scholarly journals Small Directional Treadmill Perturbations Induce Differential Gait Stability Adaptation

2021 ◽  
Author(s):  
Jinfeng Li ◽  
Helen J. Huang
Keyword(s):  
Center Of Mass ◽  
Lateral Shift ◽  
Small Magnitude ◽  
Small Perturbations ◽  
Gait Stability ◽  
Foot Placement ◽  
Margin Of Stability ◽  
Belt Speed ◽  
Base Of Support ◽  
Anterior Posterior

Introducing unexpected perturbations to challenge gait stability is an effective approach to investigate balance control strategies. Little is known about the extent to which people can respond to small perturbations during walking. This study aimed to determine how subjects adapted gait stability to multidirectional perturbations with small magnitudes applied on a stride-by-stride basis. Ten healthy young subjects walked on a treadmill that either briefly decelerated belt speed ("stick"), accelerated belt speed ("slip"), or shifted the platform medial-laterally at right leg mid-stance. We quantified gait stability adaptation in both anterior-posterior and medial-lateral directions using margin of stability and its components, base of support and extrapolated center of mass. Gait stability was disrupted upon initially experiencing the small perturbations as margin of stability decreased in the stick, slip, and medial shift perturbations and increased in the lateral shift perturbation. Gait stability metrics were generally disrupted more for perturbations in the coincident direction. As subjects adapted their margin of stability using feedback strategies in response to the small perturbations, subjects primarily used base of support (foot placement) control in the stick and lateral shift perturbations and extrapolated center of mass control in the slip and medial shift perturbations. Gait stability metrics adapted to perturbations in both anterior-posterior and medial-lateral directions. These findings provide new knowledge about the extent of gait stability adaptation to small magnitude perturbations applied on a stride-by-stride basis and reveal potential new approaches for balance training interventions to target foot placement and center of mass control.

scholarly journals Small Directional Treadmill Perturbations Induce Differential Gait Stability Adaptation

2021 ◽  
Author(s):  
Jinfeng Li ◽  
Helen J. Huang
Keyword(s):  
Center Of Mass ◽  
Lateral Shift ◽  
Stick Slip ◽  
Small Magnitude ◽  
Small Perturbations ◽  
Gait Stability ◽  
Foot Placement ◽  
Margin Of Stability ◽  
Belt Speed ◽  
Base Of Support

Introducing unexpected perturbations to challenge gait stability is an effective approach to investigate balance control strategies. Little is known about the extent to which people can respond to small perturbations during walking. This study aimed to determine how subjects adapted gait stability to multidirectional perturbations with small magnitudes applied on a stride-by-stride basis. Ten healthy young subjects walked on a treadmill that either briefly decelerated belt speed ("stick"), accelerated belt speed ("slip"), or shifted the platform medial-laterally at right leg mid-stance. We quantified gait stability adaptation in both anterior-posterior and medial-lateral directions using margin of stability and its components, base of support and extrapolated center of mass. Gait stability was disrupted upon initially experiencing the small perturbations as margin of stability decreased in the stick, slip, and medial shift perturbations and increased in the lateral shift perturbation. Gait stability metrics were generally disrupted more for perturbations in the coincident direction. Subjects employed both feedback and feedforward strategies in response to the small perturbations, but mostly used feedback strategies during adaptation. Subjects primarily used base of support (foot placement) control in the lateral shift perturbation and extrapolated center of mass control in the slip and medial shift perturbations. These findings provide new knowledge about the extent of gait stability adaptation to small magnitude perturbations applied on a stride-by-stride basis and reveal potential new approaches for balance training interventions to target foot placement and center of mass control.

scholarly journals Rethinking Margin of Stability: Incorporating Step-To-Step Regulation to Resolve the Paradox

2021 ◽  
Author(s):  
Meghan Kazanski ◽  
Joseph P. Cusumano ◽  
Jonathan B. Dingwell
Keyword(s):  
Inverted Pendulum ◽  
Balance Control ◽  
Center Of Mass ◽  
Frontal Plane ◽  
Lateral Instability ◽  
Foot Placement ◽  
Margin Of Stability ◽  
Increased Risk ◽  
Mediolateral Stability ◽  
Balance Dynamics

