Context of the visit: The proposed visit will be one of the first pieces of a wider project of the Luxembourg Research Group that aims to build a gait simulator reproducing the impact of pathological impairments and other alterations on gait pattern. This project is based on several ongoing national and international collaborations and co-supervisions of MSc students and post-doctoral fellows.Aim of the project: Many neuro-orthopaedics pathologies involve impairments that compromise normal movement. Clinically, preservation of gait with the minimum of abnormalities is the goal of many treatments. In order to optimise these treatments, understanding mechanisms of kinematic abnormalities and identifying the impairments leading to them is of primary importance. However, despite the relationship between abnormalities and impairments makes no doubt, the individual contributions of each impairment to these abnormalities is not trivial and rarely elucidated. The simulator will bring a deeper understanding about the origin of the kinematic abnormalities observed during gait in pathologic populations. One core assumption is that by isolating impairments, the simulator will facilitate the understanding of individual impairment contributions to these abnormalities. Furthermore, by combining impairments, it will be possible to replicate pathological conditions and compare predicted and pathological kinematic abnormalities. This is an essential step towards personalised rehabilitation.Literature review: Different approaches have already been proposed in the literature to understand the relationship between impairments and kinematic abnormalities. In particular, computer simulations offer an interesting framework avoiding ethical issues and bringing the potential to manage what-if scenarios. Even if the validation of the related models remains an issue, this approach is already a powerful understanding and educative tool to study complex phenomena. Several simulation studies have already been conducted towards the introduction of impairments in the models. However, only few studies used this approach to observe the impact of impairments on kinematic abnormalities. Indeed, most of studies investigated to which extend an alteration can be tolerated without altering the original kinematics. Consequently, the impact of impairments on kinematic abnormalities remains poorly investigated.Objective of the visit: The proposed visit aims to develop a new simulation framework in which individual or combined impairments can be introduced to alter a musculoskeletal model. This framework will be used in the future as a core method of the intended gait simulator. In order to enable predictive simulations, our framework will be based on a forward dynamic approach adapted to our previously developed musculoskeletal model. For that, an optimal control problem will be defined to solve the muscular redundancy problem using a direct multiple shooting method recently adapted to musculoskeletal modelling by the S2M laboratory. This approach will allow the investigation of the effects on gait pattern of any alteration on the original model, to enable the prediction of kinematic consequences and abnormalities. As suggested in the literature, muscle weakness will be simulated by altering the activation’s upper bound of the targeted muscles to simulate paresis, and by altering the maximal isometric muscle force to simulate atrophy. Muscle spasticity will be simulated by defining a muscular activation that is velocity-dependent over a predefined threshold. Finally, soft tissue contracture will be simulated by altering the passive force-length curve, described in a Hill-type muscle model.Expected outcomes: The simulation framework will offer a new tool to the scientific community for gait simulation. In the long term, the related project will provide a valuable clinical and educational framework to simulate and understand altered gait patterns.