La réalisation d’une action motrice implique l’activation simultanée des muscles agonistes et antagonistes contrôlés par le système nerveux central. Un traumatisme médullaire détériore la moelle épinière, entrainant une déficience motrice et des modifications du contrôle des activations musculaires. Ce travail étudie la réorganisation des activations musculaires, des activations corticales et des interactions corticomusculaires (ICM) d’un groupe traumatisé médullaire cervical (SCI) et d’un groupe contrôle (AB) lors de flexions et d'extensions isométriques autour de l’articulation du coude. En extension, nos résultats ont mis en évidence une altération des capacités de force maximale chez les SCI, associée à une augmentation des activations musculaires, une activation corticale identique aux AB et une diminution de l’implication du M1 dans le contrôle des activations musculaires. En flexion, la force développée, les activations corticales et les ICM étaient similaires chez les SCI et AB, mais les activations antagonistes et la difficulté à inhiber la contraction étaient plus importantes chez les SCI. Pour l’ensemble des participants, les ICM en flexion étaient différentes selon la fonction des groupes musculaires. Ces résultats suggèrent une altération du contrôle cortical des mécanismes inhibiteurs spinaux de la contraction musculaire après un traumatisme médullaire mais indiquent que le cortex moteur reste fonctionnel pour contrôler un acte moteur malgré l’atrophie des muscles extenseurs. Ces résultats pourraient trouver des applications cliniques pour l’élaboration de neuroprothèses nécessitant un contrôle simultané de différents groupes musculaires. / The realization of a motor action involves simultaneous activation of both agonist and antagonist muscles controlled by the central nervous system. Following spinal cord injury, damage to the spinal cord causes both a loss of motor efficiency and changes in the control of muscle activations. In the present work, we studied the reorganization of muscle activations, cortical activations and corticomuscular interactions (ICM) in spinal cord injured (SCI) and able-bodied (AB) participants during voluntary isometric contractions in flexion and extension around the elbow joint. In extension, our results showed altered capacity of maximum force production in SCI participants, associated with increased muscle activations, similar cortical activation and decreased involvement of M1 in the control of muscle activations when compared to AB participants. In flexion, the force capacities, cortical activations and ICM were similar between SCI and AB participants, but the activation of antagonistic muscles and the difficulty to inhibit the contraction were greater in SCI participants. For all participants in flexion, ICM were different depending on the function of the muscle groups. Taken together, these results suggest an alteration of the cortical control of spinal inhibitory mechanisms following a spinal cord injury, but suggest that the motor cortex remain functional to control a motor act despite the atrophy of the extensor muscles. These results could find clinical applications for the development of neuroprotheses involving simultaneous control of different muscle groups.

Title: Effect of cold water immersion on intermittent isometric forearm flexor contractions to failure in rock climbers Objectives: The aim of this study was to determine the effect of cold water immersion on intermittent isometric forearm flexor contraction to failure in rock climbers. Methods: Thirty-two climbers (15 male and 17 female) completed three intermittent trials to failure, on a climbing-specific handgrip dynamometer, on three separate visits to the laboratory. For each visit a different recovery strategy was employed: passive recovery (PAS), cold water immersion at 8 řC (CWI 8) or 15 řC (CWI 15). The force time integral (FTI - time of contraction multiplied by the force of contraction) was determined to assess intermittent performance. The tissue saturation index (TSI) and total haemoglobin (tHb) during isometric contractions from near-infrared spectroscopy (NIRS) were determined to assess hemodynamic changes. Differences between repeated trials and three recovery protocols, derived parameters NIRS, were assessed using repeated measures ANOVA with Bonferroni corrections. Results: There was no significant difference between conditions after trial one. In response to the PAS recovery condition there was a 10% and 22% decrease in FTI in the second and third trials, respectively. The PAS...

Title: Effect of cold water immersion on intermittent isometric forearm flexor contractions to failure in rock climbers Objectives: The aim of this study was to determine the effect of cold water immersion on intermittent isometric forearm flexor contraction to failure in rock climbers. Methods: Thirty-two climbers (15 male and 17 female) completed three intermittent trials to failure, on a climbing-specific handgrip dynamometer, on three separate visits to the laboratory. For each visit a different recovery strategy was employed: passive recovery (PAS), cold water immersion at 8 řC (CWI 8) or 15 řC (CWI 15). The force time integral (FTI - time of contraction multiplied by the force of contraction) was determined to assess intermittent performance. The tissue saturation index (TSI) and total haemoglobin (tHb) during isometric contractions from near-infrared spectroscopy (NIRS) were determined to assess hemodynamic changes. Differences between repeated trials and three recovery protocols, derived parameters NIRS, were assessed using repeated measures ANOVA with Bonferroni corrections. Results: There was no significant difference between conditions after trial one. In response to the PAS recovery condition there was a 10% and 22% decrease in FTI in the second and third trials, respectively. The PAS...