Determinants of gait stability while walking on a treadmill: A machine learning approach

Dynamic balance in human locomotion can be assessed through the local dynamic stability (LDS) method. Whereas gait LDS has been used successfully in many settings and applications, little is known about its sensitivity to individual characteristics of healthy adults. Therefore, we reanalyzed a large dataset of accelerometric data measured for 100 healthy adults from 20 to 70 years of age performing 10 min treadmill walking. We sought to assess the extent to which the variations of age, body mass and height, sex, and preferred walking speed (PWS) could influence gait LDS. The random forest (RF) and multiple adaptive regression splines (MARS) algorithms were selected for their good bias-variance tradeoff and their capabilities to handle nonlinear associations. First, through variable importance measure (VIM), we used RF to evaluate which individual characteristics had the highest influence on gait LDS. Second, we used MARS to detect potential interactions among individual characteristics that may influence LDS. The VIM and MARS results indicated that PWS and age correlated with LDS, whereas no associations were found for sex, body height, and body mass. Further, the MARS model detected an age by PWS interaction: on one hand, at high PWS, gait stability is constant across age while, on the other hand, at low PWS, gait instability increases substantially with age. We conclude that it is advisable to consider the participants’ age as well as their PWS to avoid potential biases in evaluating dynamic balance through LDS.     

Circuits for self-motion estimation and walking control in Drosophila

The brain's evolution and operation are inextricably linked to animal movement, and critical functions, such as motor control, spatial perception, and navigation, rely on precise knowledge of body movement. Such internal estimates of self-motion emerge from the integration of mechanosensory and visual feedback with motor-related signals. Thus, this internal representation likely depends on the activity of circuits distributed across the central nervous system. However, the circuits responsible for self-motion estimation, and the exact mechanisms by which motor-sensory coordination occurs within these circuits remain poorly understood. Recent technological advances have positioned Drosophila melanogaster as an advantageous model for investigating the emergence, maintenance, and utilization of self-motion representations during naturalistic walking behaviors. In this review, I will illustrate how the adult fly is providing insights into the fundamental problems of self-motion computations and walking control, which have relevance for all animals.     

Humans control stride-to-stride stepping movements differently for walking and running,independent of speed

As humans walk or run, external (environmental) and internal (physiological) disturbances induce variability. How humans regulate this variability from stride-to-stride can be critical to maintaining balance. One cannot infer what is “controlled” based on analyses of variability alone. Assessing control requires quantifying how deviations are corrected across consecutive movements. Here, we assessed walking and running, each at two speeds. We hypothesized differences in speed would drive changes in variability, while adopting different gaits would drive changes in how people regulated stepping. Ten healthy adults walked/ran on a treadmill under four conditions: walk or run at comfortable speed, and walk or run at their predicted walk-to-run transition speed. Time series of relevant stride parameters were analyzed to quantify variability and stride-to-stride error-correction dynamics within a Goal-Equivalent Manifold (GEM) framework. In all conditions, participants’ stride-to-stride control respected a constant-speed GEM strategy. At each consecutively faster speed, variability tangent to the GEM increased (p ≤ 0.031), while variability perpendicular to the GEM decreased (p ≤ 0.044). There were no differences (p ≥ 0.999) between gaits at the transition speed. Differences in speed determined how stepping variability was structured, independent of gait, confirming our first hypothesis. For running versus walking, measures of GEM-relevant statistical persistence were significantly less (p ≤ 0.004), but showed minimal-to-no speed differences (0.069 ≤ p ≤ 0.718). When running, people corrected deviations both more quickly and more directly, each indicating tighter control. Thus, differences in gait determined how stride-to-stride fluctuations were regulated, independent of speed, confirming our second hypothesis.     

A new measure for upright stability

The control of balance is a primary objective in most human movements. In many cases, research or practice, it is essential to quantitatively know how good the balance is at a body posture or at every moment during a task. In this paper we suggest a new measure for postural upright stability which assigns a value to a body state based on the probability of avoiding a fall initiation from that state. The balance recovery problem is solved for a population sample using a strength database, and the probability of successfully maintaining the balance is found over the population and called the probability of recovery (PoR). It, therefore, describes an attribute of a body state: how possible the control of balance is, or how safe being at that state is. We also show the PoR calculated for a 3-link body model for all states on a plane, compare it to that found using a 2-link model, and compare it to a conventional metric: the margin of stability (MoS). It is shown, for example, that MoS may be very low at a state from which most of the people will be able to easily control their balance.     

