Digital platform for studying mechanisms (mechanics, biomechanics, sensory, cognitive, psychological) involved in the human balance preservation and recovery – EquiSim

A mechanical representation of the human body is placed in a physical simulation environment. From the estimated state of this model, possibly obtained through a sensory integration approach, a controller with an embedded internal representation of the human body aims at selecting the most appropriate actions over a time horizon to bring the mechanical model back to the desired state. This controller does not necessarily run continuously but can be called intermittently based on alerts coming from sensorial inputs.

The numerical tool developed allows simulating the choice and execution of balance maintenance actions. Different regulation mechanisms have been considered: displacement of the point of application of the contact force, variation of the angular momentum, modification of the contact points, variation of the altitude of the center of mass. This tool has been used for different scenarios, including highly perturbed situations: postural tasks, gait initiation, perturbed walking, etc. In parallel, an experimental device has been set up to study human walking in a perturbed (in a controlled way) environment.

The simulated behaviors could not be fully evaluated on experimental data acquired in a controlled manner. The device for disturbing balance during walking developed in the project will enable this evaluation. This tool could then be used to predict the risk of falling of different populations subjected to a variety of equilibrium disturbances.

Guinamard, M., Robert, T., Chèze, L., & Chabaud, P. (2018). Balance recovery reactions following various waist-pull perturbation time profiles. In 8th World Congress of Biomechanics, 8-12 July, Dublin (IR).
Le Mouel, C., Tisserand, R., Robert, T., Brette, R., (2019). Effect of the rate of change of an external balance perturbation. In 2019 ISPGR World Congress, June 30 – Jully 4, Edinburgh, (Scotland).
Robert T., Guinamard M., Chabaud P., Chèze L., Mille M.L., (2019). Postural adjustments in anticipation of predictable perturbations allow elderly fallers to achieve a balance recovery performance equivalent to elderly non-fallers. In 2019 ISPGR World Congress, June 30 – Jully 4, Edinburgh, (Scotland).
Bentaleb, T., Pajon, A., Robert, T., Wieber, P.-B. (2020). Effect of vertical motion on balance recovery prediction for standing human through linear MPC. In: Actes des Journées Nationales de la Robotique Humanoïde 2020, 25-26 juin 2020 (en ligne, France).
Le Mouel, C., Tisserand, R., Robert, T., Brette, R., 2019. Postural adjustments in anticipation of predictable perturbations allow elderly fallers to achieve a balance recovery performance equivalent to elderly non-fallers. Gait Posture 71, 131–137.

Falls represent an actual public health challenge. Fall prevention requires knowledge and understanding of multiple processes associated to balance recovery as well as their interactions: neurologic, cognitive and psychologic processes leading to the regulation of the balance recovery actions, but also the mechanical and biomechanical aspects linked to the execution of these actions and to their impact on the equilibrium. However, to date, this comprehension remains partial despite an abundant literature.

In order to overcome the challenge imposed by the fact that these processes are manifold (multiple and related to multidisciplinary aspects), we propose to use a systemic approach to model the balance recovery in its entirety. Thus, this project aims at designing a numerical platform dedicated to the modelling of human balance maintenance and recovery; its usability will be demonstrated on several case studies.

A mechanical model of the human body is developed in a simulation environment. A group of sub-systems representing the body sensory sensors and a phase of sensory integration are used to extract an estimation of the state of the physical model. This information will be processed and combined to other elements such as physical capacities, level of risk acceptation, environment knowledge… before being transferred as inputs of a controller. Its role is to determine the actions to be made, along a given time horizon, in order to maintain or bring back the physical model in the desired state. A specificity we focused on is that these “high level” data processing will not necessarily be continuously performed but could rather be triggered by warnings generated for instance by sensory information (given variables exceeding a threshold, conflict between perceived and actual state,…). Outputs of the controller are eventually applied on the physical model.

A specific care will be taken to ensure the possibility of interpretation and identification of the tool’s parameters. An experimental part of this project is dedicated to this point. This approach will necessitate compromises on the level of complexity of the models but will allow having a stable thorough tool, easy to handle and parametrize. Thus, the developed tool will allow simulating the choice and accomplishment of protective actions to maintain or recover balance in different situations, including highly perturbed ones, and for different types of population.

As a consequence, this project is very multidisciplinary, relatively upstream in the balance research field and focused on tool development. Nonetheless, this project is built in order to deal and answer several specific research questions. The central theme will be the understanding of the rise of the risk of falls among elderly people. Apart from clinical aspects, this project will have direct applications in the transportation field, with the determination of acceptable thresholds for vehicle dynamics with respect to the balance of standing passengers. Moreover, in order to increase both impact and visibility of these researches, we will use an « Open » approach, aiming at making results and knowledge gathered in this project freely available to the scientific community (open license software, open data, dissemination through open access journals …).

This project will represent a both decisive and necessary breakthrough in the study of human balance. The developed tool will allow to clearly identify dangerous situations, to better detect people at risk of fall and to better define and target the prevention actions.