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Identification of the period of stability in a balance test after stepping up using a simplified cumulative sumFalls are a major cause of death in older people. One method used to predict falls is analysis of Centre of Pressure (CoP) displacement, which provides a measure of balance quality. The Balance Quality Tester (BQT) is a device based on a commercial bathroom scale that calculates instantaneous values of vertical ground reaction force (Fz) as well as the CoP in both anteroposterior (AP) and mediolateral (ML) directions. The entire testing process needs to take no longer than 12 s to ensure subject compliance, making it vital that calculations related to balance are only calculated for the period when the subject is static. In the present study, a method is presented to detect the stabilization period after a subject has stepped onto the BQT. Four different phases of the test are identified (stepping-on, stabilization, balancing, stepping-off), ensuring that subjects are static when parameters from the balancing phase are calculated. The method, based on a simplified cumulative sum (CUSUM) algorithm, could detect the change between unstable and stable stance. The time taken to stabilize significantly affected the static balance variables of surface area and trajectory velocity, and was also related to Timed-up-and-Go performance. Such a finding suggests that the time to stabilize could be a worthwhile parameter to explore as a potential indicator of balance problems and fall risk in older people.
Modified bathroom scale and balance assessment: a comparison with clinical testsFrailty and detection of fall risk are major issues in preventive gerontology. A simple tool frequently used in daily life, a bathroom scale (balance quality tester: BQT), was modified to obtain information on the balance of 84 outpatients consulting at a geriatric clinic. The results computed from the BQT were compared to the values of three geriatric tests that are widely used either to detect a fall risk or frailty (timed get up and go: TUG; 10 m walking speed: WS; walking time: WT; one-leg stand: OS). The BQT calculates four parameters that are then scored and weighted, thus creating an overall indicator of balance quality. Raw data, partial scores and the global score were compared with the results of the three geriatric tests. The WT values had the highest correlation with BQT raw data (r = 0.55), while TUG (r = 0.53) and WS (r = 0.56) had the highest correlation with BQT partial scores. ROC curves for OS cut-off values (4 and 5 s) were produced, with the best results obtained for a 5 s cut-off, both with the partial scores combined using Fisher's combination (specificity 85 %: <0.11, sensitivity 85 %: >0.48), and with the empirical score (specificity 85 %: <7, sensitivity 85 %: >8). A BQT empirical score of less than seven can detect fall risk in a community dwelling population.
Reconstructed phase spaces of intrinsic mode functions : application to postural stability analysisIn this contribution, we propose an efficient nonlinear analysis method characterizing postural steadiness. The analyzed signal is the displacement of the centre of pressure (COP) collected from a force plate used for measuring postural sway. The proposed method consists of analyzing the nonlinear dynamics of the intrinsic mode functions (IMF) of the COP signal. The nonlinear properties are assessed through the reconstructed phase spaces of the different IMFs. This study shows some specific geometries of the attractors of some intrinsic modes. Moreover, the volume spanned by the geometric attractors in the reconstructed phase space represents an efficient indicator of the postural stability of the subject. Experiments results corroborate the effectiveness of the method to blindly discriminate young subjects, elderly subjects and subjects presenting a risk of falling.
Stepping down backwards as a means of detecting biomechanical differences between healthy older and younger adultsChanges in sensory- motor systems that occur with age result in a decrease in postural equilibrium, which has been linked with an increased risk of falling in the elderly. Stepping down backwards from a step perturbs dynamic postural equilibrium, thus offering an opportunity to analyze the biomechanical parameters underlying the control of balance. The aim of this study was to analyze modifications in motor patterns used by older adult subjects to control equilibrium under the environmental constraint of a backward stepping-down movement. Ten healthy young adult and 10 healthy older adult subjects with no previous history of falls stepped down backward from a stable position on a force plate 7 cm high, at a spontaneous velocity. Each subject performed five trials, and the mean of all trials was used for subsequent analyses. An ANOVA was performed, with temporal parameters defining the phases of the stepping-down backward movement, center of mass velocity, vertical ground reaction force, impulse, and slope as dependent variables, and subject group as independent variable. Older adult subjects had a longer total movement duration, a longer phase of anticipatory postural adjustments, and a longer weight-transfer phase than young adult subjects (p<0.05). In contrast, older adults had a shorter relative swing phase than the young adults (p<0.05) and a lower center of mass velocity, impulse and slope (p<0.05) than young adults. To counterbalance the perturbation of postural equilibrium created by the backward stepping-down movement, older adults decreased the intensity of ground reaction forces and spent correspondingly more time in double-support phases than young adults. BACKGROUND AND AIMS METHODS RESULTS CONCLUSIONS