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Research Papers

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

[+] Author and Article Information
Evandro Ficanha

Mem. ASME
Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
Houghton, MI 49931
e-mail: emficanh@mtu.edu

Guilherme Ribeiro

Mem. ASME
Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
Houghton, MI 49931
e-mail: garamizo@mtu.edu

Lauren Knop

Mem. ASME
Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
Houghton, MI 49931
e-mail: lknop@mtu.edu t

Mo Rastgaar

Mem. ASME
Department of Mechanical
Engineering-Engineering Mechanics,
Michigan Technological University,
Houghton, MI 49931
e-mail: rastgaar@mtu.edu

Manuscript received September 20, 2017; final manuscript received November 21, 2017; published online January 30, 2018. Editor: William Durfee.

J. Med. Devices 12(1), 011010 (Jan 30, 2018) (5 pages) Paper No: MED-17-1312; doi: 10.1115/1.4039011 History: Received September 20, 2017; Revised November 21, 2017

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.

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References

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Figures

Grahic Jump Location
Fig. 3

Contour plots of the normalized damping from 7% to 93% SL. Solid line: Damping. Dashed lines: ± Standard deviation.

Grahic Jump Location
Fig. 2

Contour plots of the normalized stiffness from 7% to 93% SL. Solid line: Stiffness. Dashed lines: ± Standard deviation.

Grahic Jump Location
Fig. 1

Vibrating platform and its main components

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