Vertical Center Of Mass Trajectory Research Articles

Mind your step: Target walking task reveals gait disturbance in individuals with incomplete spinal cord injury

BackgroundWalking over obstacles requires precise foot placement while maintaining balance control of the center of mass (CoM) and the flexibility to adapt the gait patterns. Most individuals with incomplete spinal cord injury (iSCI) are capable of overground walking on level ground; however, gait stability and adaptation may be compromised. CoM control was investigated during a challenging target walking (TW) task in individuals with iSCI compared to healthy controls. The hypothesis was that individuals with iSCI, when challenged with TW, show a lack of gait pattern adaptability which is reflected by an impaired adaptation of CoM movement compared to healthy controls.MethodsA single-center controlled diagnostic clinical trial with thirteen participants with iSCI (0.3–24 years post injury; one subacute and twelve chronic) and twelve healthy controls was conducted where foot and pelvis kinematics were acquired during two conditions: normal treadmill walking (NW) and visually guided target walking (TW) with handrail support, during which participants stepped onto projected virtual targets synchronized with the moving treadmill surface. Approximated CoM was calculated from pelvis markers and used to calculate CoM trajectory length and mean CoM Euclidean distance TW-NW (primary outcome). Nonparametric statistics, including spearman rank correlations, were performed to evaluate the relationship between clinical parameter, outdoor mobility score, performance, and CoM parameters (secondary outcome).ResultsHealthy controls adapted to TW by decreasing anterior–posterior and vertical CoM trajectory length (p < 0.001), whereas participants with iSCI reduced CoM trajectory length only in the vertical direction (p = 0.002). Mean CoM Euclidean distance TW-NW correlated with participants’ neurological level of injury (R = 0.76, p = 0.002) and CoM trajectory length (during TW) correlated with outdoor mobility score (R = − 0.64, p = 0.026).ConclusionsThis study demonstrated that reduction of CoM movement is a common strategy to cope with TW challenge in controls, but it is impaired in individuals with iSCI. In the iSCI group, the ability to cope with gait challenges worsened the more rostral the level of injury. Thus, the TW task could be used as a gait challenge paradigm in ambulatory iSCI individuals.Trial registration Registry number/ ClinicalTrials.gov Identifier: NCT03343132, date of registration 2017/11/17.

Knee-stretched walking with toe-off and heel-strike for a position-controlled humanoid robot based on model predictive control

Knee-stretched walking is considered to be a human-like and energy-efficient gait. The strategy of extending legs to obtain vertical center of mass trajectory is commonly used to avoid the problem of singularities in knee-stretched gait generation. However, knee-stretched gait generation utilizing this strategy with toe-off and heel-strike has kinematics conflicts at transition moments between single support and double support phases. In this article, a knee-stretched walking generation with toe-off and heel-strike for the position-controlled humanoid robot has been proposed. The position constraints of center of mass have been considered in the gait generation to avoid the kinematics conflicts based on model predictive control. The method has been verified in simulation and validated in experiment.

Biomechanically Excited SMD Model of a Walking Pedestrian

AbstractThrough their biomechanical properties, pedestrians interact with the structures they occupy. Although this interaction has been recognized by researchers, pedestrians’ biomechanical properties have not been fully addressed. In this paper, a spring-mass-damper (SMD) system, with a pair of biomechanical forces, was used to model a pedestrian for application in vertical human–structure interaction (HSI). Tests were undertaken in a gait laboratory, where a three-dimensional motion-capture system was used to record a pedestrian’s walking motions at various frequencies. The motion-capture system produced the pedestrian’s center of mass (COM) trajectories from the captured motion markers. The vertical COM trajectory was approximated to be the pedestrian SMD dynamic responses under the excitation of biomechanical forces. SMD model parameters of a pedestrian for a specific walking frequency were estimated from a known walking frequency and the pedestrian’s weight, assuming that pedestrians always walk in ...

