The loss of skeletal muscle function with age often precedes and exceeds loss of mass, indicating that protein quality is as important as protein quantity. Although muscle mass, and hence protein mass, has an impact on overall function, it is equally important to have the correct proteins for cellular tasks and for those proteins to be assembled properly and function well. The matching of well-functioning proteins to the demands of the cell is referred to as protein homeostasis, or proteostasis. The dynamic mechanisms through which proteostasis is maintained is a network of complex interrelated cellular activities such as protein biogenesis, folding, transport and degradation that collectively determine proteome structure and function. This talk will address why it is important to consider proteostasis, rather than just protein mass, in studies of muscle aging. Further, the talk will discuss how to use tracer-based and other methods to address skeletal muscle proteostasis during aging and interventions.