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Analyse biomécanique du mouvement de préhension contraint et altéré : indices quantitatifs de la gestion de la redondance motrice

Abstract : Through the assessment of quantitative indexes, this work focused on the biomechanical analysis of the upper limb redundancy and motor coordination during a reach-to-grasp movement. Based on the Uncontrolled Manifold approach, we considered, on one hand, a particular aspect of the synergies, i.e. the covaration of elemental variables of a system that lead to a stabilization of a particular performance variable. In this framework, it was hypothesized that degrees of freedom were not frozen as suggested by Bernstein but combined in order to ensure performance and stability. On the other hand, we used a robotic index, the manipulability, allowing the assessment of wrist displacement capacities during the grasping task. The aim of the present work was to study the motor coordination during constrained and altered upper limb movements through the evaluation of these two. In this framework, the first analysis consisted in evaluating the effect of a spatial constraint materialized by an obstacle during the transport phase of the reach-to-grasp movement. The second part consisted in identifying motor coordination of the upper limb for spinal cord injury patients, especially quadriplegic patients, using both kinematics and electromyographic (EGM) analyses. Two experiments were conducted to record kinematics and EMG activity of upper limb muscles with adapted apparatus. In the presence of an obstacle, results showed that wrist Cartesian trajectory was stabilized through flexible combination of joint synergy. Also, the results showed an increase of goal equivalent configurations to stabilize the elbow trajectory when an obstacle was present. This result suggests that the increase of the joint angle flexibility may be a mechanism by which the central nervous system takes into account a spatial constraint during obstacle avoidance. In the same time, the increase of the manipulability of the wrist joint center was found. For quadriplegic patients, EMG analysis showed a compensation of the weakness or paralysis of particular muscles, particularly the triceps brachii, by an increase of the relative activation of the shoulder muscles. In addition, these subjects presented a variance decomposition similar to the one of the control group suggesting that, despite the presence of a motor deficiency, goal equivalent joint configuration during the execution of the movement are still present or have been recovered. Also, for manipulability, patients have strong similarities with the control group. Considering these results, we think that the exploration of synergies through the proposed indices could be an interesting tool to study the impact of external constraint and impairment on the biomechanical parameters of movement. These works open the way for interesting applications in the field of movement simulation by considering the variability of joint trajectories in relation to a performance variable. Also, they may be applied to the assessment of the coordination of impaired subjects in order to evaluate and improve rehabilitation programs by providing quantitative information on the contribution of all the degrees of freedom.
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Julien Jacquier-Bret. Analyse biomécanique du mouvement de préhension contraint et altéré : indices quantitatifs de la gestion de la redondance motrice. Autre [q-bio.OT]. Université du Sud Toulon Var, 2009. Français. ⟨tel-00530468⟩

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