Stable Walking of Humanoid Robots Using Vertical Center of Mass and Foot Motions by an Evolutionary Optimized Central Pattern Generator

This paper proposes a method to produce the stable walking of humanoid robots by incorporating the vertical center of mass (COM) and foot motions, which are generated by the evolutionary optimized central pattern generator (CPG), into the modifiable walking pattern generator (MWPG). The MWPG extends the conventional 3-D linear inverted pendulum model (3-D LIPM) by allowing a zero moment point (ZMP) variation. The disturbance caused by the vertical COM motion is compensated in real time by the sensory feedback in the CPG. In this paper, the vertical foot trajectory of the swinging leg, as well as the vertical COM trajectory of the 3-D LIPM, are generated by the CPG for the effective compensation of the disturbance. Consequently, using the proposed method, the humanoid robot is able to walk with a vertical COM and the foot motions generated by the CPG, while modifying its walking patterns by using the MWPG in real time. The CPG with the sensory feedback is optimized to obtain the desired output signals. The optimization of the CPG is formulated as a constrained optimization problem with equality constraints and is solved by two-phase evolutionary programming (TPEP). The validity of the proposed method is verified through walking experiments for the small-sized humanoid robot, HanSaRam-IX (HSR-IX).

Stable Bipedal Walking With a Vertical Center-of-Mass Motion by an Evolutionary Optimized Central Pattern Generator

This paper proposes a method for stable bipedal walking with a vertical center-of-mass (COM) motion by an evolutionary optimized central pattern generator (CPG). To generate a walking pattern for a bipedal robot, a modifiable walking pattern generator (MWPG) is employed, which extends a conventional 3-D linear inverted pendulum model (3-D LIPM) to allow a zero-moment-point variation by the closed-form functions. By using the MWPG, the robot is able to modify the walking pattern in real time while walking. For the vertical COM motion of the 3-D LIPM, the vertical COM trajectory is generated by the CPG. The disturbance caused by the vertical COM motion is compensated by utilizing the sensory feedback in the CPG. To obtain the desired output signals from the CPG, the CPG is optimized by the two-phase evolutionary programming (TPEP), which is suitable to solve the constrained optimization problems. By combining the MWPG with the CPG, stable bipedal walking with a larger stride is obtained. The validity of the proposed method is verified through real experiments for the small-sized bipedal robot, HanSaRam-IX.

Validation of a protocol for the estimation of three-dimensional body center of mass kinematics in sport

Since strictly related to balance and stability control, body center of mass (CoM) kinematics is a relevant quantity in sport surveys. Many methods have been proposed to estimate CoM displacement. Among them, segmental method appears to be suitable to investigate CoM kinematics in sport: human body is assumed as a system of rigid bodies, hence the whole-body CoM is calculated as the weighted average of the CoM of each segment. The number of landmarks represents a crucial choice in the protocol design process: one have to find the proper compromise between accuracy and invasivity. In this study, using a motion analysis system, a protocol based upon the segmental method is validated, adopting an anatomical model comprising 14 landmarks. Two sets of experiments were conducted. Firstly, our protocol was compared to the ground reaction force method (GRF), accounted as a standard in CoM estimation. In the second experiment, we investigated the aerial phase typical of many disciplines, comparing our protocol with: (1) an absolute reference, the parabolic regression of the vertical CoM trajectory during the time of flight; (2) two common approaches to estimate CoM kinematics in gait, known as sacrum and reconstructed pelvis methods. Recognized accuracy indexes proved that the results obtained were comparable to the GRF; what is more, during the aerial phases our protocol showed to be significantly more accurate than the two other methods. The protocol assessed can therefore be adopted as a reliable tool for CoM kinematics estimation in further sport researches.

3-D Command State-Based Modifiable Bipedal Walking on Uneven Terrain

Bipedal robots in previous research work were unable to independently modify the elements of a walking pattern on uneven terrain without any extra footstep for adjusting the center of mass (COM) motion. To solve this problem, this paper extends the modifiable walking pattern generator (MWPG). The MWPG can independently modify the elements of the walking pattern without any extra footstep on flat terrain only. The extended MWPG can be applied on uneven terrain. In the extended MWPG, a 3-D command state is defined to generate the walking pattern on uneven terrain. Instead of using the constant COM height, the vertical COM trajectory is generated to satisfy the foot height of the swing leg. Also, an additional trajectory, generated by the cubic spline interpolation, is supplied to the vertical foot trajectory of the MWPG. The proposed MWPG is implemented on the small-sized bipedal robot, HanSaRam-IX (HSR-IX) and the effectiveness of the proposed MWPG is demonstrated through the experiment.

