Many previous authors have provided data and interpretation critical to understanding the basicmechanisms responsible for muscle atrophy at old age. Figure 2.2 shows a proposed model of mechanismsassociated with accelerated sarcopenia. These mechanisms range from systemic changessuch as reduced production of anabolic hormones to cellular mechanisms governing myofiber sizeand viability. These data, together with the discovery of yet unknown pathways, are critical to thecreation of new therapeutic approaches. However, we argue that these approaches should be developedwithin the context of the paradigm proposed here.