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This article is part of the supplement: 3rd Congress of the International Foot and Ankle Biomechanics Community

Open Access Open Badges Oral presentation

Inertial control: a novel technique for in-vitro analysis of foot function

Tassos Natsakis1*, Koen Peeters1, Fien Burg1, Greta Dereymaeker1, Jos Vander Sloten1 and Ilse Jonkers2

Author Affiliations

1 Mechanical Engineering Department, KU Leuven, Leuven, 3000, Belgium

2 Department of Kinesiology, KU Leuven, Leuven, 3000, Belgium

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Journal of Foot and Ankle Research 2012, 5(Suppl 1):O42  doi:10.1186/1757-1146-5-S1-O42

The electronic version of this article is the complete one and can be found online at:

Published:10 April 2012

© 2012 Natsakis et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


In-vitro gait simulations have great potential, allowing a systematic analysis of the foot function. However, it is important that the loading conditions are realistic i.e. physiologic ground reaction forces (GRF). In most experiments, in-vivo measured GRF can be imposed [1,2]. However in experimental designs that evaluate the effect of altered muscle forces on foot motion this is more complex; the effect of the altered muscle activity on the loading and kinematics cannot be taken into consideration. Therefore, we investigated the use of a new technique to simulate such cases with realistic loading conditions.


Our gait simulator simulates the activation of nine muscles (grouped in six groups), based on electromyography measurements. The forces are applied with pneumatic actuators and are measured by load-cells located between the tendons and the actuators. The set-up is able to simulate knee motion, using a motor for the horizontal and a platform under the foot for the vertical direction. The stance phase is simulated in 0.8 seconds.

The GRF in human gait is the sum of a static (human weight) and a dynamic part (acceleration of human mass). By applying a constant force on the platform (equal to the assumed weight of the subject), the measured GRF is the sum of the constant force and the force generated from the acceleration of the platform. This way, the kinetics are governed exclusively by the muscle activation.


Four freshly frozen cadaveric specimens were used, for five measurements each. The in-vitro measured GRF was compared to in-vivo measurements (figure 1) and followed the normal pattern with an RMS error of 22%.

thumbnailFigure 1. Comparison of the in-vivo and in-vitro measured GRF.


Using this method, physiological GRF were reconstructed for normal gait, by reconstructing the mechanism that generates GRF. It could be, therefore, used for pathologic gait simulations, since the mechanism is identical.


This work was funded by the Chair Berghmans-Dereymaeker.


  1. Sharkey NA, Hamel AJ: A dynamic cadaver model of the stance phase of gait: performance characteristics and kinetic validation.

    Clin Biomech (Bristol, Avon) 1998, 13:420-433. PubMed Abstract | Publisher Full Text OpenURL

  2. Whittaker E, Aubin P, Ledoux W: Foot bone kinematics as measured in a cadaveric robotic gait simulator.

    Gait Posture 2011, 33:645-650. PubMed Abstract | Publisher Full Text OpenURL