Muscle Growth

Skeletal myogenesis begins in the embryo with proliferation and differentiation of muscle progenitor cells that ultimately fuse to form multinucleated myofibers. After mid-gestation, muscle growth occurs through hypertrophy of these myofibers. The most rapid growth phase occurs in early postnatal life, resulting in the expansion of muscle mass from 25% of lean mass at birth to 45-55% at maturity. These two phases of muscle growth are regulated by distinct molecular mechanisms engaged by extracellular cues and the intracellular signaling pathways and regulatory networks they activate.

Nutrients influence muscle growth by both providing the necessary substrates and eliciting extracellular cues which regulate the signal transduction pathways that control the fibers’ anabolic processes. The uniquely large capacity of immature myofibers for hypertrophy is enabled by their ability to expand their myonuclear population through proliferation of muscle precursor cells (satellite cells), and a heightened capacity and sensitivity of protein synthesis to feeding-induced changes in plasma insulin and amino acids. With maturation, satellite cells become quiescent, limiting myonuclear accretion, and the muscles’ capacity for protein anabolism progressively diminishes. The early developmental phases, therefore, represent critical windows for muscle growth which, if disrupted, result in muscle mass deficits that are unlikely to be entirely recoverable.       

The most rapid growth phase occurs in early postnatal life, resulting in the expansion of muscle mass from 25% of lean mass at birth to 45-55% at maturity.  The early developmental phases, therefore, represent critical windows for muscle growth which, if disrupted, result in muscle mass deficits that are unlikely to be entirely recoverable.