Contribution of the six major gait determinants on the vertical center of mass trajectory and the vertical ground reaction force

Saunders et al. (1953) stated that the introduction of six gait determinants (pelvic rotation, pelvic obliquity, stance knee flexion, foot and ankle mechanisms, and tibiofemoral angle) to a compass gait model (two rigid legs hinged at the hips) provides an accurate simulation of the actual trajectory of the whole body center of mass (CoM). Their respective actions could also explain the shape of the vertical ground reaction force (GRF) pattern. Saunders’ approach is considered as a kinematic description of some features of gait and is subject to debate. The purpose of this study is to realize a rigorous mechanical evaluation of the gait determinants theory using an appropriated mathematical model in which specific experimental data of gait trials are introduced. We first simulate a compass-like CoM trajectory using the proposed 3D mathematical model. Then, factorizing the model to introduce successively the kinematic data related to each gait determinant, we assess their respective contribution to both the CoM trajectory and the pattern of vertical GRF at different gait speeds. The results show that the stance knee flexion significatively decreases the estimated position of the CoM during midstance. Stance knee extension and pelvic obliquity contribute to the appearance of the pattern of vertical GRF during stance. The stance ankle dorsiflexion significatively contributes to CoM vertical excursion and the ankle plantarflexion contributes to the vertical GRF during terminal stance. The largest contribution towards the minimization of the CoM vertical amplitude during the complete gait step appears when considering the foot mechanisms and the pelvic obliquity in the proposed model.

Effect of Ankle-Foot Orthoses on the Sagittal Plane Displacement of the Center of Mass in Patients With Stroke Hemiplegia: A Pilot Study

Background: Ankle-foot orthoses (AFOs) have been reported to have positive effects on the temporal-spatial parameters and kinematics and kinetics of gait in patients with stroke. The center of mass (COM) may be used to represent whole body movement and energy cost in gait, and therefore COM movement would also be positively influenced with use of an appropriate AFO. Objective: To investigate the effect of AFOs on the sagittal plane displacement of the COM in patients with stroke hemiplegia. Methods: Five male subjects with stroke hemiplegia participated in this pilot study. The trajectory of the COM in the sagittal plane, gait speed, bilateral step length, step width, and bilateral stance time were analyzed while participants ambulated under 2 test conditions: with an AFO or with footwear only. The height of the 2 peaks of the vertical displacement of the COM in a gait cycle was subsequently measured and normalized to body height. Statistical analyses were conducted using a nonparametric Friedman test. Results: Gait speed, bilateral step length, and the normalized peak height of the vertical COM trajectory during stance phase on the affected leg all revealed statistically significant increases (P < .05), and step width showed significant decreases (P < .05) under the AFO condition when compared to the footwear-only condition. Conclusions: An AFO may influence the vertical displacement of the COM in patients with stroke hemiplegia. The results of this pilot study therefore suggested that vertical movement of COM could potentially serve as a useful parameter to evaluate the effect of an AFO.

Adapting Locomotion to Different Surface Compliances: Neuromuscular Responses and Changes in Movement Dynamics

Knowledge of how the nervous system deals with surfaces with different physical properties such as compliance that challenge balance during locomotion is of importance as we are constantly faced with these situations every day. The purpose of this study was to examine the control of center of mass (COM) and lower limb dynamics and recovery response modulation of muscle activity during locomotion across an unexpected compliant surface and in particular, scaling behavior across different levels of compliance. Eight young adults walked along a walkway and stepped on an unexpected compliant surface in the middle of the travel path. There were three different levels of surface compliance, and participants experienced either no compliant surface or one of the three compliant surfaces during each trial that were presented in a blocked or random fashion. Whole body kinematics were collected along with surface electromyography (EMG) of selected bilateral lower limb and trunk muscles. The recovery response to the first compliant-surface trial demonstrated muscle onset latencies between 97 and 175 ms, and activity was modulated while on the compliant surface. Vertical COM trajectory was not preserved after contact with the compliant surface: peak vertical COM, while on the compliant surface was lower than when on stable ground. Perturbed-limb knee flexion after toe-off increased with increased surface compliance, which enabled toe clearance with the ground to be similar to control trials. The results suggest that stepping off of a compliant surface is actively modulated by the CNS and is geared toward maintaining dynamic stability.