Abstract
For decades, scientific researches in the spatial and clinical fields, confront among various issues with that of the musculoskeletal system deconditioning and to its prevention. At the muscular level, more specifically, deconditioning is characterized, in the case of prolonged bed rest for example, or even during a space flight, by a decrease in maximum strength, a loss of muscle mass, and an increase in fatigability. Currently, the various mechanisms initiating the establishment of this deconditioning, as well as their interactions, are still incompletely described, and to date, no method makes it possible to completely prevent the dysfunctions and structural changes observed during a period of inactivity or during ageing. In a first study, conducted under the aegis of the French Space Agency (CNES), and experimenting the drastic model of dry immersion in healthy humans, we were able to show that after only 5 days of hypoactivity, muscle deconditioning is already fully underway, resulting in a muscle fiber atrophy of about 20%, and a decrease in maximum strength of about 15%. The initiation of this deconditioning is associated with a negative protein balance, as well as an alteration of mitochondrial function and REDOX balance. Four other studies were conducted using a model of hypoactivity (hindlimb suspension) in mice and/or in male and female aging mice. Our results have mainly highlighted that ergothioneine supplementation (an antioxidant and anti-inflammatory genes activator), coupled with an aerobic physical activity program, can largely prevent muscle deconditioning during aging. The ergothioneine supplementation seems more specifically responsible for preventing the loss of strength and muscle mass, while the aerobic-type physical activity program seems to be more specifically associated with preventing increased fatigability. These thesis works have contributed, on the one hand, to complete the knowledge related to the early molecular mechanisms of muscle deconditioning, and on the other hand to enrich knowledge on prevention methods. Currently, combinations of countermeasures seem unavoidable, mainly associating physical activity with nutritional supplements, in order to prevent or slow down muscle deconditioning during aging, during space flight, or during clinical bed rest. The field of researches in this field is still currently open to multiple investigations, which will mainly contribute to the optimization of the health management of human faced with adverse environments, chronic hypoactivity periods, or simply in the context of aging better.