The addition of nuclei to growing muscle fibers is a strategy used by the fiber to maintain a constant ratio of cell volume per nucleus. The volume of cytoplasm surrounding an individual nucleus is termed the myo- nuclear domain (1). The biological significance of the myonuclear domain is that a single nucleus can sus- tain the necessary gene expression (i.e., production of proteins) only for a limited area of cell volume. There- fore, to maintain a constant myonuclear domain, new nuclei (obtained from satellite cells) are incorporated into skeletal muscle fibers during growth (47, 49, 79). It follows that to maintain a stable myonuclear