Speeding up or slowing down?: Gait adaptations to preserve gait stability in response to balance perturbations (original) (raw)
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During human walking, perturbations to the upper body can be partly corrected by placing the foot appropriately on the next step. Here, we infer aspects of such foot placement dynamics using step-to-step variability over hundreds of steps of steady-state walking data. In particular, we infer dependence of the 'next' foot position on upper body state at different phases during the 'current' step. We show that a linear function of the hip position and velocity state (approximating the body center of mass state) during mid-stance explains over 80% of the next lateral foot position variance, consistent with (but not proving) lateral stabilization using foot placement. This linear function implies that a rightward pelvic deviation during a left stance results in a larger step width and smaller step length than average on the next foot placement. The absolute position on the treadmill does not add significant information about the next foot relative to current stance foot over that already available in the pelvis position and velocity. Such walking dynamics inference with steady-state data may allow diagnostics of stability and inform biomimetic exoskeleton or robot design.
A Simple Model of Stability Limits Applied to Sidestepping in Young, Elderly and Elderly Fallers
2006
Impaired lateral balance involving the frontal plane is particularly relevant to the problem of falls with aging. Protective stepping is critical to avoiding falling, and medio-lateral (M-L) stepping involves two quite complicated action choices - lateral side step and crossover stepping. The aims of this study were to identify differences in movement patterns between young healthy subjects and elderly fallers and non-fallers (determined prospectively over a year), and to identify performance differences for the two types of stepping response. Our tool for these evaluations was a computational model of the center of mass as a pendulum, which identifies the limits of stability beyond which additional steps are required. In response to multi-directional stepper-motor induced waist-pull perturbations of standing balance, the older groups took multiple steps more often than the young (55% compared to 9% of the trials), and the largest differences were seen in the pulls to the side. On these side pulls, crossover stepping and limb collisions increased with age and prospectively determined fall risk. Consequently the model analysis focused only on the most problematic lateral pulls, and only on pulls to the right. In both stepping off and landing, the young most closely approached the stability limits predicted by the model, followed by the older non-fallers and then fallers. In crossover stepping, all groups landed closer to their limits when multiple steps occurred, though older fallers were closest to instability. These findings revealed distinctive age differences related to fall risk and shed light on such modeling approaches for understanding the reasons why older fallers may select stepping responses and the effectiveness of such responses in recovering balance
Journal of Aging and Health, 2007
Purpose: The purpose was to identify differences in gait characteristics between older fallers with a tendency to fall sideways compared to those who do not fall to the side. Method: The authors conducted a prospective, case control study of ambulatory adults older than 70 residing in retirement communities. Measurements included spatial and temporal gait parameters and prospective fall surveillance. Results: In all, 29 participants fell to the side, and 64 fell in other directions (forward, backward, straight down); 46 participants experienced no falls. Side-fallers exhibited narrower stride widths compared to other-directed fallers, and stepwise and discriminant analysis correctly classified 67% of side-fallers and other-directed fallers using only stride width. Discussion: This study suggests that side-fallers, who have narrower stride widths compared to those who fall in other directions, may not be adapting their gait to compensate for lateral instability. More research is need...
Assessing the stability of human locomotion: a review of current measures
Journal of The Royal Society Interface, 2013
Falling poses a major threat to the steadily growing population of the elderly in modern-day society. A major challenge in the prevention of falls is the identification of individuals who are at risk of falling owing to an unstable gait. At present, several methods are available for estimating gait stability, each with its own advantages and disadvantages. In this paper, we review the currently available measures: the maximum Lyapunov exponent (l S and l L ), the maximum Floquet multiplier, variability measures, long-range correlations, extrapolated centre of mass, stabilizing and destabilizing forces, foot placement estimator, gait sensitivity norm and maximum allowableperturbation. We explain what these measures represent and how they are calculated, and we assess their validity, divided up into construct validity, predictive validity in simple models, convergent validity in experimental studies, and predictive validity in observational studies. We conclude that (i) the validity of variability measures and l S is best supported across all levels, (ii) the maximum Floquet multiplier and l L have good construct validity, but negative predictive validity in models, negative convergent validity and (for l L ) negative predictive validity in observational studies, (iii) long-range correlations lack construct validity and predictive validity in models and have negative convergent validity, and (iv) measures derived from perturbation experiments have good construct validity, but data are lacking on convergent validity in experimental studies and predictive validity in observational studies. In closing, directions for future research on dynamic gait stability are discussed.
Gait & Posture, 2018
A B S T R A C T Background: Older adults are at an exceptionally high risk of falls, and most falls occur during locomotor activities such as walking. Reduced local dynamic stability in old age is often interpreted to suggest a lessened capacity to respond to more significant balance challenges encountered during walking and future falls risk. However, it remains unclear whether local dynamic stability during normal, unperturbed walking predicts the response to larger external balance disturbances. Research question: We tested the hypothesis that larger values of local dynamic instability during unperturbed walking would positively correlate with larger changes thereof due to optical flow balance perturbations. Methods: We used trunk kinematics collected in subjects across a spectrum of walking balance integrity – young adults, older non-fallers, and older fallers – during walking with and without mediolateral optical flow perturbations of four different amplitudes. Results: We first found evidence that optical flow perturbations of sufficient amplitude appear capable of revealing independent effects of aging and falls history that are not otherwise apparent during normal, un-perturbed walking. We also reject our primary hypothesis; a significant negative correlation only in young adults indicated that individuals with more local dynamic instability during normal, unperturbed walking exhibited smaller responses to optical flow perturbations. In contrast, most prominently in older fallers, the response to optical flow perturbations appeared independent of their baseline level of dynamic instability. Significance: We propose that predicting the response to balance perturbations in older fallers, at least that measured using local dynamic stability, likely requires measuring that response directly.