The effect of uphill and downhill walking on gait parameters: A self-paced treadmill study

It has been shown that gait parameters vary systematically with the slope of the surface when walking uphill (UH) or downhill (DH) (Andriacchi et al., 1977; Crowe et al., 1996; Kawamura et al., 1991; Kirtley et al., 1985; McIntosh et al., 2006; Sun et al., 1996). However, gait trials performed on inclined surfaces have been subject to certain technical limitations including using fixed speed treadmills (TMs) or, alternatively, sampling only a few gait cycles on inclined ramps. Further, prior work has not analyzed upper body kinematics. This study aims to investigate effects of slope on gait parameters using a self-paced TM (SPTM) which facilitates more natural walking, including measuring upper body kinematics and gait coordination parameters.Gait of 11 young healthy participants was sampled during walking in steady state speed. Measurements were made at slopes of +10°, 0° and −10°. Force plates and a motion capture system were used to reconstruct twenty spatiotemporal gait parameters. For validation, previously described parameters were compared with the literature, and novel parameters measuring upper body kinematics and bilateral gait coordination were also analyzed.Results showed that most lower and upper body gait parameters were affected by walking slope angle. Specifically, UH walking had a higher impact on gait kinematics than DH walking. However, gait coordination parameters were not affected by walking slope, suggesting that gait asymmetry, left-right coordination and gait variability are robust characteristics of walking. The findings of the study are discussed in reference to a potential combined effect of slope and gait speed. Follow-up studies are needed to explore the relative effects of each of these factors.     

Application of principal component analysis in clinical gait research: Identification of systematic differences between healthy and medial knee-osteoarthritic gait

For a successful completion of a movement task the motor control system has to observe a multitude of internal constraints that govern the coordination of its segments. The purpose of this study was to apply principal component (PC) analysis to detect differences in the segmental coordination between healthy subjects and patients with medial knee osteoarthritis (OA). It was hypothesized that (1) systematic differences in patterns of whole body movement would be identifiable with this method even in small sample sized groups and that (2) these differences will include compensatory movements in the OA patients in both the lower and upper body segments. Marker positions and ground reaction forces of three gait trials of 5 healthy and 5 OA participants with full body marker sets were analyzed using a principal component analysis. Group differences in the PC-scores were determined for the first 10 PC-vectors and a linear combination of those PC-vectors where differences were found defined a discriminant vector. Projecting the original trials onto this discriminant vector yielded significant group differences (t(d=8)=3.011; p=0.017) with greater upper body movement in patients with knee OA that was correlated with the medial–lateral ground reaction force. These results help to characterize the adaptation of whole-body gait patterns to knee OA in a relatively small population and may provide an improved basis for the development of interventions to modify knee load. The PC-based motion analysis offered a highly sensitive approach to identify characteristic whole body patterns of movement associated with pathological gait.     

干细胞研究的新途径:miRNAs

微小RNA(microRNAs,miRNAs)是一类内源性的非编码单链RNA,能够通过与靶mRNA特异性的碱基配对而导致靶mRNA降解或抑制其翻译,从而对基因进行转录后调控。干细胞的自我更新和多向分化过程依赖于广泛而多样的调控机制,miRNAs正是这些调控机制中非常重要的一类分子。研究发现,干细胞的自我更新功能需要多种miRNAs的参与来维持;干细胞的分化也是多种miRNAs参与调控的结果。miRNAs可以作为干细胞研究的一个新的切入点。     

Effects of size on Vervet (Cercopithecus aethiops) gait parameters: A cross-sectional approach

A comparison of the values of certain temporal and spatial locomotor parameters was made among ten different-aged (sized) vervet monkeys locomoting at nine identical speeds. Cycle and stance durations decreased across speed for all the animals; at any one speed both parameters also varied directly with body size. Stride length increased with speed for all the animals and was greater in the larger animals. Swing duration and hindlimb support length tended to be relatively consistent for each animal across speed, but varied among the animals directly with body size. Hindlimb duty factor decreased with speed for any one animal but showed no direct correlation with size. Hindlimb angular excursion also showed no correlation with size, nor did it show a simple relationship with speed. In terms of gaits and gait transitions, the data indicate that vervets use a very wide variety of gait types, which are not easily correlated with speed or body size. Furthermore, the data suggest the existence of a run–gallop transition zone of speeds for these animals, rather than the existence of a specific transition speed. Finally, the data were used to test intraspecifically the elastic and dynamic similarity models, both of which predict how locomotor parameters will change with size in animals. The results are generally consistent with the dynamic model.     

