Exercise and the control of muscle mass in human.

During the course of life, muscle mass undergoes many changes in terms of quantity and quality. Skeletal muscle is a dynamic tissue able to hypertrophy or atrophy according to growth, ageing, physical activity, nutrition and health state. The purpose of the present review is to present the mechanisms by which exercise can induce changes in human skeletal muscle mass by modulating protein balance and regulating the fate of satellite cells. Exercise is known to exert transcriptional, translational and post-translational regulations as well as to induce epigenetic modifications and to control messenger RNA stability, which all contribute to the regulation of protein synthesis. Exercise also regulates the autophagy-lysosomal and the ubiquitin-proteasome pathways, the two main proteolytic systems in skeletal muscle, indicating that exercise participates to the regulation of the quality control mechanisms of cellular components and, therefore, to muscle health. Finally, activation, proliferation and differentiation of satellite cells can be enhanced by exercise to induce muscle remodelling and hypertrophy. Each of these mechanisms can potentially impact skeletal muscle mass, depending on the intensity, duration and frequency with which the signal appears.