ABSTRACTMaintaining frontal-plane stability is a major objective of human walking. Derived from inverted pendulum dynamics, the mediolateral Margin of Stability (MoSML) is frequently used to measure people’s frontal-plane stability on average. However, typical MoSML-based analyses deliver paradoxical interpretations of stability status. To address mediolateral stability using MoSML, we must first resolve this paradox. Here, we developed a novel framework that unifies the well-established inverted pendulum model with Goal-Equivalent Manifold (GEM)-based analyses to assess how humans regulate step-to-step balance dynamics to maintain mediolateral stability. We quantified the extent to which people corrected fluctuations in mediolateral center-of-mass state relative to a MoSML-defined candidate stability GEM in the inverted pendulum phase plane. Participants’ variability and step-to-step correction of tangent and perpendicular deviations from the candidate stability GEM demonstrate that regulation of balance dynamics involves more than simply trying to execute a constant-MoSML balance control strategy. Participants adapted these step-to-step corrections to mediolateral sensory and mechanical perturbations. How participants regulated mediolateral foot placement strongly predicted how they regulated center-of-mass state fluctuations, suggesting that regulation of center-of-mass state occurs as a biomechanical consequence of foot placement regulation. We introduce the Probability of Instability (PoI), a convenient statistic that accounts for step-to-step variance to properly predict instability likelihood on any given future step. Participants increased lateral PoI when destabilized, as expected. These lateral PoI indicated an increased risk of lateral instability, despite larger (i.e., more stable) average MoSML. PoI thereby explicitly predicts instability risk to decisively resolve the existing paradox that arises from conventional MoSML implementations.

Validating Determinants for an Alternate Foot Placement Selection Algorithm During Human Locomotion in Cluttered Terrain

2007 ◽  
Vol 98 (4) ◽  
pp. 1928-1940 ◽  
Author(s):  
Renato Moraes ◽  
Fran Allard ◽  
Aftab E. Patla
Keyword(s):  
Dynamic Stability ◽  
Center Of Mass ◽  
Frontal Plane ◽  
Human Locomotion ◽  
The Body ◽  
Selection Algorithm ◽  
Foot Placement ◽  
Double Support ◽  
One Step ◽  
Base Of Support

The goal of this study was to validate dynamic stability and forward progression determinants for the alternate foot placement selection algorithm. Participants were asked to walk on level ground and avoid stepping, when present, on a virtual white planar obstacle. They had a one-step duration to select an alternate foot placement, with the task performed under two conditions: free (participants chose the alternate foot placement that was appropriate) and forced (a green arrow projected over the white planar obstacle cued the alternate foot placement). To validate the dynamic stability determinant, the distance between the extrapolated center of mass (COM) position, which incorporates the dynamics of the body, and the limits of the base of support was calculated in both anteroposterior (AP) and mediolateral (ML) directions in the double support phase. To address the second determinant, COM deviation from straight ahead was measured between adaptive and subsequent steps. The results of this study showed that long and lateral choices were dominant in the free condition, and these adjustments did not compromise stability in both adaptive and subsequent steps compared with the short and medial adjustments, which were infrequent and adversely affected stability. Therefore stability is critical when selecting an alternate foot placement in a cluttered terrain. In addition, changes in the plane of progression resulted in small deviations of COM from the endpoint goal. Forward progression of COM was maintained even for foot placement changes in the frontal plane, validating this determinant as part of the selection algorithm.

scholarly journals The critical phase for visual control of human walking over complex terrain

2017 ◽  
Vol 114 (32) ◽  
pp. E6720-E6729 ◽  
Author(s):  
Jonathan Samir Matthis ◽  
Sean L. Barton ◽  
Brett R. Fajen
Keyword(s):  
Complex Terrain ◽  
Visual Information ◽  
Center Of Mass ◽  
Ground Surface ◽  
The Body ◽  
Foot Placement ◽  
Preceding Step ◽  
Control Work ◽  
Base Of Support ◽  
Target Visibility

To walk efficiently over complex terrain, humans must use vision to tailor their gait to the upcoming ground surface without interfering with the exploitation of passive mechanical forces. We propose that walkers use visual information to initialize the mechanical state of the body before the beginning of each step so the resulting ballistic trajectory of the walker’s center-of-mass will facilitate stepping on target footholds. Using a precision stepping task and synchronizing target visibility to the gait cycle, we empirically validated two predictions derived from this strategy: (1) Walkers must have information about upcoming footholds during the second half of the preceding step, and (2) foot placement is guided by information about the position of the target foothold relative to the preceding base of support. We conclude that active and passive modes of control work synergistically to allow walkers to negotiate complex terrain with efficiency, stability, and precision.

scholarly journals A novel Movement Amplification environment reveals effects of controlling lateral centre of mass motion on gait stability and metabolic cost

2020 ◽  
Vol 7 (1) ◽  
pp. 190889
Author(s):  
Mengnan/Mary Wu ◽  
Geoffrey L. Brown ◽  
Jane L. Woodward ◽  
Sjoerd M. Bruijn ◽  
Keith E. Gordon
Keyword(s):  
Metabolic Cost ◽  
Mass Motion ◽  
Step Width ◽  
Centre Of Mass ◽  
Cost Of Transport ◽  
Gait Patterns ◽  
Gait Stability ◽  
Foot Placement ◽  
Base Of Support ◽  
Healthy Participants