Reaction null-space filter: extracting reactionless synergies for optimal postural balance from motion capture data

This paper introduces the notion of a reactionless synergy: a postural variation for a specific motion pattern/strategy, whereby the movements of the segments do not alter the force/moment balance at the feet. Given an optimal initial posture in terms of stability, a reactionless synergy can ensure optimality throughout the entire movement. Reactionless synergies are derived via a dynamical model wherein the feet are regarded to be unfixed. Though in contrast with the conventional fixed-feet models, this approach has the advantage of exhibiting the reactions at the feet explicitly. The dynamical model also facilitates a joint-space decomposition scheme yielding two motion components: the reactionless synergy and an orthogonal complement responsible for the dynamical coupling between the feet and the support. Since the reactionless synergy provides the basis (a feedforward control component) for optimal balance control, it may play an important role when evaluating balance abnormalities or when assessing optimality in balance control. We show how to apply the proposed method for analysis of motion capture data obtained from three voluntary movement patterns in the sagittal plane: squat, sway, and forward bend.     

Modelling the dynamic margins of stability for use in evaluations of balance following a support-surface perturbation

The dynamic margin of stability provides a method that captures the center of mass (CoM) state (position-velocity) in relation to the base of support (BoS). However, the model upon which this concept was derived does not consider how the inertial characteristics of forced support-surface perturbations would influence balance control. Within the current article, the inverted pendulum model was restructured to account for fixed, piecewise accelerations of the BoS. From this logic, two variations of the adjusted margin of stability, each maintaining a similar definition of extrapolated CoM, are proposed; one ignoring horizontal ground contact and inertial forces applied to the BoS, the other incorporating these forces. Unique within the proposed models is the time-variant BoS boundaries that depend on the perturbation applied. Verification of the solution for each model is provided, along with a comparison of obtained values to previous methods of defining CoM position-velocity stability metrics using a computational model and optimal control. For the simpler model variation (ignoring forces), we also assessed how CoM position and perturbation parameter selection over/underestimate the predicted maximal permissible velocity. The results of these analyses suggest that factors which increase the acceleration impulse decrease the difference between the two models; the opposite was observed for factors increasing displacements between the CoM and BoS boundary. Lastly, use of the proposed adjusted margin of stability within an experimental data set highlights the ability of our model to predict instability (stepping strategies; negative margin of stability) relative to the use of the extrapolated CoM alone.     

Role of heel lifting in standing balance recovery: A simulation study

Although lifting the heels has frequently been observed during balance recovery, the function of this movement has generally been overlooked. The present study aimed to investigate the functional role of heel lifting during regaining balance from a perturbed state. Computer simulation was employed to objectively examine the effect of allowing/constraining heel lifting on balance performance. The human model consisted of 3 rigid body segments connected by frictionless joints. Movements were driven by joint torques depending on current joint angle, angular velocity, and activation level. Starting from forward-inclined and static straight-body postures, the optimization goal was to recover balance effectively (so that ground projection of the mass center returned to the inside of the base of support) and efficiently by adjusting ankle and hip joint activation levels. Allowing/constraining heel lifting resulted in virtually identical movements when balance was mildly perturbed at the smallest lean angle (8°). At larger lean angles (8.5° and 9°), heel lifting assisted balance recovery more evidently with larger joint movements. Partial and altered timings of ankle/hip torque activation due to constraining heel lifting reduced linear and angular momentum generation for avoiding forward falling, and resulted in hindered balancing performance.     

