Time-varying human ankle impedance in the sagittal and frontal planes during stance phase of walking

Ficanha, Evandro M.; Ribeiro, Guilherme Aramizo; Knop, Lauren; Rastgaar, Mo

doi:10.1109/icra.2017.7989786

Cited by 10 publications

(10 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To estimate the impedance, the vibrating platform was used as described in previous work [1]. The right shank, right foot, and vibrating platform were instrumented with optical markers for motion capturing.…”

Section: Methodsmentioning

confidence: 99%

“…The impedance modulation of the human ankle is required for stable walking. The estimation of the time-varying impedance modulation of the human ankle is the focus of research by different groups [1,2].The human body can be modeled as an inverted pendulum with a rocker shaped based [3]. In this model, the body is unstable if the radius of the rocker base is smaller than the height of the center of the mass.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Impedance of the Human Ankle During Standing for Posture Control

Ribeiro

Ficanha

Knop

et al. 2018

2018 Design of Medical Devices Conference

View full text Add to dashboard Cite

BACKGROUNDThe stiffness and damping of anatomical joints can be modulated by muscle co-contraction, where antagonistic muscles contract simultaneously, increasing both the joint's stiffness and damping. In a second order system, the mechanical impedance, or simply impedance, is a function of the system's inertia, damping, and stiffness. The ankle impedance can be defined as the resultant force due to an external motion perturbation. The impedance modulation of the human ankle is required for stable walking. The estimation of the time-varying impedance modulation of the human ankle is the focus of research by different groups [1,2].The human body can be modeled as an inverted pendulum with a rocker shaped based [3]. In this model, the body is unstable if the radius of the rocker base is smaller than the height of the center of the mass. This means that the body is unstable during walking and standing, unless external forces are applied [4]. The ankle quasi-stiffness and the rocker radius are directly related, meaning a larger quasi-stiffness will result in a larger rocker radius. The quasi-stiffness of a joint is defined as the slope of the torque angle curve of a joint during an activity, and it is not necessarily the same as the stiffness. It has been shown that for stability, the rocker shape radius and quasi-stiffness in the sagittal plane are larger during stance than during walking. The required quasi-stiffness are 458 N.m/rad for stable walking and 1432 N.m/rad for standing in a 71 kg person and a leg length of 1 m [4].A previous study has shown that, different from stable walking, ankle stiffness on the sagittal plane during quiet standing is not neurally controlled to maintain postural stability [5]. Instead, the main mechanism for balancing is the modulation of the ankle torque by the neural system, with a very small stiffness variation. This paper studies the ankle properties during standing, analyzing whether the stiffness and damping

show abstract

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Impedance of the Human Ankle During Standing for Posture Control

Ribeiro

Ficanha

Knop

et al. 2018

2018 Design of Medical Devices Conference

View full text Add to dashboard Cite

show abstract

“…For simplicity, mechanical impedance may be simply referred to as impedance in this paper. The ankle impedance at low frequencies has little effect of damping and inertia and is closely representative of the ankle's stiffness [3,4]. The ankle impedance in dorsiflexion-plantarflexion (DP) at low frequencies has been one of the primary parameters in the design of active ankle-foot prostheses and lower extremity rehabilitation devices.…”

Section: Introductionmentioning

confidence: 99%

Estimation of the Two Degrees-of-Freedom Time-Varying Impedance of the Human Ankle

Evandro

Guiherme

Knop

et al. 2018

Journal of Medical Devices

Self Cite

View full text Add to dashboard Cite

An understanding of the time-varying mechanical impedance of the ankle during walking is fundamental in the design of active ankle-foot prostheses and lower extremity rehabilitation devices. This paper describes the estimation of the time-varying mechanical impedance of the human ankle in both dorsiflexion–plantarflexion (DP) and inversion–eversion (IE) during walking in a straight line. The impedance was estimated using a two degrees-of-freedom (DOF) vibrating platform and instrumented walkway. The perturbations were applied at eight different axes of rotation combining different amounts of DP and IE rotations of four male subjects. The observed stiffness and damping were low at heel strike, increased during the mid-stance, and decreases at push-off. At heel strike, it was observed that both the damping and stiffness were larger in IE than in DP. The maximum average ankle stiffness was 5.43 N·m/rad/kg at 31% of the stance length (SL) when combining plantarflexion and inversion and the minimum average was 1.14 N·m/rad/kg at 7% of the SL when combining dorsiflexion and eversion. The maximum average ankle damping was 0.080 Nms/rad/kg at 38% of the SL when combining plantarflexion and inversion, and the minimum average was 0.016 Nms/rad/kg at 7% of the SL when combining plantarflexion and eversion. From 23% to 93% of the SL, the largest ankle stiffness and damping occurred during the combination of plantarflexion and inversion or dorsiflexion and eversion. These rotations are the resulting motion of the ankle's subtalar joint, suggesting that the role of this joint and the muscles involved in the ankle rotation are significant in the impedance modulation in both DP and IE during gait.

show abstract

“…The next step of this work is to estimate the impedance of a human during walk, which was reported to have time-varying characteristics through the gait cycle [11][12][13]. Another step is to separate the intrinsic impedance from the nonlinear reflexive component.…”

Section: Inertia Estimation Using the Instrumented Vibrating Platformmentioning

confidence: 99%

“…On the execution layer, control engineers often opt for a controller with ankle compliance during the stance phase, such as emulating a stiffness [10] or an impedance [7] of a healthy walk. Additionally, the ankle has been reported to change its impedance across the cycle of the straight walk [11][12][13]. But prosthesis controllers cannot address these problems because there is no reported work quantifying the impedance as a function of ground slopes or gait maneuver.…”

Section: Introductionmentioning

confidence: 99%

Control of a Powered Ankle-Foot Prosthesis: From Perception to Impedance Modulation

Ribeiro¹

View full text Add to dashboard Cite

Time-varying human ankle impedance in the sagittal and frontal planes during stance phase of walking

Cited by 10 publications

References 15 publications

Impedance of the Human Ankle During Standing for Posture Control

Impedance of the Human Ankle During Standing for Posture Control

Estimation of the Two Degrees-of-Freedom Time-Varying Impedance of the Human Ankle

Control of a Powered Ankle-Foot Prosthesis: From Perception to Impedance Modulation

Contact Info

Product

Resources

About