During human walking, the centre of mass (COM) laterally oscillates, regularly transitioning its position above the two alternating support limbs. To maintain upright forward-directed walking, lateral COM excursion should remain within the base of support, on average. As necessary, humans can modify COM motion through various methods, including foot placement. How the nervous system controls these oscillations and the costs associated with control are not fully understood. To examine how lateral COM motions are controlled, healthy participants walked in a ‘Movement Amplification’ force field that increased lateral COM momentum in a manner dependent on the participant's own motion (forces were applied to the pelvis proportional to and in the same direction as lateral COM velocity). We hypothesized that metabolic cost to control lateral COM motion would increase with the gain of the field. In the Movement Amplification field, participants were significantly less stable than during baseline walking. Stability significantly decreased as the field gain increased. Participants also modified gait patterns, including increasing step width, which increased the metabolic cost of transport as the field gain increased. These results support previous research suggesting that humans modulate foot placement to control lateral COM motion, incurring a metabolic cost.

scholarly journals Effects of vestibular stimulation on gait stability and variability

2021 ◽  
Author(s):  
Rina M. Magnani ◽  
Jaap H. van Dieën ◽  
Sjoerd M. Bruijn
Keyword(s):  
Muscle Activity ◽  
Center Of Mass ◽  
Mass Movement ◽  
Stable Condition ◽  
Vestibular Stimulation ◽  
Step Width ◽  
Gait Stability ◽  
Foot Placement ◽  
Vestibular Information ◽  
Narrow Base

AbstractVestibular information modulates muscle activity during gait, presumably to contribute stability, because noisy electrical vestibular stimulation perturbs gait stability. An important mechanism to stabilize gait in the mediolateral direction is to coordinate foot placement based on a sensory estimate of the trunk center of mass state, to which vestibular information appears to contribute. We, therefore expected that noisy vestibular stimulation would decrease the correlation between foot placement and trunk center of mass state. Moreover, as vestibular modulation of muscle activity during gait depends on step width, we expected stronger effects for narrow-base than normal walking, and smaller effects for wide-base walking. In eleven healthy subjects we measured the kinematics of the trunk (as a proxy of the center of mass), and feet, while they walked on a treadmill in six conditions, including three different step widths: control (preferred step width), narrow-base (steps smaller than hip width), and wide-base (with steps greater than hip width). The three conditions were conducted with and without a bipolar electrical stimulus, applied behind the ears (5 mA). Walking with EVS reduced gait stability but increased the foot placement to center of mass correlation in different step width conditions. The narrow-base walking was the most stable condition and showed a stronger correlation between foot placement and center of mass state. We argue that EVS destabilized gait, but that this was partially compensated for by tightened control over foot placement, which would require successful use of other than vestibular sensory inputs, to estimate center of mass movement.

scholarly journals Ambulatory Assessment of the Dynamic Margin of Stability Using an Inertial Sensor Network

Sensors ◽  
2019 ◽  
Vol 19 (19) ◽  
pp. 4117 ◽  
Author(s):  
Michelangelo Guaitolini ◽  
Federica Aprigliano ◽  
Andrea Mannini ◽  
Silvestro Micera ◽  
Vito Monaco ◽  
...  
Keyword(s):  
Balance Control ◽  
Inertial Sensor ◽  
Center Of Mass ◽  
The Body ◽  
Lower Limbs ◽  
Measurement Unit ◽  
Margin Of Stability ◽  
Walking Velocity ◽  
Body Center ◽  
Base Of Support

Loss of stability is a precursor to falling and therefore represents a leading cause of injury, especially in fragile people. Thus, dynamic stability during activities of daily living (ADLs) needs to be considered to assess balance control and fall risk. The dynamic margin of stability (MOS) is often used as an indicator of how the body center of mass is located and moves relative to the base of support. In this work, we propose a magneto-inertial measurement unit (MIMU)-based method to assess the MOS of a gait. Six young healthy subjects were asked to walk on a treadmill at different velocities while wearing MIMUs on their lower limbs and pelvis. We then assessed the MOS by computing the lower body displacement with respect to the leading inverse kinematics approach. The results were compared with those obtained using a camera-based system in terms of root mean square deviation (RMSD) and correlation coefficient (ρ). We obtained a RMSD of ≤1.80 cm and ρ ≥ 0.85 for each walking velocity. The findings revealed that our method is comparable to camera-based systems in terms of accuracy, suggesting that it may represent a strategy to assess stability during ADLs in unstructured environments.

