Optimisation des interactions muscle-tendon pour l'amélioration de la performance lors de tâches plurisegmentaires

It is generally known in the literature that the muscle and tendon display a dissociated behaviour during tasks. Also, muscle and tendon mechanical properties differ among individuals and among the muscle-tendon units analysed. Only a few studies have tried to determine the role of these properties in muscle fascicle behaviour during multi-articular tasks. Therefore, this work aimed to determine how the muscle and tendon mechanical properties affect muscle-tendon interactions, and enable an increase in performance. For that purpose, we conducted three experiments in which we measured with ultrasound the fascicle behaviour of the gastrocnemius medialis (GM) and/or the vastus lateralis (VL) during mono- and multi-articular tasks. First, we highlighted that a heel drop eccentric training programme, inducing a slight increase in GM’s fascicle length, paired with an increase in maximal torque and tendon stiffness, did not modify the fascicle behaviour during explosive tasks, running, or vertical jumping. Second, we found an alteration of the optimal angle at increased velocities during a knee extension task, without inducing changes in the VL optimal length. Also, we highlighted that pre- activation prior to an isokinetic contraction could induce changes in fascicle optimal length, but also a reduction in maximal torque in the case of an isometric pre-activation. Third, we demonstrated that vertical jump performance is linked to an increase in the catapult effect on the GM, but also to an alteration of the VL’s fascicle behaviour during the jump, enabling them to be at more favourable lengths to produce force. These muscle-tendon optimisations were closely linked to a change in kinematics during the task.