The effects of early stages of aging on postural sway: A multiple domain balance assessment using a force platform

Technical advancements in instrumentation and analytical methods have improved the ability of assessing balance control. This study investigated the effects of early stages of aging on postural sway using traditional and contemporary postural indices from different domains. Eleven healthy young adults and fourteen healthy non-faller older adults performed two postural tasks: (a) functional limits of stability and (b) unperturbed bipedal stance for 120 s. Postural indices from spatial, temporal, frequency, and structural domains were extracted from the body’s center of pressure (COP) signals and its Rambling and Trembling components. Results revealed a preservation of functional limits of upright stability in older adults accompanied by larger, faster, and shakier body sway in both anterior-posterior and medio-lateral directions; increased medio-lateral sway frequency; increased irregularity of body sway pattern in time in both directions; and increased area, variability, velocity, and jerkiness of both rambling and trembling components of the COP displacement in the anterior-posterior direction (p < 0.02). Such changes might be interpreted as compensatory adjustments to the age-related decline of sensory, neural, and motor functions. In conclusion, balance assessment using postural indices from different domains extracted from the COP displacement was able to capture subtle effects of the natural process of aging on the mechanisms of postural control. Our findings suggest the use of such indices as potential markers for postural instability and fall risk in older adults.     

A new measure of trip risk integrating minimum foot clearance and dynamic stability across the swing phase of gait

Minimum toe clearance (MTC) is thought to quantify the risk of the toe contacting the ground during the swing phase of gait and initiating a trip, but there are methodological issues with this measure and the risk of trip-related falls has been shown to also be associated with gait speed and dynamic stability. This paper proposes and evaluates a new measure, trip risk integral (TRI), that circumvents many issues with MTC as typically calculated at a single point by considering minimum foot clearance across the entire swing phase and taking into account dynamic stability to estimate risk of falling due to a trip rather than risk of the foot contacting the floor. Shoes and floor surfaces were digitized and MTC and TRI calculated for unimpaired younger (N = 14, age = 26 ± 5), unimpaired older (N = 14, age = 73 ± 7), and older adults who had recently fallen (N = 11, age = 72 ± 5) walking on surfaces with no obstacles, visible obstacles, and hidden obstacles at slow, preferred, and fast gait speeds. MTC and TRI had significant (F ≥ 5, p ≤ 0.005) but differing effects of gait speed and floor surface. As gait speed increased (which increases risk of trip-related falls) MTC indicated less and TRI greater risk, indicating that TRI better quantifies risk of falling due to a trip. While MTC and TRI did not differ by subject group, strong speed-related effects of TRI (F ≥ 8, p ≤ 0.0007) resulted in improved TRI for fallers due to their slower self-selected preferred gait. This demonstrates that slower gait is both an important covariate and potential intervention for trip-related falls.     

Reflex delays of the trunk muscles in response to postural perturbations: A reliability study

It has been reported that altered neuromuscular control of the trunk is associated with lower back pain. In this context reflex delays of the trunk muscles have often been assessed but the reliability of the tests has not been well established. The aim of this study was to test the reliability of measuring reflex delays of the trunk muscles after two types of postural perturbations. 24 Healthy subjects participated in the intra-session study and 13 of them repeated the test protocol within 1–3 weeks, to determine inter-session reliability. Postural reflex delays to unexpected loading and unloading of the arms were assessed in a standing unrestrained position. Each subject performed 40 trials of each test in order to evaluate muscle responses of 5 trunk muscles using surface electromyography. Overall reliability increased with higher number of the averaged trials. Good intra-session (ICC_3,1>0.75) and moderate (ICC_3,1>0.60) inter-session reliability were reached in most of the monitored trunk muscles. Within the performed number of trials we did not observe any significant systematic intra- or inter-session bias effect. Averaging a higher number of consecutive trials would be recommended in future research and clinical practice.     

生态系统途径——生态系统管理的一种新理念

介绍了生态系统途径的概念和内涵．生态系统途径最早由西方生态学家提出。随后得到一系列国际学术组织和国家的认同和支持,其中《生物多样性公约》、世界自然保护联盟和世界野生动物基金发挥了重要作用,．生态系统途径的实质是对土地、水和生物资源进行综合管理,旨在生态系统保护、生物资源可持续利用和共享生物资源三者之间达到平衡．作为生态系统管理的一种方法论,它以生物为核心。将人类及文化的多样性视为生态系统的一个组成部分,2000年《生物多样性公约》缔约国会议上制定的生态系统管理的12条基本原则和5项行动指南,丰富了生态系统途径的内涵,明确了实施的办法,我国在生态系统管理方面有着丰富的学术储备和经验总结。但也存在一定问题。

     

Muscle demand and kinematic similarities between pediatric-modified motor-assisted elliptical training at fast speed and fast overground walking: Real-world implications for pediatric gait rehabilitation