Volume change of the ocular lens during accommodation

2007 ◽  
Vol 293 (2) ◽  
pp. C797-C804 ◽  
Author(s):  
R. Gerometta ◽  
A. C. Zamudio ◽  
D. P. Escobar ◽  
O. A. Candia
Keyword(s):  
Structural Parameters ◽  
Center Of Mass ◽  
Physiological Solution ◽  
Volume Determination ◽  
Cross Sectional ◽  
Lens Fibers ◽  
Human Lenses ◽  
Lens Surface ◽  
Shape Changes ◽  
Anterior Posterior

During accommodation, mammalian lenses change shape from a rounder configuration (near focusing) to a flatter one (distance focusing). Thus the lens must have the capacity to change its volume, capsular surface area, or both. Because lens topology is similar to a torus, we developed an approach that allows volume determination from the lens cross-sectional area (CSA). The CSA was obtained from photographs taken perpendicularly to the lenticular anterior-posterior (A-P) axis and computed with software. We calculated the volume of isolated bovine lenses in conditions simulating accommodation by forcing shape changes with a custom-built stretching device in which the ciliary body-zonulae-lens complex (CB-Z-L) was placed. Two measurements were taken (CSA and center of mass) to calculate volume. Mechanically stretching the CB-Z-L increased the equatorial length and decreased the A-P length, CSA, and lens volume. The control parameters were restored when the lenses were stretched and relaxed in an aqueous physiological solution, but not when submerged in oil, a condition with which fluid leaves the lens and does not reenter. This suggests that changes in lens CSA previously observed in humans could have resulted from fluid movement out of the lens. Thus accommodation may involve changes not only in capsular surface but also in volume. Furthermore, we calculated theoretical volume changes during accommodation in models of human lenses using published structural parameters. In conclusion, we suggest that impediments to fluid flow between the aquaporin-rich lens fibers and the lens surface could contribute to the aging-related loss of accommodative power.

Capturability of Inverted Pendulum Gait Model Under Slip Conditions

2018 ◽  
Author(s):  
Marko Mihalec ◽  
Jingang Yi
Keyword(s):  
Reaction Time ◽  
Coefficient Of Friction ◽  
Inverted Pendulum ◽  
Center Of Mass ◽  
Control Input ◽  
Vertical Movements ◽  
Foot Placement ◽  
Slip Conditions ◽  
The Coefficient Of Friction ◽  
Stable Gait

This paper presents a simple inverted pendulum gait model to study walking under slip conditions. The model allows for both the horizontal and vertical movements of the center of mass during normal walking and walking gaits with foot slip. Stability of the system is analyzed using the concept of capturability. Considering foot placement as a control input, we obtain the stable regions which lead to stable gait. The size of those stable regions is used to evaluate the effect of the coefficient of friction and the slip reaction time on capturability. We also analyze the feasibility of recovery from slip gait in relation to the coefficient of friction and the reaction time. The results confirm the effectiveness of the model and the capturability developement.

Dynamic and Reactive Walking for Humanoid Robots Based on Foot Placement Control

2016 ◽  
Vol 13 (02) ◽  
pp. 1550041 ◽  
Author(s):  
Juan Alejandro Castano ◽  
Zhibin Li ◽  
Chengxu Zhou ◽  
Nikos Tsagarakis ◽  
Darwin Caldwell
Keyword(s):  
Center Of Mass ◽  
Humanoid Robots ◽  
Gait Pattern ◽  
Gait Patterns ◽  
Foot Placement ◽  
Inverted Pendulum Model ◽  
Gait Parameters ◽  
Pendulum Model ◽  
Single Mass ◽  
Walking Velocity

This paper presents a novel online walking control that replans the gait pattern based on our proposed foot placement control using the actual center of mass (COM) state feedback. The analytic solution of foot placement is formulated based on the linear inverted pendulum model (LIPM) to recover the walking velocity and to reject external disturbances. The foot placement control predicts where and when to place the foothold in order to modulate the gait given the desired gait parameters. The zero moment point (ZMP) references and foot trajectories are replanned online according to the updated foothold prediction. Hence, only desired gait parameters are required instead of predefined or fixed gait patterns. Given the new ZMP references, the extended prediction self-adaptive control (EPSAC) approach to model predictive control (MPC) is used to minimize the ZMP response errors considering the acceleration constraints. Furthermore, to ensure smooth gait transitions, the conditions for the gait initiation and termination are also presented. The effectiveness of the presented gait control is validated by extensive disturbance rejection studies ranging from single mass simulation to a full body humanoid robot COMAN in a physics based simulator. The versatility is demonstrated by the control of reactive gaits as well as reactive stepping from standing posture. We present the data of the applied disturbances, the prediction of sagittal/lateral foot placements, the replanning of the foot/ZMP trajectories, and the COM responses.

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