Movement biomechanics and musculoskeletal modelling

Pathologies of the musculoskeletal and neurological systems are becoming a major public health problem, not least because of the ageing population and greater access to leisure activities in industrialized countries. To achieve a better understanding and treatment of these disorders, clinical, sports and ergonomic studies are increasingly turning to the biomechanics of movement, which involves applying the tools, methods and formalisms of mechanics to the study of human movement, considering it as a system made up of rigid segments articulated together. Compared to a conventional mechanical system, however, the human body is characterized by a high degree of kinematic and muscular redundancy, as well as by a highly complex control system, which together allow for great diversity and adaptability in gestures and postures. Musculoskeletal modeling therefore seeks to provide a more detailed understanding of the contribution of different structures (joint geometry, muscles, tendons, ligaments, etc.) to a given movement.

Against this backdrop, this article aims to give the reader an overview of the various steps involved, from motion measurement to the determination of clinically interpretable results. The various devices used to measure human movement are briefly presented. This is followed by a more detailed description of the principle behind the three-dimensional reconstruction of the most commonly used systems – optoelectronic systems with passive markers –. The methods used to calculate joint kinematics, giving access to the movements of each degree of freedom of the joints from the measurements of these systems, are then described, and the errors linked to the measurement system and also to the experimental protocol used for its implementation are detailed. Before turning to musculoskeletal modeling, the inverse dynamic calculation of the moments representing the resultant action of the various muscles crossing a joint is presented. Finally, we conclude this article by outlining the main approaches used to gain access to the forces developed in the various muscles during a movement.