Session: 07-05-01: Dynamics and Control of Biomechanical Systems

Paper Number: 167617

Dynamic Shear Deformation and Postural Adaptation Under Perturbations 

This paper examines the dynamic biomechanical behavior of the human foot by investigating shear deformation and postural adaptation under externally perturbed conditions. In contrast to static models, the dynamic analysis focuses on the alterations in kinematic and kinetic responses when the foot is exposed to controlled disturbances. Fourteen healthy subjects were recruited for experiments that incorporated both quiet stance and perturbed standing trials. Sensors were strategically placed on the navicular, metatarsal, and calcaneus regions to capture three-dimensional motion data, while a force plate provided complementary kinetic measurements.

The investigation is built upon three interrelated hypotheses addressing the dynamic response of the foot. The fourth hypothesis examines whether the foot undergoes shear deformation during stance. This is evaluated through quaternion-derived rotation axes; if the analysis reveals a consistent axis that exhibits primarily translational movement with negligible rotational changes, then the presence of shear deformation is confirmed. The fifth hypothesis explores postural kinematics during perturbed standing by assessing the relationship between the center of pressure (COPx) obtained from the force plate and the center of mass (COMx) derived from the sensor data. It is hypothesized that an anterior shift in the COM, accompanied by corresponding variations in friction force along the X-axis, will reflect a sliding mode of action that is indicative of shear deformation.

The sixth hypothesis posits that the rigidity of the foot diminishes under perturbation. This is assessed by comparing the inter-segment distances—specifically, the calcaneus-metatarsal gap—and the angular relationships among the calcaneus, navicular, and metatarsal during quiet versus perturbed conditions. An increase in these metrics during dynamic trials would signify that the foot loses its inherent rigidity when challenged by external forces .

Subjects were subjected to controlled perturbations while standing on a calibrated force plate, ensuring that the dynamic response was recorded with high fidelity. Data analysis involved advanced statistical techniques to compare static and perturbed conditions. The results reveal significant alterations in postural kinematics under dynamic loading, with marked changes in both the COPx and COMx positions. These changes, together with variations in friction force, support the presence of a sliding mode that correlates with shear deformation. Moreover, the increased inter-segmental distances and angular deviations under perturbation provide clear evidence of a loss of foot rigidity.

The findings of this study have broad implications. By demonstrating that the foot’s biomechanical behavior shifts markedly under dynamic conditions, the research challenges traditional static models and supports the integration of dynamic factors into biomechanical analyses. The insights gained here are particularly relevant for the design of responsive orthotic devices and rehabilitation protocols that must accommodate the complex interplay between shear forces and postural stability. In conclusion, this study establishes a comprehensive framework for understanding the dynamic behavior of the foot, highlighting the critical role of shear deformation and the loss of rigidity in postural adaptation.

Keywords: shear deformation, dynamic foot biomechanics, perturbed stance, postural adaptation, kinematic analysis, force plate measurements.

Presenting Author: Senih Gürses Middle East Technical University

Presenting Author Biography: Asst. Prof. Senih Gürses is a faculty member at the Department of Engineering Sciences at Middle East Technical University (METU), Ankara, Turkey. His research focuses on biomechanics, human postural control, somatosensory and vestibular interactions, and the mechanical analysis of foot-ground dynamics during stance and movement. He has supervised numerous postgraduate and doctoral theses in these fields, contributing significantly to the understanding of sensory integration in human balance.

Dr. Gürses has published extensively in high-impact journals indexed in SCI, SSCI, and AHCI, including Experimental Brain Research, Journal of Biomechanical Engineering, Materials Today Communications, and Biomedicine and Pharmacotherapy. His interdisciplinary work bridges engineering, neuroscience, and clinical biomechanics.

He is actively involved in international collaborations and has contributed to research on motor performance, neurostimulation, exoskeleton dynamics, and biomaterials for orthopedic applications. Dr. Gürses also serves as a mentor for early-stage researchers and continues to advance experimental and computational modeling techniques in biomechanics.

Authors:

Esra Gözde Yalçın Yıldırım ROKETSAN
Kutluk Bilge Arıkan Ankara University
Senih Gürses Middle East Technical University