Muscle Building: A Complete Guide Hypertrophy, also known as muscle building, is a complicated physiological process in which resistance training causes muscle fibers to grow. Fundamentally, muscle growth happens whslots megawaysen the body is exposed to a stimulus that damages muscle fibers in tiny ways. The body begins a process of repair in response to this damage, creating new proteins to rebuild the muscle and make it bigger and stronger than before. A person's ability to build muscle is influenced by a number of factors, including age, hormone levels, and genetics. The concepts of progressive overload must be understood in order to build muscle.