 Muscles are composed of cells and proteins which are constantly being broken down and rebuilt. When there is too much breakdown or not enough rebuilding, muscle atrophy occurs. This process is caused by various factors, including disease, age, and lack of exercise. Mechanisms involved in muscle atrophy include proteolysis, breakdown of proteins, autophagy, self-eating, and apoptosis, cell death. These processes are regulated by signalling pathways that are influenced by mechanical stress, physical activity, and nutrition. Understanding how these pathways work could lead to new treatments for muscle atrophy in metabolic and neuromuscular diseases. This article was authored by Paolo Bonaldo and Marcos Andrii.