Are the Spatio temporal Parameters of Gait Capable of Distinguishing Faller
EDIZIONI MINERVA MEDICA, 2014
Fall is a common and a major cause of injuries. It is important to find elderlies who are prone to falls. The majority of serious falls occur during walking among the older adults. Analyzing the spatio-temporal parameters of walking is an easy way of assessment in the clinical setting, but is it capable of distinguishing a faller from a non-faller elderly? Through a systematic review of the literature, the objective of this systematic review was to identify and summarize the differences in the, spatio-temporal parameters of walking in elderly,falters and non-fallers and to find out if these parameters are capable of distinguishing a faller from non-faller. All original research articles which compared any special or temporal walking parameters in faller and non-faller elderlies were systematically searched within the Scopus and Embase databases., Effect size analysis was also done to standardize findings and compare the gait parameters of fallers and,non-fillerS across the selected studies. The electronic search led to 5381 articles. After title and abstract screening 30 articles were chosen; further assessment of the full texts led to 17 eligible articles for inclusion in the review It seems that temporal measurements are more sensitive to the detection of risk of fall in elderly people; The results of the 17 selected studies, showed that failers have a tendency toward a Slower walking speed and cadence, longer stride time, and double support duration. Also, fallers showed shorter stride and step length, wider step width and more variability in spatio-temporal parameters of gait. According to the effect size analysis, step length, gait speed, stride length and stance time variability were respectively more capable of differentiating faller from non-faller elderlies. However, because of the difference of methodology and number of studies which investigated each parameter, these results are prone to imprecision. Spatio-temporal analysis of level walking is not sufficient and cannot act as a reliable predictor of stalls in elderly individuals.
Dynamic stability differences in fall-prone and healthy adults
Journal of Electromyography and Kinesiology, 2008
Typical stability assessments characterize performance in standing balance despite the fact that most falls occur during dynamic activities such as walking. The objective of this study was to identify dynamic stability differences between fall-prone elderly individuals, healthy age-matched adults, and young adults. Three-dimensional video-motion analysis kinematic data were recorded for 35 contiguous steps while subjects walked on a treadmill at three speeds. From this data, we estimated the vector from the center-of-mass to the center of pressure at each foot-strike. Dynamic stability of walking was computed by methods of Poincare analyses of these vectors. Results revealed that the fall-prone group demonstrated poorer dynamic stability than the healthy elderly and young adult groups. Stability was not influenced by walking velocity, indicating that group differences in walking speed could not fully explain the differences in stability. This pilot study supports the need for future investigations using larger population samples to study fall-prone individuals using nonlinear dynamic analyses of movement kinematics.
Are gait variability and stability measures influenced by directional changes?
BioMedical Engineering OnLine, 2014
Background: Many gait variability and stability measures have been proposed in the literature, with the aim to quantify gait impairment, degree of neuro-motor control and balance disorders in healthy and pathological subjects. These measures are often obtained from lower trunk acceleration data, typically acquired during rectilinear gait, but relevant experimental protocols and data processing techniques lack in standardization. Since directional changes represent an essential aspect of gait, the assessment of their influence on such measures is essential for standardization. In addition, their investigation is needed to evaluate the applicability of these measures in laboratory trials and in daily life activity analysis. A further methodological aspect to be standardized concerns the assessment of the sampling frequency, which could affect stability measures. The aim of the present study was hence to assess if gait variability and stability measures are affected by directional changes, and to evaluate the influence of sampling frequency of trunk acceleration data on the results. Methods: Fifty-one healthy young adults performed a 6-minute walk test along a 30 m straight pathway, turning by 180 deg at each end of the pathway. Nine variability and stability measures (Standard deviation, Coefficient of variation, Poincaré plots, maximum Floquet multipliers, short-term Lyapunov exponents, Recurrence quantification analysis, Multiscale entropy, Harmonic ratio and Index of harmonicity) were calculated on stride duration and trunk acceleration data (acquired at 100 Hz and 200 Hz) coming from straight walking windows and from windows including both straight walking and the directional change. Results: Harmonic ratio was the only measure that resulted to be affected by directional changes and sampling frequency, decreasing with the presence of a directional change task. HR was affected in the AP and V directions for the 200 Hz, but only in AP direction for the 100 Hz group. Conclusion: Multiscale entropy, short term Lyapunov exponents and Recurrence quantification analysis were generally not affected by directional changes nor by sampling frequency, and could contribute to the definition of a fall risk index in free-walking conditions.
Minimum foot clearance during walking: Strategies for the minimisation of trip-related falls
Gait & Posture, 2007
This paper models minimum foot clearance (MFC) data during steady-state gait to investigate how the various descriptive statistics of the MFC distribution differ in healthy young and elderly females. A minimum of 20 min of treadmill walking was analysed for 17 young and 16 elderly females using a Peak Motus motion analysis system. The results indicated that none of the 33 participants' MFC data sets were Normally distributed. The deviation from a Normal distribution was systematic (always skewness > 0 and kurtosis > 0). Skewness and kurtosis in MFC data was highly correlated (young: r = 0.60, p = 0.01; elderly: r = 0.95, p < 0.01). MFC descriptive statistics provide useful information about basic strategies used by individuals to minimize the likelihood of tripping. Possible strategies to minimize tripping include: (a) increasing MFC height central tendency, (b) reducing MFC variability, and/or (c) increasing right skewness. A low median MFC was often associated with a low IQR or high skewness to compensate. Further research is required to establish how, or if at all, these strategies are modified in populations that are more at risk of falling. #