The Structural Adaptations That Mediate Mechanical Load-Induced Changes in Muscle Mass

During the last century, it has become clear that mechanical signals play a pivotal role in the regulation of skeletal muscle mass. For instance, numerous studies have shown that an increase in mechanical loading will lead to an increase in muscle mass, and a decrease in mechanical loading will lead to a decrease in muscle mass. These same studies have not only led to the widely adopted terms of "mechanical load-induced growth" and "disuse atrophy," but they have also shaped our understanding of the macroscopic, microscopic, and ultrastructural adaptations that contribute to the changes in muscle mass. These structural adaptations serve as the foundational events via which mechanical signals regulate skeletal muscle mass and, in this chapter, we will explore what is known about these adaptations and pinpoint the critical gaps in knowledge that remain to be filled.