Skeletal muscle stem cells (also known as MuSCs or satellite cells) are essential for sustaining muscle homeostasis and repairing muscle injury throughout adulthood. In vivo, MuSCs reside in a tightly regulated cellular niche composed of biochemical and physical cues that preserve the cells in a quiescent, dormant state. In response to injury, inflammatory cells such as macrophages and neutrophils secrete cytokines that alter the niche dynamics, driving MuSCs into an actively proliferating phenotype that generates additional MuSCs and myogenic precursors known as myoblasts, which in turn fuse to become mature myofibers. This regenerative capacity has made MuSCs a promising candidate population for stem-cell based therapies to treat chronic and acute muscle injuries. However, the complex dynamics of the MuSC niche in quiescence and activation are not yet fully understood, severely limiting the efficacy of current therapeutic approaches. Thus, there is a pressing need for detailed characterization of the intracellular signaling pathways MuSCs utilize to respond to niche signals. In this dissertation, I analyze the combinatorial effects on myoblast phenotype of cytokines and growth factors known to activate contrasting phosphoprotein signaling pathways such as p38_/_ MAPK, PI3K/Akt, JNK, and JAK/STAT. I use a partial least-squares regression model to correlate short-term phosphoprotein activation with eventual proliferation and differentiation, identifying how elevated signaling can imply different cell fates based on the timing of the signal relative to the initial stimulation. This model captures the crosstalk between the interrelated signaling pathways and enables prediction of cell fate based on intracellular signaling state. I leverage these findings and concepts in a practical context by establishing a protocol for expanding ex vivo MuSC populations that relies on regulation of signaling pathways in response to multiple extrinsic cues. I demonstrate how the inflammatory cytokines TNF-, IL-1, IL-13, and IFN-_ can be combined with delayed inhibition of p38_/_ to induce 109-fold expansion of functional MuSCs when cultured on soft laminin-coated hydrogels for five weeks. The work in this dissertation represents a significant step toward understanding how intracellular signaling drives MuSC phenotype and establishing a robust autologous MuSC transplantation therapy to treat chronic and acute muscle injuries.