As the motto says, “use it or lose it”. It is known that the lack of physical activity leads to an important decrease of motor function. Such deconditioning effects can be observed when the daily-based physical stress is not sufficient to maintain a sufficient solicitation of the neuromuscular system. More commonly, full or partial body immobilization is used to acutely model muscle disuse. An acute injury often leads to a period of immobilization of the injured limb, resulting in drastic impairments of neural and muscular factors. As well, other less common situation known to cause several impairments of the neuromuscular system are for instance prolonged spaceflights which alleviate the body from gravity constraints.
For decades, limiting the several motor impairments that follow limb immobilization has been a major preoccupation for health care systems. The challenge for rehabilitation after an injury lays in the inability to move the involved limb, while it is recommended to start to exercise as soon as possible to prevent severe deconditioning. Several methods were proposed to reduce the force loss induced by prolonged immobilization. For example, neuromuscular electrical stimulation (NMES) that consists of evoking contractions by applying an electrical current over the muscles via surface electrodes, has been shown to provide significant results. While important effects are acknowledged on the nervous system, this method is however mainly dedicated to counteract the muscle impairments (atrophy, decrease of contractile properties, etc.). On the opposite, the use of motor imagery (MI) that consists of asking participants to mentally simulate actions without actually performing them, was also shown to reduce the force loss induced by limb immobilization, but mainly by acting over central component (cerebral network, voluntary activation, etc).
The novelty of the present project lies in the combination of those two methods: muscle stimulation and mental training. Subsequently, this project seeks to propose such a combined approach to maximize the effect of rehabilitation programs from central to peripheral aspects. By gathering two fields of research, i.e. neurosciences and physiology, and associating cutting-edge techniques from those fields such as cerebral imaging and muscle ultrasonography, this project intends to draw a clear picture of the whole neuromuscular system deconditioning. Indeed, while many studies focused on either brain function, by using cerebral imagery, or muscle function, by using intracellular physiology techniques (biopsies), to date no study fully investigated the brain-to-muscle system as a whole. Particularly, the involvement of the nervous networks linking both central and peripheral levels, i.e. the medullar network, remains unknown. Accordingly, this project will aim at deciphering corticospinal and spinal networks plasticity during prolonged limb disuse and its adaptation to combined NMES and MI rehabilitation programs.