The purpose of this research was to compare children’s lower extremity muscle activity and kinematics while walking at fast pace and training at fast speeds with and without motor-assistance on a pediatric-modified motor-assisted elliptical. Twenty-one children without disabilities were recruited and fifteen completed all three training conditions at self-selected fast pace. Repeated-measures ANOVAs identified muscle demand (peak, mean, duration) differences across device conditions and fast walking. Root mean square error compared overall kinematic profiles and statistical parametric mapping identified kinematic differences between conditions. Motor-assisted training reduced lower extremity muscle demands compared to training without the motor’s assistance (16 of 21 comparisons) and to fast walking (all but one comparison). Training without the motor’s assistance required less muscle effort than fast walking (16 of 21 comparisons). Kinematic differences between device conditions and fast walking were greater distally (thigh, knee, ankle) than proximally (trunk, pelvis, hip). In summary, transitioning from training with to without the motor’s assistance promoted progressively greater activity across the lower extremity muscles studied, with sagittal plane kinematic changes most apparent at the distal joints. Our findings highlight how motor-assistance can be manipulated to customize physiologic challenges to lower extremity muscles prior to fast overground walking.     

A validation study of a new instrument for low cost bite force measurement

Quantitative assessment of force in masticatory muscles is not a routine clinical test, probably due to the lack of an “easy-to-use” device. Aim of this study is (1) to present a low cost bite force instrument located in a custom-made housing, designed to guarantee a comfortable and effective bite action, (2) to evaluate its mechanical characteristics, in order to implement it in clinical settings and in experimental setups.Linearity, repeatability and adaptation over time were assessed on a set of four different sensors in bare and housed condition. Application of the housing to the transducer may appreciably alter the transducer's response. Calibration of the housed transducer is thus necessary in order to correctly record real bite force. This solution may represent a low cost and reliable option for biting force measurement and objective assessment of individual force control in the scientific and clinical setting.     

The use of continuous spectral analysis for the assessment of postural stability changes after sports-related concussion

Impaired postural stability is associated with a variety of pathologies including sports-related concussion (SRC). Quantification of centre of pressure (COP) movement is the most common focus of instrumented assessment. Frequency-domain COP analyses have focused primarily on summary measures or pre-defined frequency bands but continuous analysis may provide novel and complementary insight into pathological control mechanisms. Our aims were (i) to compare post-SRC COP trajectory changes identified using clinician scores (Modified Balance Error Scoring System (M-BESS)), time-domain COP variables and continuous frequency spectral comparison; and (ii) to characterise frequency spectra changes. Male rugby players aged 15–19 years (n = 135) completed a pre-season baseline assessment comprising vision-obscured double-leg, single-leg and tandem stances on a force platform. Participants diagnosed with SRC during the season (n = 15) underwent repeat testing (median 4 days post-SRC; IQR 2.5–6.5). Baseline and post-SRC COP trajectories were compared using common time-domain COP variables, M-BESS scores and continuous frequency spectra. Post-SRC changes were identified using all three approaches. Spectral analysis revealed the largest effect size (Cliff’s delta 0.39) and was the only method to identify differences in all three stances and in double-leg stance. All post-SRC increases in spectral content were in the anteroposterior direction; all decreases were in the mediolateral direction. Changes were localised to higher frequencies (1.7–8 Hz) except for double-leg stance anteroposterior direction, for which increases were observed throughout the analysed range. Our findings suggest that this method of spectral comparison may provide a more responsive and meaningful measure of postural stability changes after SRC than other commonly-used variables.     

A new explicit stability criterion for human periodic breathing<--RID="*"--><--ID="*" This research was supported by grants from DRED (96-920).-->

The aim of this paper is to carry out a stability analysis for periodic breathing in humans that incorporates the dynamic characteristics of ventilation control. A simple CO₂ model that takes into account the main elements of the respiratory system, i.e. the lungs and the ventilatory controller with its dynamic properties, is presented. This model results in a three-dimensional non-linear delay differential system for which there exists a unique equilibrium point. Our stability analysis of this equilibrium point leads to the definition of a new explicit stability criterion and to the demonstration of the existence of a Hopf bifurcation. Numerical simulations illustrate the influence of physiological parameters on the stability of ventilation, and particularly the major role of the dynamic characteristics of the respiratory controller. Received: 2 February 1999 / Revised version: 18 June 1999 / Published online: 23 October 2000