al.
On the fractal properties of natural human standing
Neurosci Lett
(2000) - et al.
Perturbation of the postural control system induced by muscular fatigue
Gait Posture
(2003) - et al.
Fractal analyses for ‘short’ time series: a re-assessment of classical methods
J Math Psychol
(2006) - et al.
Reliability: What is it, and how is it measured?
Physiotherapy
(2000)
Test–retest reliability of trunk accelerometric gait analysis
Gait Posture
Estimating the reliability of continuous measures with Cronbach's alpha or the intraclass correlation coefficient: toward the integration of two traditions
J Clin Epidemiol
Reliability of traditional and fractal dimension measures of quiet stance center of pressure in young, healthy people
Arch Phys Med Rehabil
Intra-subject inconsistencies in quantitative assessment of body sway
Gait Posture
Adaptation of postural control to perturbations—a process that initiates long-term motor memory
Gait Posture
The relationship of postural sway in standing: the incidence of falls in geriatric subjects
Age Ageing
Aging and postural control: a comparison of spontaneous-and induced-sway balance tests
J Am Geriatr Soc
Antecedent factors and disabling occupational morbidity–insights from the new BLS data
AIHA J
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2022, Physica A: Statistical Mechanics and its ApplicationsCitation Excerpt :We also find that the ICC values for measures 1–7 are typically less than those for measures 8–12. However, the ICC values for measures 1–7 are comparable to those obtained in previous works for other COP-based measures — including measures related to statistical mechanics and nonlinear dynamics [44–48]. In any way, relatively low ICC values in the context of postural sway have been associated to the inherent variability of human balance [48,49].
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2022, Gait and PostureCitation Excerpt :Raw COP displacement data (1200 Hz) were extracted from the Qualisys system and processed using LabVIEW software (version 9.0, National Instruments, USA). The COP signal was low-pass filtered (fourth order Butterworth, zero-phase-lag, 5 Hz cut-off frequency) [16]. For the COP analysis, time series were down sampled by linear interpolation at 100 Hz [17].