Résumé
The microgravity conditions to which astronauts are subjected during space flight have deleterious effects on the musculoskeletal system. Contrary to muscle and bone, the effects of microgravity on tendons and their insertions are currently poorly understood. Through a multidisciplinary approach, this doctoral work focused on the biological and mechanical adaptations which occur at the achillean enthesis, the insertion of the Achilles tendon on the calcaneus, in response to simulated microgravity conditions but also in response to a return to normal mechanical loads. Our work has shown that hypoactivity leads to a disorganization of collagen fibers and a decrease in the unmineralized fibrocartilage of the enthesis without altering its tensile resistance. Under these conditions, the ability to resist to repeated compressive loading was reduced. The return to activity induced a remodelling of the achillean enthesis, characterised by an increase in the area of the fibrocartilage, a disorganisation of the collagen fibers and a loss of the mineralization gradient. Despite a loss of the local gradient of mechanical properties, the tensile strength of the enthesis was not impaired and the compressive fatigability was restored. As the tendon-to-bone insertion is a structure sensitive to microgravity and remobilisation, the findings of our work highlight the relevance of considering the response of the enthesis in the strategies to prevent the effects of deconditioning as well as in the rehabilitation strategies of spacemen upon returning from their mission.