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Research Papers

Development of a Subject-Specific Foot-Ground Contact Model for Walking

[+] Author and Article Information
Jennifer N. Jackson

Department of Biomedical Engineering,
University of Florida,
Gainesville, FL 32611;
Functional and Applied Biomechanics Section,
Rehabilitation Medicine Department,
National Institutes of Health,
Bethesda, MD 20892

Chris J. Hass

Department of Applied Physiology
and Kinesiology,
University of Florida,
Gainesville, FL 32611

Benjamin J. Fregly

Department of Mechanical
and Aerospace Engineering;
Department of Biomedical Engineering,
University of Florida,
Gainesville, FL 32611-6250
e-mail: fregly@ufl.edu

1Corresponding author.

Manuscript received September 14, 2015; final manuscript received June 11, 2016; published online July 28, 2016. Assoc. Editor: Kenneth Fischer.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J Biomech Eng 138(9), 091002 (Jul 28, 2016) (12 pages) Paper No: BIO-15-1454; doi: 10.1115/1.4034060 History: Received September 14, 2015; Revised June 11, 2016

Computational walking simulations could facilitate the development of improved treatments for clinical conditions affecting walking ability. Since an effective treatment is likely to change a patient's foot-ground contact pattern and timing, such simulations should ideally utilize deformable foot-ground contact models tailored to the patient's foot anatomy and footwear. However, no study has reported a deformable modeling approach that can reproduce all six ground reaction quantities (expressed as three reaction force components, two center of pressure (CoP) coordinates, and a free reaction moment) for an individual subject during walking. This study proposes such an approach for use in predictive optimizations of walking. To minimize complexity, we modeled each foot as two rigid segments—a hindfoot (HF) segment and a forefoot (FF) segment—connected by a pin joint representing the toes flexion–extension axis. Ground reaction forces (GRFs) and moments acting on each segment were generated by a grid of linear springs with nonlinear damping and Coulomb friction spread across the bottom of each segment. The stiffness and damping of each spring and common friction parameter values for all springs were calibrated for both feet simultaneously via a novel three-stage optimization process that used motion capture and ground reaction data collected from a single walking trial. The sequential three-stage process involved matching (1) the vertical force component, (2) all three force components, and finally (3) all six ground reaction quantities. The calibrated model was tested using four additional walking trials excluded from calibration. With only small changes in input kinematics, the calibrated model reproduced all six ground reaction quantities closely (root mean square (RMS) errors less than 13 N for all three forces, 25 mm for anterior–posterior (AP) CoP, 8 mm for medial–lateral (ML) CoP, and 2 N·m for the free moment) for both feet in all walking trials. The largest errors in AP CoP occurred at the beginning and end of stance phase when the vertical ground reaction force (vGRF) was small. Subject-specific deformable foot-ground contact models created using this approach should enable changes in foot-ground contact pattern to be predicted accurately by gait optimization studies, which may lead to improvements in personalized rehabilitation medicine.

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Figures

Grahic Jump Location
Fig. 1

Viscoelastic element placement for the right foot. The heel, toe, and medial and lateral toe markers were used to define a uniform rectangular grid (5 × 11 elements), where x's denote viscoelastic elements and circles denote surface markers. The elements are separated into active HF, active FF, and inactive elements. The black line is the shoe outline and the gray line is the toes axis.

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Fig. 2

Comparison of model (red-lighter) and experimental (blue-darker) ground reaction quantities for the right (solid) and left (dashed) foot. The top row shows AP, superior–inferior (normal), and ML force comparisons, respectively, and the bottom row shows CoP location in the AP and ML directions and free moment comparisons, respectively.

Grahic Jump Location
Fig. 3

Comparison of model (red-lighter solid) and experimental (blue-darker solid) joint position curves for the right foot over one gait cycle excluded from calibration. The top row shows HF translations, the middle row shows HF rotations (3-1-2 rotation sequence), and the bottom row shows toe flexion.

Grahic Jump Location
Fig. 4

Comparison of model (red-lighter dashed) and experimental (blue-darker dashed) kinematic curves for the left foot over one gait cycle excluded from calibration. The top row shows HF translations, the middle row shows HF rotations (3-1-2 rotation sequence), and the bottom row shows toe flexion.

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